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Ecological characterization of tree species for guiding forest management decisions in seasonally dry forests in Lomerı́o, Bolivia
Forest Ecology and Management 113 (1999) 201±213
Ecological characterization of tree species for guiding forest management decisions in seasonally dry forests in LomerõÂo, Bolivia M.A. Pinarda,c,*, F.E. Putzb, D. RumõÂzc, R. GuzmaÂnc, A. Jardimd b
a Department of Forestry, University of Aberdeen, Aberdeen AB24 5UA, UK Center for International Forestry Research (CIFOR), P.O. Box 6596, JKPWB, Jakarta 10065, Indonesia c Proyecto BOLFOR, Casilla #6204, Santa Cruz, Bolivia d Museo Noel Kempf Mercado, Casilla #2489, Santa Cruz, Bolivia
Received 13 October 1997; accepted 1 July 1998
Abstract When the goal of natural forest management is to maintain the biodiversity and ecological integrity of the forest while harvesting timber, the silvicultural systems employed must promote timber production and reduce negative impacts on nontimber resources. To foster development of such a system in a seasonally dry tropical forest in LomerõÂo, Bolivia, we classi®ed tree species according to their relative timber value, importance as food for vertebrate frugivores, and vulnerability to population declines when subjected to logging. We used this classi®cation to identify a management system appropriate for the commercial species and to evaluate the compatibility of the system with the regeneration requirements of tree species that produce important food for mammalian wildlife. About half of the tree species in the site are commercially valuable for their timber and a similar proportion are considered of value as food for wildlife. A tree species rating for vulnerability to disturbance appeared to be independent of both timber and wildlife values. A silvicultural system that includes even-aged groups of trees within an uneven-aged matrix appears more suitable to the multiple goals of management in this forest than either an even-aged or uneven-aged (single tree selection) management system. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Biodiversity; Bolivia; Harvesting systems; Logging; Natural forest management; Semi-deciduous tropical forest; Silviculture
1. Introduction Understanding the ecology of tree species is central to sustainable forest management and conservation. Most fundamentally, a species' regeneration requirements dictate, in part, which silvicultural systems are appropriate for its management (e.g. Smith, 1986). A *Corresponding author. Tel.: +44-1224-274110; fax: 44-1224272685; e-mail: [email protected]
species' ability to resprout after breakage, for example, may re¯ect its vulnerability to population declines in areas with selective logging (Martini et al., 1994). From a wildlife perspective, species that produce ¯eshy fruits during periods of general fruit scarcity may be of special importance due to their value as food for frugivorous mammals and birds (Foster, 1982; Terborgh, 1986). In this paper we consider the ecological characteristics of tree species in semi-deciduous forests of the
0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0378-1127(98)00426-5
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LomerõÂo region of Bolivia with the goal of identifying harvesting systems that enhance the regeneration of these species. In a mixed species forest, a single harvesting system will favor some species over others. If the goal of management is to maintain biodiversity and ecological integrity of the forest while harvesting timber, decisions need to be made about how to balance timber production against the associated negative impacts on the residual forest. To identify tree species likely to experience population declines as a consequence of timber harvesting, we use a set of characteristics to rate species on their vulnerability to disturbances. We test for correlations among ecological characteristics, timber values, and wildlife values to identify groups of species (or `guilds') within the forest community. Finally, we discuss the apparent compatibility of the recommended silvicultural system and maintenance of biodiversity in this forest. 1.1. Silvicultural issues Silvicultural systems generally involve the harvest of some trees followed by treatments to enhance regeneration, increase growth rates, or improve the quality of commercial trees within the residual forest. The harvesting (or tree selection) method used should be appropriate to the timber species' regeneration requirements, and whether or not the forest is to be maintained in even-aged or uneven-aged stands. A variety of harvesting systems is used in natural forest management (Table 1). The systems vary in the
degree of disturbance to the residual forest and differ in terms of the post-harvest habitats created for regeneration. For example, single tree selection methods result in relatively small felling gaps that foster development of shade-tolerant species and species represented by advanced regeneration (e.g. Gottfried, 1983; Stokes et al., 1993). Group tree selection methods result in larger felling gaps; within the center of these gaps, conditions may be appropriate for regeneration of shade-intolerant species (Hartshorn, 1989; Murphy et al., 1993; Meadows and Stanturf, 1997). Group selection results in aggregations of even-aged trees within an uneven-aged stand. In this study we recommend species for either evenaged or uneven-aged management based on their apparent requirements for, or tolerance of, shade during seedling establishment and development. We also discuss the suitability of particular felling systems (e.g. single tree selection, shelterwood; Table 1) for the commercial species as a group, considering timber values, potential for and environmental requirements of natural regeneration, abundance and distribution of mature trees, and the other goals of forest management. 1.2. Vulnerability to disturbance associated with timber harvesting Damage to residual trees, soil, and other non-timber resources during timber harvesting is variable and depends on environmental conditions during harvest,
Table 1 An outline of two basic timber management systems with examples of felling methods used for each system (Wenger, 1984; Matthews, 1989) Felling method Uneven-aged system Even-aged systems
Single tree selection Uniform clearcut Shelterwood Group tree selection Strip cuts
Features Remove some trees at relatively short intervals, maintaining an uneven-aged stand (i.e. one that contains a mixture of at least three distinct age classes within the forest). Mature trees, generally as scattered individuals, are removed during each harvest. Remove all or most trees during harvest and rely on new regeneration for producing the next even-aged stand. All trees on a site are removed in a single felling, relying on regeneration from artificial seeding, seed banks, seed rain from neighboring stands, or from planting; new crop is even-aged. Trees are removed in a series of cuts, the new stand is regenerated naturally or artificially under the old stand before all of the old stand is removed; new crop is even- or unevenaged. Groups of adjacent mature trees are removed during each harvest; new crop is regenerated naturally or artificially in the scattered gaps, and is even-aged. Trees are removed in strips; new crop within a strip is even-aged.
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
harvest intensity, felling methods used, and the care with which harvesting is carried out (e.g. Ewel and Conde, 1980). The selective extraction of timber from a forest, even where low impact techniques are used, causes damage to the residual stand. In areas where logging causes extensive structural damage and creates large felling gaps, tree species that regenerate in high light and are fast-growing, are likely to be favored by logging (Fox, 1976; Gottfried, 1983; Chandrashekara and Ramakrishnan, 1994) although competition with invading vines and other weeds may impede establishment (e.g. Putz, 1991). Alternately, populations of species that regenerate in shade may be vulnerable to severe logging disturbance. Certain ecological characteristics may be indicative of a species' vulnerability to population declines in timber harvesting areas. For example, in an analysis of Amazonian tree species, Martini et al. (1994) used the following characteristics to describe vulnerability: (1) long-distance seed dispersal ability; (2) sapling abundance; (3) ability to grow rapidly; (4) ability to resprout after cutting or breakage; (5) capacity to withstand ®re; (6) broadness of geographic range; and, (7) adult abundance. Other characteristics that may be useful include species regeneration strategies (e.g. seed longevity in soil), resistance to pathogens following damage, and susceptibility to lianas or herbivores. Given the large variability in forest composition and ecology found among tropical forests, the appropriate suite of characteristics useful for describing a tree species' vulnerability to disturbance will vary regionally. Based on our experience in this forest, we use bark thickness, susceptibility to lianas, capacity for seed dispersal, and shade tolerance of seedlings and saplings to predict relative vulnerability to disturbance. 1.3. Management objectives Many forest managers are striving to identify ways to manage forests for timber while protecting the biological and physical resources of the forests; these resources include biodiversity, water quality, soil conservation, and ecological functions (e.g. Burton et al., 1992; Maser, 1994). This goal of managing for timber while maintaining biodiversity presents potentially con¯icting objectives. Development of suitable management plans will require decisions regarding trade-
203
offs between activities that maximize timber production and those that reduce negative impacts on the biological integrity of the system. In this paper we consider the silvicultural needs of commercial tree species and the compatibility of felling systems with the regeneration requirements of non-timber tree species and maintenance of tree species diversity in a tropical dry forest in Bolivia. 2. Methods 2.1. Study site The semideciduous forests of LomerõÂo are in the Ä u¯o de Chavez, Santa Cruz, Bolivia Province of N 0 (16845 S, 618450 W) at an elevation of 400±600 m. Mean annual rainfall is 1130 mm and mean temperature 248C (ConcepcioÂn Meteorological Station, cited in Killeen et al., 1990). The region is characterized by its undulating topography and the vegetation, a mosaic of natural savanna and dry-to-subhumid forest. Soils are described as well-drained Inceptisols, Al®sols (Killeen et al., 1990), and Oxisols (Ippore, 1996). Mean forest canopy heights are 12±18 m with emergent trees to 30 m. Total basal area for trees >10 cm dbh averages about 23 m2 haÿ1. About 140 tree species have been recorded with 19±27 species found per hectare (Killeen et al., 1990). About 60% of total basal area (trees >10 cm dbh) is composed of legumes. Much of the forest of LomerõÂo is within the community lands of an indigenous group, the Chiquitanos. The objective of the current management plan for the forests of LomerõÂo is to sustainably produce timber while minimizing negative impacts on the other biological and physical resources in the forest. The Chiquitanos rely heavily on wild meat to supplement their protein intake; consequently, a silvicultural system that maintains critical habitats for large mammals is of particular interest. Three of the 15 timber tree species currently being harvested are considered high value, relative to other marketable timbers in the country, and are saleable on international markets. The remaining 12 species had relatively low value in Bolivia at the time of the study (1996), though some of these species are considered of high value in other Latin American countries. Forestry operations of Chiquitano communities were certi®ed as sustainable by
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SmartWood in 1995, thus the possibility of entering green markets exists and may increase sale values and market access for some of the lesser known species. Timber harvest activities are restricted to the dry season (May±October) and are implemented in 400 ha blocks. Log extraction routes are opened by hand and a farm tractor is used for skidding logs to a loading area. Logging intensity ranges from 2 to 5 trees haÿ1 (3±10 m3 haÿ1). Damage to the residual stand is principally in the form of small felling gaps, skid trails, and roads. Roads and skid trails cover only 2±4% of the site and felling gaps are generally only 40±70 m2 (Camacho, 1996). The logs are sawn in a communityowned mill and the lumber is then transported by truck 8±10 h to Santa Cruz for sale. The natural disturbance regime for this forest is likely to include infrequent disturbance related to droughts and ®re or slash and burn agriculture. Low-intensity ground ®res occur frequently in the savannas bordering the forests of LomerõÂo but it is unclear how frequently ®res penetrate the forests. The predominance of relatively thin-barked canopy species suggests that the forest characteristic of the region, at present, did not develop with frequent ®res (Pinard and Huffman, 1997). Recorded human occupancy of the region dates only to the 1700s (Killeen et al., 1990); however, it is likely that humans have occupied the region much earlier (Meggers, 1987). Logging may increase the forest's vulnerability to ®re through changes in microclimate and fuel loads (Uhl et al., 1988; Uhl and Kauffman, 1990; Holdsworth and Uhl, 1997). As part of a larger, integrated forest management project, 100 permanent plots (2050 m2) were established following a strati®ed random design in a 400 ha block of forest in 1994 for describing forest structure and composition prior to logging (Mamani, 1996; Killeen et al., in review). All tree species that obtain a dbh of 15 cm were included in the analysis. Small stature species (maximum tree sizes of <30 cm dbh) may not be commercially viable for timber but, because they represent a signi®cant proportion of the diversity (25 of 69 arboreal species) in the forest, we included them in the study (hereafter, subcanopy species). Within each plot, trees >=20 cm dbh were identi®ed to species and dbh and grade of infestation of lianas was recorded (1no lianas present; 2one to few lianas on stem; 3few lianas in crown; 4lianas
covering crown). Nested subplots (2025 m2 and 1010 m2) were established within each plot and the number of saplings (10±20 cm dbh, and 5± 10 cm dbh) by species were recorded, respectively. Commercial status and timber values were based on the timber markets in Santa Cruz, Bolivia (A. Guillen, pers. comm.). Species were classi®ed by the importance of their fruits for local mammal and bird species, based on interviews with local hunters and stomach contents of game taken by these hunters (Guinart, 1997; R. Aguape, unpubl. data). 2.2. Selection of characters ± Silvicultural considerations Of the range of possible characteristics for describing the ecology of tree species in the study area, we selected those that represent the union of characteristics that we considered useful and those for which we had reliable data (Table 2). A general classi®cation by shade tolerance was used to match silvicultural systems with regeneration requirements of the species. We classi®ed tree species on the basis of their regeneration requirements (hereafter, shade tolerance class) for light or tolerance of shade based on ®eld observations, some as yet unpublished physiological studies, interviews with local foresters, and references to the literature (Pinard et al., 1996). We used three tolerance classes and assigned each a score as follows: (1) species that have relatively light demanding regeneration requirements and establish on forest edges or in large gaps (>200 m2); (2) species that can establish in canopy gaps of various sizes but also in the forest understory; and, (3) species with seed that germinates in the shade and seedlings that are shade-tolerant. Five of the 61 species could not be matched to a shade tolerance class because of lack of information. 2.3. Selection of characters ± Vulnerability to disturbance To classify the species in terms of their vulnerability to disturbance, we used the following characteristics: bark thickness; seed dispersal capacity; shade tolerance; and resistance to lianas (Table 2). Although many other characteristics are potentially important and useful, we limited ourselves to characteristics for which we had data. Adult tree abundance was not
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Table 2 Ecological characteristics used to determine species' vulnerability to population declines in areas with disturbance associated with timber harvesting Characteristics
Score1
Score2
Score3
Shade tolerance of regeneration Susceptibility to fireb Inverse of capacity for propagule disperalc Susceptibility to invasion by lianasd Adult tree raritya Sapling rarity (5±10 cm dbh)e
High light only, large gaps Resistant (>18 mm) High capacity Low (20%) Common (>5 haÿ1) Common (20 haÿ1)
Partial shade, small gaps Intermediate (10±18 mm) Intermediate capacity Medium (between 20 and 45%) Intermediate (1±5 haÿ1) Intermediate (5±20 haÿ1)
Partial or full shade, understory Sensitive (<10 mm) Low capacity High (45%) Rare (<1 haÿ1) Rare (<5 haÿ1)
Adult treea and sapling rarity characteristics were not included in the calculation of vulnerability; they are included here and assigned a score to allow for an analysis of correlations between characteristics. a Trees >20 cm dbh, unless noted as subcanopy trees considered adults when >10 cm dbh. b Based on bark thickness for canopy trees 20 cm dbh, subcanopy trees 10±15 cm dbh. c Based on propagule size, presence/absence of wings, and whether or not it is animal-dispersed (see text). d Percentage of adult trees with lianas on stem and in crown (grades 3 and 4). e For palms, plants were considered saplings if they were stemless but had leaves >2 m long.
included because species may be rare due to lack of disturbance. Bark thickness was included as an indication of a species' ®re tolerance (Hare, 1965; Ryan and Reinhardt, 1988; Pinard and Huffman, 1997). We measured bark thickness (at 0.5±1.3 m) on trees 15± 25 cm dbh; N3±10 individuals per species. Thirteen species lacked bark thickness data. Bark thickness classes are based on studies of bark thermal properties of 16 local species that indicate 18 mm thickness as the threshold or minimum thickness for a tree to withstand low intensity ground ®res (Pinard and Huffman, 1997). Our classi®cation of seed dispersal capacity is based on propagule size and the presence or absence of structures to assist dispersal (e.g. hairs, wings, ¯esh). Although seed size is related to dispersal mode (Hammond and Brown, 1995), the negative correlation between dispersal distance and propagule size is not strong; many species have relatively large propagules but also possess structures that increase the likely distance of dispersal. Based on herbarium material and discussions with local botanists, we scored the species' propagules, by volume (1 for small, <50 mm3; 2 for medium, 50±1000 mm3; 3 for large, >1000 mm3), and then subtracted 1 from the score if the propagule possessed a wing, hairs or pappus, a ¯eshy exocarp, or an aril. Thus, the lower the score, the better the predicted dispersal capacity. Susceptibility to lianas was estimated as the proportion of adult trees in the study area that had lianas in their crowns. Susceptibility was considered low
when less than 20% of trees had lianas in their crowns (score1), and high when greater than 45% of trees had lianas in their crowns (score3). The intermediate condition was scored 2 (Table 2). We further scored species by the rarity of adult trees and saplings (5±10 cm dbh) into three groups: common; intermediate; or, rare (Table 2). Although the minimum diameter for fruit production varies with species and environmental conditions, we considered trees above a threshold diameter to be capable of producing fruits. For species that reach dbh >=40 cm, individuals >=20 cm dbh were considered adults; for species that reach maximum dbh of less than 30 cm dbh, individuals >=10 cm were considered adults. 2.4. Data analysis A vulnerability score was calculated for each species based on the mean of the four contributing characters (shade tolerance, resistance to lianas, seed size, bark thickness). We used a mean rather than a sum because for some species (N13), we were unable to assign a species score for all characteristics. Larger scores re¯ect a higher vulnerability to disturbance. ANOVA followed by pairwise comparisons (Least Squares Difference, Saville, 1990) were used to compare vulnerability scores for timber and wildlife value classes. To identify correlations among the ecological characteristics, we conducted a correlation analysis using Goodman±Kruskal -coef®cients for
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ordinal data (Goodman and Kruskal, 1954 cited in Wilkinson et al., 1992). 3. Results 3.1. General classification Only 108 of the 140 tree species found in the semideciduous forests of LomerõÂo, were recorded in our 400 ha study site. Of these, 69 species obtained diameters of at least 15 cm and were classi®ed on the basis of their ecological characteristics (Table 3). Based on market conditions at the time of the analysis, 31 of the 69 species were considered of commercial value for their timber (Table 4). Of the commercial species, 11, representing 15% of total basal area, had a relatively high value and 20 species, or 65% of total basal area, had a relatively low value. The 38 species that were considered to have no commercial timber value represented only about 20% of the total basal area (trees >10 cm dbh). Twenty species were considered of high value for vertebrate frugivores; these species represented 9% of the basal area (Table 4). Generally, the more abundant tree species were considered of low value to frugivores. The 15 tree species of intermediate value to frugivores represented about 16% of the basal area. 3.2. Silvicultural systems Species were matched to a general silvicultural system (even- or uneven-aged management) based on their regeneration requirements. For species with shade-tolerant regeneration requirements (scores 2 and 3), we suggest uneven-aged management with a single-tree selection harvest system. For species with shade-intolerant regeneration (score 1), we suggest even-aged management. Rather than assign each species to a particular felling system within even- or uneven-aged management, we discuss the suitability of major felling systems for the group of commercial species. Based on seedling shade tolerance, half of the commercial timber species at the site appear compatible with even-aged management, and half compatible with uneven-aged management. In terms of total basal area, 37 and 43%, respectively, were commercial
and compatible with even- and uneven-aged management (Table 5). When all species were considered, 36% appeared compatible with even-aged management and 59% compatible with uneven-aged management (score 3 could not be classi®ed). For the species considered of high value to wildlife, the classi®cation was 19 and 81% for even- and uneven-aged management, respectively (Table 5). 3.3. Vulnerability On a scale of 1±3 representing increasing vulnerability to disturbance, scores ranged from 1.00 to 2.75 (median2.00, N69; Table 6). The scores had a bimodal distribution suggesting two distinct groups of species, the ®rst with relatively low vulnerability and a mean score of 1.65 (N38), the second, with relatively high vulnerability and a mean score of 2.51 (N30; Fig. 1). Using the division of species into two groups based on vulnerability scores, the number of species classi®ed with low and high vulnerability was independent of both the species importance for wildlife (X20.84, d.f.2, p0.66) and value for timber (X20.98, d.f.2, p0.61). 3.4. Correlations among variables The four characteristics used for assessing vulnerability to disturbance are not strongly correlated with one another. The strongest association observed was between shade tolerance and susceptibility to ®re (Table 7); thin-barked species tended to have shadetolerant regeneration. Shade tolerance was weakly negatively correlated with capacity for dispersal (i.e. greater shade tolerance was associated with poorer dispersal). Tree and sapling rarity were positively correlated. Sapling rarity was negatively correlated with shade tolerance, indicating that the least abundant sapling species were relatively light demanding. Adult tree rarity, however, was not correlated with shade tolerance; species with shade-tolerant and species with shade-intolerant regeneration strategies were equally represented among the more common overstory species (Table 7). Timber values were negatively correlated with wildlife values, and weakly negatively correlated with shade tolerance.
Low Low Inter Low Inter Low Low Low Inter Low Low High Low Low Low Low High Inter Low Low High High Low Inter Low Inter High Low Low High High Low Inter Low Inter Inter
Family
Mimosaceae Caesalpinioideae Caesaplinioideae Apocynaceae Bombaceae Mimosaceae Bignonaceae Fabaceae Bombaceae Fabaceae Anacardiaceae Caesalpinioideae Apocynaceae Ulmaceae Phytolaccaceae Anacardiaceae Palmae Lecythidaceae Fabaceae Combretaceae Flacourticeae Capparadaceae Rubiaceae Nyctaginaceae Nyctaginaceae Fabaceae Anacardiaceae Meliaceae Polygonaceae Moraceae Moraceae Papilionoideae Bombacaceae Papilionoideae Nyctaginaceae Bombaceae
Tree species
Anadenanthera colubrina (Vell.) Brenan Poeppigia procera C. Presl Caesalpinea floribunda Tul. Aspidosperma rigidum Rusby Chorisia speciosa St. Hilaire Acacia polyphylla DC. Tabebuia impetiginosa (Mart. ex DC) Standl. Centrolobium microchaete Lima ex G. P. Lewis Eriotheca roseorum (Cuatr.) Meyer Machaerium scleroxylon Tul. Astronium urundeuva (Fr. Allemao) Engler Peltogyne heterophylla M. de Silva Aspidosperma cylindrocarpon Muell. Arg. Phyllostylon rhamnoides (Poisson) Taub. Gallesia integrifolia (Sprenge) Hams Schinopsis brasilensis Engl. Scheelea princeps (C. Martius) G Karsten Cariniana estrellensies (Raddi) Kuntze Machaerium acutifolium Vogel Combretum leprosum Mart. Casearia gossipiosperma Briq. Capparis prisca J F Macbr. Simira rubescens(Benth.) Steyerm. Neea anisophylla Ernst Bougainvillea modesta Hiermerl Platypodium elegans Vog. Spondias mombin L. Cedrela fissilis Vell. Ruprechtia laxifolia Meisner Sorocea sprucei (Baippon) Macbr. ssp. saxicola Hassler C.C. Berg. Ficus gomelleira Kunth and Boucher Cyclobium blanchetianum Tul. Ceiba samauma (Mart.) Schum. Amburana cearensis (Allemao) A.C. Smith Neea hermaphrodita S. Moore Uel Pseudobombax marginatum (St. Hilaire) Rubyns Low None None High None None
None High Low High Low Low None Low None Low Low None Low None None None Low None None High None None
Low Low Low Low None Low High High
Even Even Uneven Even
Even
Even Uneven Even Uneven Uneven Uneven Uneven Even Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Even Even Uneven
Even Uneven Uneven Uneven Even Uneven Even Even
3 3 2 3 1 3
2 1 2 2 2 2 2 2 2 2 1 2 1 1 1 1 2 2 2 3 2 3
1 1 1 1 1 1 1 1
3 3 3 3 1 3
3 2 3 3 3 2 2 3 3 2 2 2 1 2 1 2 3 3 3 3 3 3
2 1 2 2 2 2 3 3
1 1 3 1
1
1 3 1 3 2 3 3 1 2 3 3 2 3 3 3 3 2 3 2 1 1 3
1 3 2 2 1 2 1 1
1 1 1 1 2 1
1 2 1 1 2 2 1 1 1 1 2 1 1 1 1 2 1 2 2 1 2 1
2 2 2 2 1 1 1 2
2 3 3 1
3
1 3 2 3 1 3 3 1 1 1 2 3 3 3 3 3 3 2 1 1
2 3 2 1 1 3 2 3
3 2 3 2 3 3
3 3 2 3 3 3 3 2 1 2 3 3 3 3 3 3 3 3 1 3 1 1
2 3 3 2 3 3 3 3
2.00 1.50 1.75 1.75 2.75 1.50
1.50 2.75 1.50 2.50 2.00 2.75 2.50 1.25 1.25 1.75 2.50 2.25 2.50 2.50 2.50 2.75 2.25 2.50 1.50 1.50 1.33 1.67
1.75 2.75 2.25 1.75 1.50 2.25 1.75 2.25
0.115 0.115 0.112 0.096 0.096 0.059
0.735 0.714 0.690 0.663 0.558 0.499 0.467 0.435 0.392 0.320 0.307 0.230 0.196 0.186 0.159 0.154 0.150 0.129 0.129 0.125 0.123 0.119
5.199 3.380 1.045 0.961 0.946 0.929 0.861 0.763
Inverse of Susceptibility Susceptibility Vulnerability Basal Wildlife Timber Management Adult Sapling Shade to fire to Lianas score area value value system rarity rarity tolerance of capacity regeneration for dispersal
Table 3 Characteristics of tree species of the semideciduous forests of LomerõÂo
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213 207
Low High Low High High Low Low Inter Low High Low Inter High High High High Low High Inter Low Inter Low
Papilionoideae Mimosoideae Papilonoideae Sapotaceae Urticaceae Tiliaceae Combretaceae Bignoniaceae Vochysiaceae Hippocrataceae Rubiaceae Bignoniaceae Nyctaginaceae Moraceae Mimisoideae Humiriaceae Fabaceae Annonaceae Moraceae Tiliaceae Opiliaceae Fabaceae
Low Low None None None None Low None None None None High None None None None Low None None None None High
None Low None None High None High Low None None
Even
Uneven Uneven Uneven Even Uneven Even Even Uneven Uneven Uneven Even Uneven Even Uneven Uneven Uneven Uneven Uneven Even
Uneven Uneven Uneven Uneven Even Uneven Even Even Uneven Even 2 3 3 3 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
3 3 3 3 3 2 2 3 3 3 3 3 3 3 2 2 3 3 3 3 3 3 3 3 3 3 3 2 3 3 3 3
3 2 3 2 2 3 3 3 3 3
1
3 2 3 1 2 1 1 3 3 3 1 3 1 3 3 3 3 3 1
3 2 3 3 1 3 1 1 3 1
1 1 1 1 1 1 1 2 1 2 1 1 2 2 1 1 1 1 2
1 2
1 2 1 1 2 2 1 2 2 2
1
3
3
2 3 2 3 3
3 3 3 2 1
3
3
1 1 2 3 1 3
3 3 1 3 3 3 1 3 3 3 1 3 1 3 3 3 1 1 3
2 2
1 3 3 3 1 3 3 3 3 3 1.50 2.50 2.00 2.50 2.00 1.75 1.75 1.50 2.33 1.75 2.75 1.75 2.75 1.50 2.33 2.00 2.75 2.33 2.33 1.50 1.00 1.75
1.50 2.00 2.25 2.50 1.25 2.75 1.67 2.00 2.75 2.00
0.026 0.026 0.023 0.022 0.020 0.019 0.016 0.016 0.015 0.013 0.011 0.011 0.010 0.009 0.007 0.006 0.006 0.005 0.005 0.004 0.004 0.004
0.057 0.053 0.050 0.049 0.041 0.041 0.039 0.038 0.031 0.029
Species are listed by basal area (trees 10 cm dbh). See text and Table 2 for definitions of the scores (0±3) for the characteristics. The management system is based on shade tolerance of regeneration, even-aged management is recommended for score 1, uneven-aged management is recommended for scores 2 and 3. When no shade tolerance score was assigned, no management system was assigned. Vulnerability score per species was calculated as the mean of scores for shade tolerance, susceptibility to lianas, capacity for propagule dispersal, and bark thickness.
High Low High High Low High Inter High Inter Low
Palmae Apocynanceae Verbenaceae Meliaceae Boraginaceae Annonaceae Lauraceae Caesalpinioideae Nyctaginaceae Polygonaceae
Syagrus sancona Karsten Aspidosperma pyrifolium Mart. Vitex cymosa Bert. Trichilia elegans A. Juss. Cordia alliodora (r. & P.) Cham. Annona cf. jahnii Saff. Ocotea cf. cernua (Nees) Mez Hymenaea courbaril L. Neea cf. ovalifolia Spruce ex J A Schmidt Ruprechtia salicifolia (Cha. et Schlecht.) Meyer Lonchocarpus guillemineanus (Tul.) Malme Inga marginata Willd. Andira inermis (Wright) DC Pouteria gardneriana (A.DC.) Rudlk. Urera baccifera (L.) Gaudich Luehea candicans Mart. Terminalia oblonga (Ruiz and Pavon) Steud. Zeyheria tuberculosa (Vell.) Bur. Callistene sp. Salacia elliptica (Mart.) G. Don Pogonopus tubulosus DC Schumann Tabebuia serratifolia (Vahl.) Nichols Pisonia sapallo Griseb. Cecropia concolor Willd. Samanea saman (Jacq.) Merr. Sacoglottis mattogrosensis Malme Machaerium jacarandifolium Rusby Duguettia guitarensis Benth. Maclura tinctoria (L.) Steud. Heliocarpus americanus L. Agonandra brasilensis Miers Platymiscium ulei Harms
Inverse of Susceptibility Susceptibility Vulnerability Basal Wildlife Timber Management Adult Sapling Shade to fire to Lianas score area value value system rarity rarity tolerance of capacity regeneration for dispersal
Family
Tree species
Table 3 (continued )
208 M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213 Table 4 Summary data for 69 tree species in LomerõÂo Characteristic
Category
Species
Basal area
Wildlife value
1 2 3 1 2 3
33 15 21 38 20 11
17.07 3.70 2.16 4.60 14.95 3.38
Timber value
± ± ± ± ± ±
low intermediate high none low high
(48%) (22%) (30%) (55%) (29%) (16%)
(74%) (16%) (9%) (20%) (65%) (15%)
For each category of wildlife and timber values, total number of species and basal area (percentages noted in parenthesis) per category.
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Table 6 Vulnerability scores for tree species by category of wildlife and timber value Characteristic
Category
Wildlife value
1 2 3 1 2 3
Timber value
± ± ± ± ± ±
Vulnerability score
low intermediate high none low high
2.00 1.95 2.12 2.04 2.09 1.88
(0.48, (0.56, (0.45, (0.52, (0.45, (0.44,
33) 15) 21) 38) 20) 11)
Mean (SD, N) scores are presented for each category.
Table 5 Classification of tree species by recommended timber management system (even-aged or uneven-aged) and by category of wildlife and timber value Characteristic
Wildlife value Timber value
Category
1 2 3 1 2 3
± ± ± ± ± ±
low intermediate high none low high
Basal area (m2 haÿ1)
Species Even
Uneven
Even
Uneven
14 7 4 10 6 9
17 7 17 26 13 2
8.5 1.9 0.2 2.0 6.5 2.0
8.5 1.8 2.0 2.4 8.4 1.4
Total number of species and total basal area are presented for each combination of categories.
Fig. 1. Frequency histogram with vulnerability scores for 69 tree species in LomerõÂo. Higher scores represent an increased likelihood of population declines due to disturbances during timber harvest.
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Table 7 Goodman±Kruskal -correlation coefficients between pairs of tree species characteristics (N55)
Shade tolerance Susceptibility to Lianas Capacity for dispersal Susceptibility to fire Adult tree rarity Sapling rarity Wildlife value Timber value
Shade tolerance
Susceptibility to Lianas
Capacity for dispersal
Susceptibility to fire
Adult tree rarity
Sapling rarity
Wildlife value
0.27 0.45 0.57 ÿ0.21 ÿ0.49 0.39 ÿ0.43
0.25 0.40 ÿ0.28 ÿ0.26 ÿ0.11 0.11
0.01 ÿ0.23 ÿ0.25 ÿ0.38 0.36
ÿ0.19 ÿ0.37 0.13 ÿ0.22
0.83 0.26 ÿ0.09
0.29 0.06
ÿ0.66
Scores assigned to characteristics are defined in Table 2.
4. Discussion The two goals for this study were: (1) to identify a timber stand management system appropriate for the commercial species in our study site in Bolivia; and, (2) to evaluate the compatibility of the recommended system with the regeneration requirements of tree species that produce fruit of particular importance to wildlife. Based on the results of the ecological characterization of commercial species, we recommend a silvicultural approach that combines even- and uneven-aged management. By incorporating single tree and group selection in a spatial mosaic, conditions appropriate for the regeneration of both shade-intolerant and shade-tolerant species could be maintained within the management unit. A mixed system appears more compatible with maintenance of wildlife food species than does the uniform application of either even- or uneven-aged management. 4.1. Silvicultural system Although the high value timber species (N11) in LomerõÂo appear to have ecologies compatible with even-aged management, the commercial species considered as a group (N31) include a broad range of seedling shade tolerance. From the timber producer's perspective, it seems more appropriate to focus on the entire group of commercial species than just on a few high value species because high value species alone currently represent only a small proportion of the available mature timber. Management for the entire group of commercial species requires a silvicultural approach that provides
conditions appropriate for species with shade-tolerant seedlings as well as for species that regenerate only in large clearings. This approach could be developed by mixing two regeneration systems spatially. A spatial mixture might be achieved by felling groups of trees to create scattered gaps, strips, or patches, and by felling single trees in the remainder of the forest matrix (i.e. patch selection method, Leak and Fillip, 1977; Nyland, 1996). This type of mixture has been successfully used for managing bottomland hardwood forests in the southeastern US (Meadows and Stanturf, 1997). The size of the openings made from group felling would need to be matched to the regeneration requirements of the shade-intolerant species (e.g. Marquis, 1965). Narrow strips and gaps >=0.5 ha may provide environmental conditions appropriate for very shadeintolerant species only in the center of the openings. A patch selection approach may be a reasonable simulation of the natural stand dynamics in the forest. While both shade-tolerant and light-demanding species are intimately mixed in the stands, some of the light-demanding species (e.g. Cedrela; Astronium) have clumped distributions that may coincide with old agricultural clearings or hot spots in past ®res. In the seasonally dry forest of LomerõÂo, fruitfall tends to be during the dry season (Bolfor, unpubl. data) and the seeds of many tree species tend to remain in the seed bank only until the rain season commences (Pinard, unpublished data). To achieve suf®cient seedling establishment in large openings, it is likely that natural regeneration would need to be assisted by broadcast seeding or other enrichment treatments. As long as damage to advanced regeneration is controlled in areas kept in uneven-aged stands, probably
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
natural regeneration would be suf®cient to maintain recruitment. An alternative to a patch selection system would be an irregular shelterwood system (Troup, 1952). Irregular shelterwoods are used in Germany and Switzerland to favor both shade-intolerant and shade-tolerant species in the same stand (Matthews, 1989). This approach involves a succession of regeneration fellings with long, inde®nite regeneration periods; the application in Europe generally targets two-to-®ve species. The application of an irregular shelterwood system in the Chiquitano forest where 31 species have commercial timber value may not be practical or ®nancially viable given the need for frequent and scattered stand intervention, the lack of information about species growth rates, and the relatively heavy thinning that would be required to regenerate the more light-demanding species. 4.2. Compatibility of the silvicultural system with maintenance of wildife food production When compared to either a uniform application of even- or uneven-aged management (single tree selection), a mixed system is probably the most compatible with the multiple goals of forest management in LomerõÂo. Application of a uniform even-aged management system would be aimed at creating a forest dominated by light-demanding species with high timber value. In this site, species with high timber value tend to be of low value to wildlife. If the management system were effectively implemented, the majority of the wildlife food species would be restricted to areas protected from management (e.g. riparian reserves). An uneven-aged system like single tree selection would be unlikely to eliminate the majority of the species with high value as wildlife foods. However, the 11 species with shade-intolerant regeneration would be likely to disappear unless natural disturbances created opportunities for their establishment. 4.3. Reliability of the analysis The ecological classi®cation presented in this paper, and our discussion of the relative compatibilities of different silvicultural systems with the management goals of the forest was intended to identify speci®c points of con¯ict between objectives for
211
maximizing timber production and for maintaining biodiversity within the managed forest. Our analysis for the species of LomerõÂo represents a ®rst attempt at evaluating the forest and is, in part, based on surmise and only preliminary data. Particularly lacking are reliable data with which tree species can be con®dently classi®ed by regeneration strategies. Much remains unknown about the ecology of sensitive vertebrate species in this forest. We considered only frugivores and were biased towards animals that are hunted. And while frugivores represent a large proportion of the mammal biomass in the forest (Guinart, 1997) and are thought to be sensitive to changes in forest structure and composition (Terborgh, 1986; Heydon and Bulloh, 1997), a more complete approach would be to consider a broader group species and type of plant±animal interactions. The large number of tree species identi®ed as important to frugivores suggests that they utilize a diverse food base. Unfortunately, we have little information about fruit phenologies, frugivore preferences, or nutritional qualities of the various species utilized by frugivores. Our classi®cation of tree species by their vulnerability to population declines in response to disturbance divided the species into two groups. The scores do not represent an absolute measure of vulnerability and must, therefore, be interpreted as only relative. Correlations between variables were generally lacking, suggesting that the four characteristics (shade tolerance, dispersal capacity, susceptibility to lianas and sensitivity to ®re) may not allow the species to be classi®ed into recognizable guilds. Our analysis assumes that it is preferable to employ silvicultural treatments that are compatible with the needs of wildlife. Despite application of the most suitable silvicultural treatments, some species are likely to be restricted to protected areas. For these species it will be important to consider how to best distribute protected zones within managed areas. Riparian forests are generally recognized as critical, but many questions remain as to how other areas should be ranked for protection. 5. Conclusions For a mixture of species with commercial potential, a silvicultural system can be designed and implemen-
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ted that is suitable for producing timber while maintaining the environmental conditions necessary for the maintenance of wildlife populations. Guarding against negative impacts of silviculture on food resources in managed forests alone will not insure the maintenance of wildlife populations; a distinct yet integrated management plan for wildlife is also needed (RumõÂz et al., in press.). Implementation of a mixed harvesting system will be technically more challenging than the current system of single tree selection or clearcutting. Particularly challenging will be tree marking and implementation of treatments to insure tree seedling establishment in felling gaps. Nevertheless, technical issues are not likely to be prohibitive if the system can be designed to be cost-effective. Very few large tracts of neotropical dry forests remain (Mooney et al., 1995). The Chiquitano forest in Bolivia, along with other dry forests in the Department of Santa Cruz, Bolivia, represent one of the largest remaining contiguous tracts of neotropical dry forest (Parker et al., 1993; Gentry, 1995); a management system that provides a continuous supply of timber while protecting biodiversity will be an important component of a conservation program for the region. Acknowledgements We thank O. Camacho, J. Fuentes, J. Huffman and S. Stanley for useful discussions about the forest of LomerõÂo. M.G. Barker and T. Killeen provided useful comments on an earlier draft of this manuscript. We also thank R. Aguape for sharing his data on reported fruit preferences of local wildlife, T. Killeen for assistace in the characterization of propagules, and F. Mamani for her assistance with species identi®cations and nomenclature. This work was funded by BOLFOR, a sustainable forest management project jointly funded by the Government of Bolivia and USAID. References Burton, P.J., Balisky, A.C., Coward, L.P., Cumming, S.G., Kneeshaw, D.D., 1992. The value of managing for biodiversity. For. Chronicle 68, 225±237.
Camacho, O., 1996. Analisis del impacto de aprovachamiento forestal en un bosque seco sub-tropical. Thesis presented to Autonomous University Gabriel Rene Moreno, Santa Cruz, Bolivia. Chandrashekara, U.M., Ramakrishnan, P.S., 1994. Successional patterns and gap phase dynamics of a humid tropical forest of the western Ghats of Kerala, India: Ground vegetation, biomass, productivity and nutrient cycling. For. Ecol. Manage. 70, 23±40. Ewel, J.J., L.F. Conde, 1980. Potential ecological impact of increased intensity of tropical forest utilization, BIOTROP Special Publication No. 11. Foster, R.B., 1982. The seasonal rhythm of fruitfall on Barro Colorado Island, In: Leigh, E.G., Rand, A.S., Windsor, D.M., (Eds.), The Ecology of a Tropical Forest, Smithsonian Institution Press, Washington, DC, pp. 151±172. Fox, J.E.D., 1976. Constraints on the natural regeneration of tropical moist forest. For. Ecol. Manage. 1, 37±65. Gentry, A.H., 1995. Diversity and floristic composition of neotropical dry forests, In: Bullock, S.H., Mooney, H.A., Medina, E., (Eds.), Seasonally Dry Tropical Forests, Cambridge University Press, Cambridge, UK, pp. 146±194. Goodman, L.A., Kruskal, W.H., 1954. Measures of association for cross-classification. J. Am. Stat. Assoc. 49, 732±764. Gottfried, G.J., 1983. Stand changes on a southwestern mixed conifer watershed after timber harvesting. J. For. 81, 311±316. Guinart, D., 1997. Los mamiferos del bosque semideciduo neotropical de LomerõÂo (Bolivia). Interaccion indigena. Ph.D. dissertation presented to University of Barcelona, Spain. Hammond, D.S., Brown, V.K., 1995. Seed size of woody plants in relation to disturbance, dispersal, soil type in wet neotropical forests. Ecology 76, 2544±2561. Hare, R.C., 1965. Contribution of bark to fire resistance of southern trees. J. For. 63, 248±251. Hartshorn, G.S., 1989. Application of gap theory to tropical forest management: Natural regeneration on strip clear-cuts in the Peruvian Amazon. Ecology 70, 567±569. Heydon, M., Bulloh, P., 1997. Mousedeer densities in a tropical rainforest: The impact of selective logging. J. Appl. Ecol. 34, 484±496. Holdsworth, A.R., Uhl, C., 1997. Fire in Amazonian selectively logged rain forest and the potential for fire reduction. Ecol. Appl. 7, 713±725. Ippore, B.J., 1996. Estudio de suelos en dos areas de accion forestal zona LomerõÂo, Proyecto BOLFOR, Santa Cruz, Bolivia. Killeen, T.J., Jardim, A., Mamani, F., Rojas, N., Saravia, P. In Review. A total quantitative floristic inventory of a 400 ha study site in the Chiquitano dry forest of eastern lowland Bolivia (LomerõÂo, Nuflo de Chavez, Santa Cruz, Bolivia), J. Trop. Ecol.. Killeen, T.J., Louman, B.T., Grimwood, T., 1990. La ecologõÂa paisajistica de la regioÂn de ConcepcioÂn y LomerõÂo en la Ä uflo de Chavez, Santa Cruz, Bolivia. EcologõÂa en provincia N Bolivia 16, 1±45. Leak, W.B., Filip, S.M., 1977. Thirty-eight years of group selection in New England northern hardwoods. J. For. 75, 641±643.
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213 Mamani, F., 1996. Inventario y riqueza floristica de un bosque seco pertenceciente a Las Trancas Y Puesto Nuevo, LomerõÂo, Provincia Nuflo de Chavez, Santa Cruz, Bolivia, Thesis presented to Universidad Autonoma Gabriel Rene Moreno, Santa Cruz, Bolivia. Marquis, D.A., 1965. Regeneration of birch and associated hardwoods after patch cutting. U.S. Forest Service Research Paper, NE-32. Martini, A.M.Z., De a. Rosa, N., Uhl, C., 1994. An attempt to predict which Amazonian tree species may be threatened by logging activities. Environmental Conservation 21, 152±162. Maser, C., 1994. Sustainable Forestry, Philosophy, Science, and Economics, St. Lucie Press, Delray Beach, FL, USA. Matthews, J.D., 1989. Silvicultural Systems, Oxford University Press, London, UK, 284pp. Meadows, J.S., Stanturf, J.A., 1997. Silvicultural systems for southern bottomland hardwood forests. For. Ecol. Manage. 90, 127±140. Meggers, B.J., 1987. The early history of man in Amazonia, In: Whitmore, T.C., Prance, G.T., (Eds.), Biogeography and Quaternary History in Tropical America, Clarendon Press, Oxford, UK, pp. 151±174. Mooney, H.A., Bullock, S.H., Medina, E. 1995. Introduction, In: Bullock, S.H., Mooney, H.A., Medina, E., (Eds.), Seasonally Dry Tropical Forests, Cambridge University Press, Cambridge, UK, pp. 1±8. Murphy, P.A., Shelton, M.G., Graney, D.L. 1993. Group selection ± Problems and possibilities and [sic] for the more shadeintolerant species, General Technical Report NC-161, U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. St. Paul, MN, USA. Nyland, R.D., 1996. Silviculture Concepts and Applications, McGraw-Hill, New York, USA, 633pp. Parker, T.A., Gentry, A.H., Foster, R.B., Emmons, L.H., Remsen, J.V. 1993. The Lowland Dry Forests of Santa Cruz, Bolivia: A Global Conservation Priority, Conservational International, Rapid Assessment Program, RAP Working Papers, No. 4, Washington, DC, USA. Pinard, M.A., Huffman, J., 1997. Fire resistance and bark properties of seasonally dry forest trees in Bolivia. J. Trop. Ecol. 13, 727±740.
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Pinard, M., Guzman, R., Fuentes, J. 1996. ClasificacioÂn de los gremios ecologõÂcos de las especies arboreas de LomerõÂo, BoletRn BOLFOR, 6: 2±4. BOLFOR, Proyecto de Manejo Forestal Sostenible, Santa Cruz, Bolivia. Putz, F.E., 1991. Silvicultural effects of lianas, In: Putz, F.E., Mooney, H.A., (Eds.), The Biology of Vines, Cambridge University Press, Cambridge, UK, pp. 493±501. RumõÂz, D.I., Guinart, D., Solar, L., Herrera, J.C., In press. Logging and hunting in community forests and corporate concessions: two contrasting case studies in Bolivia, In: Grajal, A., Fimbel, R., Robinson, J., (Eds.), Effects of Logging on Wildlife in the Tropics, Wildlife Conservation Society, New York, USA. Ryan, K.C., Reinhardt, E.D., 1988. Predicting postfire mortality of seven western conifers. Can. J. For. Res. 18, 1291±1297. Saville, D.J., 1990. Multiple comparison procedures: The practical solution. Am. Statistician 44, 174±180. Smith, D.M., 1986. The Practice of Silviculture, 8th edn., Wiley, New York, USA, 577pp. Stokes, B.J., Kluender, R.A., Williams, R.A., Klepac, J.F., 1993. Assessment of costs and impacts for alternative harvesting methods in mixed stands, Paper presented at the Seventh Biennial Southern Silvicultural Research Conference, Mobile, AL, USA, November 17±19, 1992. Terborgh, J., 1986. Keystone plant resources in the tropical forest. In: SouleÂ, M.E., (Ed.), Conservation Biology The Science of Scarcity and Diversity, Sinauer, Sunderland, MA, USA, pp. 330±344. Troup, R.S., 1952. Silvicultural Systems. Oxford University Press, London, pp. 216.. Uhl, C., Kauffman, J.B., Cummings, D.L., 1988. Fire in the Venezuelan Amazon. 2: Environmental conditions necessary for forest fires in the evergreen rainforest of Venezuela. Oikos 53, 176±184. Uhl, C., Kauffman, J.B., 1990. Deforestation, fire susceptibility, and potential tree responses to fire in the eastern Amazon. Ecology 71, 437±449. Wenger, K.F., 1984. Forestry Handbook, 2nd edn., Wiley, New York, pp. 418±419. Wilkinson, L., Hill, M., Welna, J.P., Birkenbeuel, G.K. 1992. Systat ± Statistics. SPSS Inc., Chicago, IL, USA.
Ecological characterization of tree species for guiding forest management decisions in seasonally dry forests in LomerõÂo, Bolivia M.A. Pinarda,c,*, F.E. Putzb, D. RumõÂzc, R. GuzmaÂnc, A. Jardimd b
a Department of Forestry, University of Aberdeen, Aberdeen AB24 5UA, UK Center for International Forestry Research (CIFOR), P.O. Box 6596, JKPWB, Jakarta 10065, Indonesia c Proyecto BOLFOR, Casilla #6204, Santa Cruz, Bolivia d Museo Noel Kempf Mercado, Casilla #2489, Santa Cruz, Bolivia
Received 13 October 1997; accepted 1 July 1998
Abstract When the goal of natural forest management is to maintain the biodiversity and ecological integrity of the forest while harvesting timber, the silvicultural systems employed must promote timber production and reduce negative impacts on nontimber resources. To foster development of such a system in a seasonally dry tropical forest in LomerõÂo, Bolivia, we classi®ed tree species according to their relative timber value, importance as food for vertebrate frugivores, and vulnerability to population declines when subjected to logging. We used this classi®cation to identify a management system appropriate for the commercial species and to evaluate the compatibility of the system with the regeneration requirements of tree species that produce important food for mammalian wildlife. About half of the tree species in the site are commercially valuable for their timber and a similar proportion are considered of value as food for wildlife. A tree species rating for vulnerability to disturbance appeared to be independent of both timber and wildlife values. A silvicultural system that includes even-aged groups of trees within an uneven-aged matrix appears more suitable to the multiple goals of management in this forest than either an even-aged or uneven-aged (single tree selection) management system. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Biodiversity; Bolivia; Harvesting systems; Logging; Natural forest management; Semi-deciduous tropical forest; Silviculture
1. Introduction Understanding the ecology of tree species is central to sustainable forest management and conservation. Most fundamentally, a species' regeneration requirements dictate, in part, which silvicultural systems are appropriate for its management (e.g. Smith, 1986). A *Corresponding author. Tel.: +44-1224-274110; fax: 44-1224272685; e-mail: [email protected]
species' ability to resprout after breakage, for example, may re¯ect its vulnerability to population declines in areas with selective logging (Martini et al., 1994). From a wildlife perspective, species that produce ¯eshy fruits during periods of general fruit scarcity may be of special importance due to their value as food for frugivorous mammals and birds (Foster, 1982; Terborgh, 1986). In this paper we consider the ecological characteristics of tree species in semi-deciduous forests of the
0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0378-1127(98)00426-5
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LomerõÂo region of Bolivia with the goal of identifying harvesting systems that enhance the regeneration of these species. In a mixed species forest, a single harvesting system will favor some species over others. If the goal of management is to maintain biodiversity and ecological integrity of the forest while harvesting timber, decisions need to be made about how to balance timber production against the associated negative impacts on the residual forest. To identify tree species likely to experience population declines as a consequence of timber harvesting, we use a set of characteristics to rate species on their vulnerability to disturbances. We test for correlations among ecological characteristics, timber values, and wildlife values to identify groups of species (or `guilds') within the forest community. Finally, we discuss the apparent compatibility of the recommended silvicultural system and maintenance of biodiversity in this forest. 1.1. Silvicultural issues Silvicultural systems generally involve the harvest of some trees followed by treatments to enhance regeneration, increase growth rates, or improve the quality of commercial trees within the residual forest. The harvesting (or tree selection) method used should be appropriate to the timber species' regeneration requirements, and whether or not the forest is to be maintained in even-aged or uneven-aged stands. A variety of harvesting systems is used in natural forest management (Table 1). The systems vary in the
degree of disturbance to the residual forest and differ in terms of the post-harvest habitats created for regeneration. For example, single tree selection methods result in relatively small felling gaps that foster development of shade-tolerant species and species represented by advanced regeneration (e.g. Gottfried, 1983; Stokes et al., 1993). Group tree selection methods result in larger felling gaps; within the center of these gaps, conditions may be appropriate for regeneration of shade-intolerant species (Hartshorn, 1989; Murphy et al., 1993; Meadows and Stanturf, 1997). Group selection results in aggregations of even-aged trees within an uneven-aged stand. In this study we recommend species for either evenaged or uneven-aged management based on their apparent requirements for, or tolerance of, shade during seedling establishment and development. We also discuss the suitability of particular felling systems (e.g. single tree selection, shelterwood; Table 1) for the commercial species as a group, considering timber values, potential for and environmental requirements of natural regeneration, abundance and distribution of mature trees, and the other goals of forest management. 1.2. Vulnerability to disturbance associated with timber harvesting Damage to residual trees, soil, and other non-timber resources during timber harvesting is variable and depends on environmental conditions during harvest,
Table 1 An outline of two basic timber management systems with examples of felling methods used for each system (Wenger, 1984; Matthews, 1989) Felling method Uneven-aged system Even-aged systems
Single tree selection Uniform clearcut Shelterwood Group tree selection Strip cuts
Features Remove some trees at relatively short intervals, maintaining an uneven-aged stand (i.e. one that contains a mixture of at least three distinct age classes within the forest). Mature trees, generally as scattered individuals, are removed during each harvest. Remove all or most trees during harvest and rely on new regeneration for producing the next even-aged stand. All trees on a site are removed in a single felling, relying on regeneration from artificial seeding, seed banks, seed rain from neighboring stands, or from planting; new crop is even-aged. Trees are removed in a series of cuts, the new stand is regenerated naturally or artificially under the old stand before all of the old stand is removed; new crop is even- or unevenaged. Groups of adjacent mature trees are removed during each harvest; new crop is regenerated naturally or artificially in the scattered gaps, and is even-aged. Trees are removed in strips; new crop within a strip is even-aged.
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
harvest intensity, felling methods used, and the care with which harvesting is carried out (e.g. Ewel and Conde, 1980). The selective extraction of timber from a forest, even where low impact techniques are used, causes damage to the residual stand. In areas where logging causes extensive structural damage and creates large felling gaps, tree species that regenerate in high light and are fast-growing, are likely to be favored by logging (Fox, 1976; Gottfried, 1983; Chandrashekara and Ramakrishnan, 1994) although competition with invading vines and other weeds may impede establishment (e.g. Putz, 1991). Alternately, populations of species that regenerate in shade may be vulnerable to severe logging disturbance. Certain ecological characteristics may be indicative of a species' vulnerability to population declines in timber harvesting areas. For example, in an analysis of Amazonian tree species, Martini et al. (1994) used the following characteristics to describe vulnerability: (1) long-distance seed dispersal ability; (2) sapling abundance; (3) ability to grow rapidly; (4) ability to resprout after cutting or breakage; (5) capacity to withstand ®re; (6) broadness of geographic range; and, (7) adult abundance. Other characteristics that may be useful include species regeneration strategies (e.g. seed longevity in soil), resistance to pathogens following damage, and susceptibility to lianas or herbivores. Given the large variability in forest composition and ecology found among tropical forests, the appropriate suite of characteristics useful for describing a tree species' vulnerability to disturbance will vary regionally. Based on our experience in this forest, we use bark thickness, susceptibility to lianas, capacity for seed dispersal, and shade tolerance of seedlings and saplings to predict relative vulnerability to disturbance. 1.3. Management objectives Many forest managers are striving to identify ways to manage forests for timber while protecting the biological and physical resources of the forests; these resources include biodiversity, water quality, soil conservation, and ecological functions (e.g. Burton et al., 1992; Maser, 1994). This goal of managing for timber while maintaining biodiversity presents potentially con¯icting objectives. Development of suitable management plans will require decisions regarding trade-
203
offs between activities that maximize timber production and those that reduce negative impacts on the biological integrity of the system. In this paper we consider the silvicultural needs of commercial tree species and the compatibility of felling systems with the regeneration requirements of non-timber tree species and maintenance of tree species diversity in a tropical dry forest in Bolivia. 2. Methods 2.1. Study site The semideciduous forests of LomerõÂo are in the Ä u¯o de Chavez, Santa Cruz, Bolivia Province of N 0 (16845 S, 618450 W) at an elevation of 400±600 m. Mean annual rainfall is 1130 mm and mean temperature 248C (ConcepcioÂn Meteorological Station, cited in Killeen et al., 1990). The region is characterized by its undulating topography and the vegetation, a mosaic of natural savanna and dry-to-subhumid forest. Soils are described as well-drained Inceptisols, Al®sols (Killeen et al., 1990), and Oxisols (Ippore, 1996). Mean forest canopy heights are 12±18 m with emergent trees to 30 m. Total basal area for trees >10 cm dbh averages about 23 m2 haÿ1. About 140 tree species have been recorded with 19±27 species found per hectare (Killeen et al., 1990). About 60% of total basal area (trees >10 cm dbh) is composed of legumes. Much of the forest of LomerõÂo is within the community lands of an indigenous group, the Chiquitanos. The objective of the current management plan for the forests of LomerõÂo is to sustainably produce timber while minimizing negative impacts on the other biological and physical resources in the forest. The Chiquitanos rely heavily on wild meat to supplement their protein intake; consequently, a silvicultural system that maintains critical habitats for large mammals is of particular interest. Three of the 15 timber tree species currently being harvested are considered high value, relative to other marketable timbers in the country, and are saleable on international markets. The remaining 12 species had relatively low value in Bolivia at the time of the study (1996), though some of these species are considered of high value in other Latin American countries. Forestry operations of Chiquitano communities were certi®ed as sustainable by
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SmartWood in 1995, thus the possibility of entering green markets exists and may increase sale values and market access for some of the lesser known species. Timber harvest activities are restricted to the dry season (May±October) and are implemented in 400 ha blocks. Log extraction routes are opened by hand and a farm tractor is used for skidding logs to a loading area. Logging intensity ranges from 2 to 5 trees haÿ1 (3±10 m3 haÿ1). Damage to the residual stand is principally in the form of small felling gaps, skid trails, and roads. Roads and skid trails cover only 2±4% of the site and felling gaps are generally only 40±70 m2 (Camacho, 1996). The logs are sawn in a communityowned mill and the lumber is then transported by truck 8±10 h to Santa Cruz for sale. The natural disturbance regime for this forest is likely to include infrequent disturbance related to droughts and ®re or slash and burn agriculture. Low-intensity ground ®res occur frequently in the savannas bordering the forests of LomerõÂo but it is unclear how frequently ®res penetrate the forests. The predominance of relatively thin-barked canopy species suggests that the forest characteristic of the region, at present, did not develop with frequent ®res (Pinard and Huffman, 1997). Recorded human occupancy of the region dates only to the 1700s (Killeen et al., 1990); however, it is likely that humans have occupied the region much earlier (Meggers, 1987). Logging may increase the forest's vulnerability to ®re through changes in microclimate and fuel loads (Uhl et al., 1988; Uhl and Kauffman, 1990; Holdsworth and Uhl, 1997). As part of a larger, integrated forest management project, 100 permanent plots (2050 m2) were established following a strati®ed random design in a 400 ha block of forest in 1994 for describing forest structure and composition prior to logging (Mamani, 1996; Killeen et al., in review). All tree species that obtain a dbh of 15 cm were included in the analysis. Small stature species (maximum tree sizes of <30 cm dbh) may not be commercially viable for timber but, because they represent a signi®cant proportion of the diversity (25 of 69 arboreal species) in the forest, we included them in the study (hereafter, subcanopy species). Within each plot, trees >=20 cm dbh were identi®ed to species and dbh and grade of infestation of lianas was recorded (1no lianas present; 2one to few lianas on stem; 3few lianas in crown; 4lianas
covering crown). Nested subplots (2025 m2 and 1010 m2) were established within each plot and the number of saplings (10±20 cm dbh, and 5± 10 cm dbh) by species were recorded, respectively. Commercial status and timber values were based on the timber markets in Santa Cruz, Bolivia (A. Guillen, pers. comm.). Species were classi®ed by the importance of their fruits for local mammal and bird species, based on interviews with local hunters and stomach contents of game taken by these hunters (Guinart, 1997; R. Aguape, unpubl. data). 2.2. Selection of characters ± Silvicultural considerations Of the range of possible characteristics for describing the ecology of tree species in the study area, we selected those that represent the union of characteristics that we considered useful and those for which we had reliable data (Table 2). A general classi®cation by shade tolerance was used to match silvicultural systems with regeneration requirements of the species. We classi®ed tree species on the basis of their regeneration requirements (hereafter, shade tolerance class) for light or tolerance of shade based on ®eld observations, some as yet unpublished physiological studies, interviews with local foresters, and references to the literature (Pinard et al., 1996). We used three tolerance classes and assigned each a score as follows: (1) species that have relatively light demanding regeneration requirements and establish on forest edges or in large gaps (>200 m2); (2) species that can establish in canopy gaps of various sizes but also in the forest understory; and, (3) species with seed that germinates in the shade and seedlings that are shade-tolerant. Five of the 61 species could not be matched to a shade tolerance class because of lack of information. 2.3. Selection of characters ± Vulnerability to disturbance To classify the species in terms of their vulnerability to disturbance, we used the following characteristics: bark thickness; seed dispersal capacity; shade tolerance; and resistance to lianas (Table 2). Although many other characteristics are potentially important and useful, we limited ourselves to characteristics for which we had data. Adult tree abundance was not
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
205
Table 2 Ecological characteristics used to determine species' vulnerability to population declines in areas with disturbance associated with timber harvesting Characteristics
Score1
Score2
Score3
Shade tolerance of regeneration Susceptibility to fireb Inverse of capacity for propagule disperalc Susceptibility to invasion by lianasd Adult tree raritya Sapling rarity (5±10 cm dbh)e
High light only, large gaps Resistant (>18 mm) High capacity Low (20%) Common (>5 haÿ1) Common (20 haÿ1)
Partial shade, small gaps Intermediate (10±18 mm) Intermediate capacity Medium (between 20 and 45%) Intermediate (1±5 haÿ1) Intermediate (5±20 haÿ1)
Partial or full shade, understory Sensitive (<10 mm) Low capacity High (45%) Rare (<1 haÿ1) Rare (<5 haÿ1)
Adult treea and sapling rarity characteristics were not included in the calculation of vulnerability; they are included here and assigned a score to allow for an analysis of correlations between characteristics. a Trees >20 cm dbh, unless noted as subcanopy trees considered adults when >10 cm dbh. b Based on bark thickness for canopy trees 20 cm dbh, subcanopy trees 10±15 cm dbh. c Based on propagule size, presence/absence of wings, and whether or not it is animal-dispersed (see text). d Percentage of adult trees with lianas on stem and in crown (grades 3 and 4). e For palms, plants were considered saplings if they were stemless but had leaves >2 m long.
included because species may be rare due to lack of disturbance. Bark thickness was included as an indication of a species' ®re tolerance (Hare, 1965; Ryan and Reinhardt, 1988; Pinard and Huffman, 1997). We measured bark thickness (at 0.5±1.3 m) on trees 15± 25 cm dbh; N3±10 individuals per species. Thirteen species lacked bark thickness data. Bark thickness classes are based on studies of bark thermal properties of 16 local species that indicate 18 mm thickness as the threshold or minimum thickness for a tree to withstand low intensity ground ®res (Pinard and Huffman, 1997). Our classi®cation of seed dispersal capacity is based on propagule size and the presence or absence of structures to assist dispersal (e.g. hairs, wings, ¯esh). Although seed size is related to dispersal mode (Hammond and Brown, 1995), the negative correlation between dispersal distance and propagule size is not strong; many species have relatively large propagules but also possess structures that increase the likely distance of dispersal. Based on herbarium material and discussions with local botanists, we scored the species' propagules, by volume (1 for small, <50 mm3; 2 for medium, 50±1000 mm3; 3 for large, >1000 mm3), and then subtracted 1 from the score if the propagule possessed a wing, hairs or pappus, a ¯eshy exocarp, or an aril. Thus, the lower the score, the better the predicted dispersal capacity. Susceptibility to lianas was estimated as the proportion of adult trees in the study area that had lianas in their crowns. Susceptibility was considered low
when less than 20% of trees had lianas in their crowns (score1), and high when greater than 45% of trees had lianas in their crowns (score3). The intermediate condition was scored 2 (Table 2). We further scored species by the rarity of adult trees and saplings (5±10 cm dbh) into three groups: common; intermediate; or, rare (Table 2). Although the minimum diameter for fruit production varies with species and environmental conditions, we considered trees above a threshold diameter to be capable of producing fruits. For species that reach dbh >=40 cm, individuals >=20 cm dbh were considered adults; for species that reach maximum dbh of less than 30 cm dbh, individuals >=10 cm were considered adults. 2.4. Data analysis A vulnerability score was calculated for each species based on the mean of the four contributing characters (shade tolerance, resistance to lianas, seed size, bark thickness). We used a mean rather than a sum because for some species (N13), we were unable to assign a species score for all characteristics. Larger scores re¯ect a higher vulnerability to disturbance. ANOVA followed by pairwise comparisons (Least Squares Difference, Saville, 1990) were used to compare vulnerability scores for timber and wildlife value classes. To identify correlations among the ecological characteristics, we conducted a correlation analysis using Goodman±Kruskal -coef®cients for
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M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
ordinal data (Goodman and Kruskal, 1954 cited in Wilkinson et al., 1992). 3. Results 3.1. General classification Only 108 of the 140 tree species found in the semideciduous forests of LomerõÂo, were recorded in our 400 ha study site. Of these, 69 species obtained diameters of at least 15 cm and were classi®ed on the basis of their ecological characteristics (Table 3). Based on market conditions at the time of the analysis, 31 of the 69 species were considered of commercial value for their timber (Table 4). Of the commercial species, 11, representing 15% of total basal area, had a relatively high value and 20 species, or 65% of total basal area, had a relatively low value. The 38 species that were considered to have no commercial timber value represented only about 20% of the total basal area (trees >10 cm dbh). Twenty species were considered of high value for vertebrate frugivores; these species represented 9% of the basal area (Table 4). Generally, the more abundant tree species were considered of low value to frugivores. The 15 tree species of intermediate value to frugivores represented about 16% of the basal area. 3.2. Silvicultural systems Species were matched to a general silvicultural system (even- or uneven-aged management) based on their regeneration requirements. For species with shade-tolerant regeneration requirements (scores 2 and 3), we suggest uneven-aged management with a single-tree selection harvest system. For species with shade-intolerant regeneration (score 1), we suggest even-aged management. Rather than assign each species to a particular felling system within even- or uneven-aged management, we discuss the suitability of major felling systems for the group of commercial species. Based on seedling shade tolerance, half of the commercial timber species at the site appear compatible with even-aged management, and half compatible with uneven-aged management. In terms of total basal area, 37 and 43%, respectively, were commercial
and compatible with even- and uneven-aged management (Table 5). When all species were considered, 36% appeared compatible with even-aged management and 59% compatible with uneven-aged management (score 3 could not be classi®ed). For the species considered of high value to wildlife, the classi®cation was 19 and 81% for even- and uneven-aged management, respectively (Table 5). 3.3. Vulnerability On a scale of 1±3 representing increasing vulnerability to disturbance, scores ranged from 1.00 to 2.75 (median2.00, N69; Table 6). The scores had a bimodal distribution suggesting two distinct groups of species, the ®rst with relatively low vulnerability and a mean score of 1.65 (N38), the second, with relatively high vulnerability and a mean score of 2.51 (N30; Fig. 1). Using the division of species into two groups based on vulnerability scores, the number of species classi®ed with low and high vulnerability was independent of both the species importance for wildlife (X20.84, d.f.2, p0.66) and value for timber (X20.98, d.f.2, p0.61). 3.4. Correlations among variables The four characteristics used for assessing vulnerability to disturbance are not strongly correlated with one another. The strongest association observed was between shade tolerance and susceptibility to ®re (Table 7); thin-barked species tended to have shadetolerant regeneration. Shade tolerance was weakly negatively correlated with capacity for dispersal (i.e. greater shade tolerance was associated with poorer dispersal). Tree and sapling rarity were positively correlated. Sapling rarity was negatively correlated with shade tolerance, indicating that the least abundant sapling species were relatively light demanding. Adult tree rarity, however, was not correlated with shade tolerance; species with shade-tolerant and species with shade-intolerant regeneration strategies were equally represented among the more common overstory species (Table 7). Timber values were negatively correlated with wildlife values, and weakly negatively correlated with shade tolerance.
Low Low Inter Low Inter Low Low Low Inter Low Low High Low Low Low Low High Inter Low Low High High Low Inter Low Inter High Low Low High High Low Inter Low Inter Inter
Family
Mimosaceae Caesalpinioideae Caesaplinioideae Apocynaceae Bombaceae Mimosaceae Bignonaceae Fabaceae Bombaceae Fabaceae Anacardiaceae Caesalpinioideae Apocynaceae Ulmaceae Phytolaccaceae Anacardiaceae Palmae Lecythidaceae Fabaceae Combretaceae Flacourticeae Capparadaceae Rubiaceae Nyctaginaceae Nyctaginaceae Fabaceae Anacardiaceae Meliaceae Polygonaceae Moraceae Moraceae Papilionoideae Bombacaceae Papilionoideae Nyctaginaceae Bombaceae
Tree species
Anadenanthera colubrina (Vell.) Brenan Poeppigia procera C. Presl Caesalpinea floribunda Tul. Aspidosperma rigidum Rusby Chorisia speciosa St. Hilaire Acacia polyphylla DC. Tabebuia impetiginosa (Mart. ex DC) Standl. Centrolobium microchaete Lima ex G. P. Lewis Eriotheca roseorum (Cuatr.) Meyer Machaerium scleroxylon Tul. Astronium urundeuva (Fr. Allemao) Engler Peltogyne heterophylla M. de Silva Aspidosperma cylindrocarpon Muell. Arg. Phyllostylon rhamnoides (Poisson) Taub. Gallesia integrifolia (Sprenge) Hams Schinopsis brasilensis Engl. Scheelea princeps (C. Martius) G Karsten Cariniana estrellensies (Raddi) Kuntze Machaerium acutifolium Vogel Combretum leprosum Mart. Casearia gossipiosperma Briq. Capparis prisca J F Macbr. Simira rubescens(Benth.) Steyerm. Neea anisophylla Ernst Bougainvillea modesta Hiermerl Platypodium elegans Vog. Spondias mombin L. Cedrela fissilis Vell. Ruprechtia laxifolia Meisner Sorocea sprucei (Baippon) Macbr. ssp. saxicola Hassler C.C. Berg. Ficus gomelleira Kunth and Boucher Cyclobium blanchetianum Tul. Ceiba samauma (Mart.) Schum. Amburana cearensis (Allemao) A.C. Smith Neea hermaphrodita S. Moore Uel Pseudobombax marginatum (St. Hilaire) Rubyns Low None None High None None
None High Low High Low Low None Low None Low Low None Low None None None Low None None High None None
Low Low Low Low None Low High High
Even Even Uneven Even
Even
Even Uneven Even Uneven Uneven Uneven Uneven Even Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Uneven Even Even Uneven
Even Uneven Uneven Uneven Even Uneven Even Even
3 3 2 3 1 3
2 1 2 2 2 2 2 2 2 2 1 2 1 1 1 1 2 2 2 3 2 3
1 1 1 1 1 1 1 1
3 3 3 3 1 3
3 2 3 3 3 2 2 3 3 2 2 2 1 2 1 2 3 3 3 3 3 3
2 1 2 2 2 2 3 3
1 1 3 1
1
1 3 1 3 2 3 3 1 2 3 3 2 3 3 3 3 2 3 2 1 1 3
1 3 2 2 1 2 1 1
1 1 1 1 2 1
1 2 1 1 2 2 1 1 1 1 2 1 1 1 1 2 1 2 2 1 2 1
2 2 2 2 1 1 1 2
2 3 3 1
3
1 3 2 3 1 3 3 1 1 1 2 3 3 3 3 3 3 2 1 1
2 3 2 1 1 3 2 3
3 2 3 2 3 3
3 3 2 3 3 3 3 2 1 2 3 3 3 3 3 3 3 3 1 3 1 1
2 3 3 2 3 3 3 3
2.00 1.50 1.75 1.75 2.75 1.50
1.50 2.75 1.50 2.50 2.00 2.75 2.50 1.25 1.25 1.75 2.50 2.25 2.50 2.50 2.50 2.75 2.25 2.50 1.50 1.50 1.33 1.67
1.75 2.75 2.25 1.75 1.50 2.25 1.75 2.25
0.115 0.115 0.112 0.096 0.096 0.059
0.735 0.714 0.690 0.663 0.558 0.499 0.467 0.435 0.392 0.320 0.307 0.230 0.196 0.186 0.159 0.154 0.150 0.129 0.129 0.125 0.123 0.119
5.199 3.380 1.045 0.961 0.946 0.929 0.861 0.763
Inverse of Susceptibility Susceptibility Vulnerability Basal Wildlife Timber Management Adult Sapling Shade to fire to Lianas score area value value system rarity rarity tolerance of capacity regeneration for dispersal
Table 3 Characteristics of tree species of the semideciduous forests of LomerõÂo
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213 207
Low High Low High High Low Low Inter Low High Low Inter High High High High Low High Inter Low Inter Low
Papilionoideae Mimosoideae Papilonoideae Sapotaceae Urticaceae Tiliaceae Combretaceae Bignoniaceae Vochysiaceae Hippocrataceae Rubiaceae Bignoniaceae Nyctaginaceae Moraceae Mimisoideae Humiriaceae Fabaceae Annonaceae Moraceae Tiliaceae Opiliaceae Fabaceae
Low Low None None None None Low None None None None High None None None None Low None None None None High
None Low None None High None High Low None None
Even
Uneven Uneven Uneven Even Uneven Even Even Uneven Uneven Uneven Even Uneven Even Uneven Uneven Uneven Uneven Uneven Even
Uneven Uneven Uneven Uneven Even Uneven Even Even Uneven Even 2 3 3 3 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
3 3 3 3 3 2 2 3 3 3 3 3 3 3 2 2 3 3 3 3 3 3 3 3 3 3 3 2 3 3 3 3
3 2 3 2 2 3 3 3 3 3
1
3 2 3 1 2 1 1 3 3 3 1 3 1 3 3 3 3 3 1
3 2 3 3 1 3 1 1 3 1
1 1 1 1 1 1 1 2 1 2 1 1 2 2 1 1 1 1 2
1 2
1 2 1 1 2 2 1 2 2 2
1
3
3
2 3 2 3 3
3 3 3 2 1
3
3
1 1 2 3 1 3
3 3 1 3 3 3 1 3 3 3 1 3 1 3 3 3 1 1 3
2 2
1 3 3 3 1 3 3 3 3 3 1.50 2.50 2.00 2.50 2.00 1.75 1.75 1.50 2.33 1.75 2.75 1.75 2.75 1.50 2.33 2.00 2.75 2.33 2.33 1.50 1.00 1.75
1.50 2.00 2.25 2.50 1.25 2.75 1.67 2.00 2.75 2.00
0.026 0.026 0.023 0.022 0.020 0.019 0.016 0.016 0.015 0.013 0.011 0.011 0.010 0.009 0.007 0.006 0.006 0.005 0.005 0.004 0.004 0.004
0.057 0.053 0.050 0.049 0.041 0.041 0.039 0.038 0.031 0.029
Species are listed by basal area (trees 10 cm dbh). See text and Table 2 for definitions of the scores (0±3) for the characteristics. The management system is based on shade tolerance of regeneration, even-aged management is recommended for score 1, uneven-aged management is recommended for scores 2 and 3. When no shade tolerance score was assigned, no management system was assigned. Vulnerability score per species was calculated as the mean of scores for shade tolerance, susceptibility to lianas, capacity for propagule dispersal, and bark thickness.
High Low High High Low High Inter High Inter Low
Palmae Apocynanceae Verbenaceae Meliaceae Boraginaceae Annonaceae Lauraceae Caesalpinioideae Nyctaginaceae Polygonaceae
Syagrus sancona Karsten Aspidosperma pyrifolium Mart. Vitex cymosa Bert. Trichilia elegans A. Juss. Cordia alliodora (r. & P.) Cham. Annona cf. jahnii Saff. Ocotea cf. cernua (Nees) Mez Hymenaea courbaril L. Neea cf. ovalifolia Spruce ex J A Schmidt Ruprechtia salicifolia (Cha. et Schlecht.) Meyer Lonchocarpus guillemineanus (Tul.) Malme Inga marginata Willd. Andira inermis (Wright) DC Pouteria gardneriana (A.DC.) Rudlk. Urera baccifera (L.) Gaudich Luehea candicans Mart. Terminalia oblonga (Ruiz and Pavon) Steud. Zeyheria tuberculosa (Vell.) Bur. Callistene sp. Salacia elliptica (Mart.) G. Don Pogonopus tubulosus DC Schumann Tabebuia serratifolia (Vahl.) Nichols Pisonia sapallo Griseb. Cecropia concolor Willd. Samanea saman (Jacq.) Merr. Sacoglottis mattogrosensis Malme Machaerium jacarandifolium Rusby Duguettia guitarensis Benth. Maclura tinctoria (L.) Steud. Heliocarpus americanus L. Agonandra brasilensis Miers Platymiscium ulei Harms
Inverse of Susceptibility Susceptibility Vulnerability Basal Wildlife Timber Management Adult Sapling Shade to fire to Lianas score area value value system rarity rarity tolerance of capacity regeneration for dispersal
Family
Tree species
Table 3 (continued )
208 M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213 Table 4 Summary data for 69 tree species in LomerõÂo Characteristic
Category
Species
Basal area
Wildlife value
1 2 3 1 2 3
33 15 21 38 20 11
17.07 3.70 2.16 4.60 14.95 3.38
Timber value
± ± ± ± ± ±
low intermediate high none low high
(48%) (22%) (30%) (55%) (29%) (16%)
(74%) (16%) (9%) (20%) (65%) (15%)
For each category of wildlife and timber values, total number of species and basal area (percentages noted in parenthesis) per category.
209
Table 6 Vulnerability scores for tree species by category of wildlife and timber value Characteristic
Category
Wildlife value
1 2 3 1 2 3
Timber value
± ± ± ± ± ±
Vulnerability score
low intermediate high none low high
2.00 1.95 2.12 2.04 2.09 1.88
(0.48, (0.56, (0.45, (0.52, (0.45, (0.44,
33) 15) 21) 38) 20) 11)
Mean (SD, N) scores are presented for each category.
Table 5 Classification of tree species by recommended timber management system (even-aged or uneven-aged) and by category of wildlife and timber value Characteristic
Wildlife value Timber value
Category
1 2 3 1 2 3
± ± ± ± ± ±
low intermediate high none low high
Basal area (m2 haÿ1)
Species Even
Uneven
Even
Uneven
14 7 4 10 6 9
17 7 17 26 13 2
8.5 1.9 0.2 2.0 6.5 2.0
8.5 1.8 2.0 2.4 8.4 1.4
Total number of species and total basal area are presented for each combination of categories.
Fig. 1. Frequency histogram with vulnerability scores for 69 tree species in LomerõÂo. Higher scores represent an increased likelihood of population declines due to disturbances during timber harvest.
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M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
Table 7 Goodman±Kruskal -correlation coefficients between pairs of tree species characteristics (N55)
Shade tolerance Susceptibility to Lianas Capacity for dispersal Susceptibility to fire Adult tree rarity Sapling rarity Wildlife value Timber value
Shade tolerance
Susceptibility to Lianas
Capacity for dispersal
Susceptibility to fire
Adult tree rarity
Sapling rarity
Wildlife value
0.27 0.45 0.57 ÿ0.21 ÿ0.49 0.39 ÿ0.43
0.25 0.40 ÿ0.28 ÿ0.26 ÿ0.11 0.11
0.01 ÿ0.23 ÿ0.25 ÿ0.38 0.36
ÿ0.19 ÿ0.37 0.13 ÿ0.22
0.83 0.26 ÿ0.09
0.29 0.06
ÿ0.66
Scores assigned to characteristics are defined in Table 2.
4. Discussion The two goals for this study were: (1) to identify a timber stand management system appropriate for the commercial species in our study site in Bolivia; and, (2) to evaluate the compatibility of the recommended system with the regeneration requirements of tree species that produce fruit of particular importance to wildlife. Based on the results of the ecological characterization of commercial species, we recommend a silvicultural approach that combines even- and uneven-aged management. By incorporating single tree and group selection in a spatial mosaic, conditions appropriate for the regeneration of both shade-intolerant and shade-tolerant species could be maintained within the management unit. A mixed system appears more compatible with maintenance of wildlife food species than does the uniform application of either even- or uneven-aged management. 4.1. Silvicultural system Although the high value timber species (N11) in LomerõÂo appear to have ecologies compatible with even-aged management, the commercial species considered as a group (N31) include a broad range of seedling shade tolerance. From the timber producer's perspective, it seems more appropriate to focus on the entire group of commercial species than just on a few high value species because high value species alone currently represent only a small proportion of the available mature timber. Management for the entire group of commercial species requires a silvicultural approach that provides
conditions appropriate for species with shade-tolerant seedlings as well as for species that regenerate only in large clearings. This approach could be developed by mixing two regeneration systems spatially. A spatial mixture might be achieved by felling groups of trees to create scattered gaps, strips, or patches, and by felling single trees in the remainder of the forest matrix (i.e. patch selection method, Leak and Fillip, 1977; Nyland, 1996). This type of mixture has been successfully used for managing bottomland hardwood forests in the southeastern US (Meadows and Stanturf, 1997). The size of the openings made from group felling would need to be matched to the regeneration requirements of the shade-intolerant species (e.g. Marquis, 1965). Narrow strips and gaps >=0.5 ha may provide environmental conditions appropriate for very shadeintolerant species only in the center of the openings. A patch selection approach may be a reasonable simulation of the natural stand dynamics in the forest. While both shade-tolerant and light-demanding species are intimately mixed in the stands, some of the light-demanding species (e.g. Cedrela; Astronium) have clumped distributions that may coincide with old agricultural clearings or hot spots in past ®res. In the seasonally dry forest of LomerõÂo, fruitfall tends to be during the dry season (Bolfor, unpubl. data) and the seeds of many tree species tend to remain in the seed bank only until the rain season commences (Pinard, unpublished data). To achieve suf®cient seedling establishment in large openings, it is likely that natural regeneration would need to be assisted by broadcast seeding or other enrichment treatments. As long as damage to advanced regeneration is controlled in areas kept in uneven-aged stands, probably
M.A. Pinard et al. / Forest Ecology and Management 113 (1999) 201±213
natural regeneration would be suf®cient to maintain recruitment. An alternative to a patch selection system would be an irregular shelterwood system (Troup, 1952). Irregular shelterwoods are used in Germany and Switzerland to favor both shade-intolerant and shade-tolerant species in the same stand (Matthews, 1989). This approach involves a succession of regeneration fellings with long, inde®nite regeneration periods; the application in Europe generally targets two-to-®ve species. The application of an irregular shelterwood system in the Chiquitano forest where 31 species have commercial timber value may not be practical or ®nancially viable given the need for frequent and scattered stand intervention, the lack of information about species growth rates, and the relatively heavy thinning that would be required to regenerate the more light-demanding species. 4.2. Compatibility of the silvicultural system with maintenance of wildife food production When compared to either a uniform application of even- or uneven-aged management (single tree selection), a mixed system is probably the most compatible with the multiple goals of forest management in LomerõÂo. Application of a uniform even-aged management system would be aimed at creating a forest dominated by light-demanding species with high timber value. In this site, species with high timber value tend to be of low value to wildlife. If the management system were effectively implemented, the majority of the wildlife food species would be restricted to areas protected from management (e.g. riparian reserves). An uneven-aged system like single tree selection would be unlikely to eliminate the majority of the species with high value as wildlife foods. However, the 11 species with shade-intolerant regeneration would be likely to disappear unless natural disturbances created opportunities for their establishment. 4.3. Reliability of the analysis The ecological classi®cation presented in this paper, and our discussion of the relative compatibilities of different silvicultural systems with the management goals of the forest was intended to identify speci®c points of con¯ict between objectives for
211
maximizing timber production and for maintaining biodiversity within the managed forest. Our analysis for the species of LomerõÂo represents a ®rst attempt at evaluating the forest and is, in part, based on surmise and only preliminary data. Particularly lacking are reliable data with which tree species can be con®dently classi®ed by regeneration strategies. Much remains unknown about the ecology of sensitive vertebrate species in this forest. We considered only frugivores and were biased towards animals that are hunted. And while frugivores represent a large proportion of the mammal biomass in the forest (Guinart, 1997) and are thought to be sensitive to changes in forest structure and composition (Terborgh, 1986; Heydon and Bulloh, 1997), a more complete approach would be to consider a broader group species and type of plant±animal interactions. The large number of tree species identi®ed as important to frugivores suggests that they utilize a diverse food base. Unfortunately, we have little information about fruit phenologies, frugivore preferences, or nutritional qualities of the various species utilized by frugivores. Our classi®cation of tree species by their vulnerability to population declines in response to disturbance divided the species into two groups. The scores do not represent an absolute measure of vulnerability and must, therefore, be interpreted as only relative. Correlations between variables were generally lacking, suggesting that the four characteristics (shade tolerance, dispersal capacity, susceptibility to lianas and sensitivity to ®re) may not allow the species to be classi®ed into recognizable guilds. Our analysis assumes that it is preferable to employ silvicultural treatments that are compatible with the needs of wildlife. Despite application of the most suitable silvicultural treatments, some species are likely to be restricted to protected areas. For these species it will be important to consider how to best distribute protected zones within managed areas. Riparian forests are generally recognized as critical, but many questions remain as to how other areas should be ranked for protection. 5. Conclusions For a mixture of species with commercial potential, a silvicultural system can be designed and implemen-
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ted that is suitable for producing timber while maintaining the environmental conditions necessary for the maintenance of wildlife populations. Guarding against negative impacts of silviculture on food resources in managed forests alone will not insure the maintenance of wildlife populations; a distinct yet integrated management plan for wildlife is also needed (RumõÂz et al., in press.). Implementation of a mixed harvesting system will be technically more challenging than the current system of single tree selection or clearcutting. Particularly challenging will be tree marking and implementation of treatments to insure tree seedling establishment in felling gaps. Nevertheless, technical issues are not likely to be prohibitive if the system can be designed to be cost-effective. Very few large tracts of neotropical dry forests remain (Mooney et al., 1995). The Chiquitano forest in Bolivia, along with other dry forests in the Department of Santa Cruz, Bolivia, represent one of the largest remaining contiguous tracts of neotropical dry forest (Parker et al., 1993; Gentry, 1995); a management system that provides a continuous supply of timber while protecting biodiversity will be an important component of a conservation program for the region. Acknowledgements We thank O. Camacho, J. Fuentes, J. Huffman and S. Stanley for useful discussions about the forest of LomerõÂo. M.G. Barker and T. Killeen provided useful comments on an earlier draft of this manuscript. We also thank R. Aguape for sharing his data on reported fruit preferences of local wildlife, T. Killeen for assistace in the characterization of propagules, and F. Mamani for her assistance with species identi®cations and nomenclature. This work was funded by BOLFOR, a sustainable forest management project jointly funded by the Government of Bolivia and USAID. References Burton, P.J., Balisky, A.C., Coward, L.P., Cumming, S.G., Kneeshaw, D.D., 1992. The value of managing for biodiversity. For. Chronicle 68, 225±237.
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