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Establishment, growth and biomass production of 10 tree woody species introduced for reforestation and ecological restoration in northeastern Mexico
Forest Ecology and Management 235 (2006) 194–201 www.elsevier.com/locate/foreco
Establishment, growth and biomass production of 10 tree woody species introduced for reforestation and ecological restoration in northeastern Mexico R. Foroughbakhch *, M.A. Alvarado-Va´zquez, J.L. Herna´ndez-Pin˜ero, A. Rocha-Estrada, M.A. Guzma´n-Lucio, E.J. Trevin˜o-Garza Departamento de Bota´nica, Facultad de Ciencias Biolo´gicas, Universidad Auto´noma de Nuevo Leo´n, Box 2-F, Cd. Universitaria, San Nicola´s de los Garza, NL 66451, Mexico Received 15 February 2006; received in revised form 10 August 2006; accepted 10 August 2006
Abstract The coast of the Gulf of Mexico is characterized as a region with high variation in climatic conditions and rich in drought-tolerant or subhumid species. The species that are potentially useful for reforestation, regreening, agroforestry activities and the production of timber and fuelwood have been overexploited, resulting in a gradual decrease and degradation of their populations. In order to restore the soil and rehabilitate the disturbed areas inhabited by matorral vegetation, we tested the adaptability, development and establishment of 10 introduced tree species. The species were: Albizia caribaea Britton & Rose, Albizia guachapele (H.B. & K.) Dugand, Caesalpinia velutina (Britton & Rose) Standl., Caesalpinia eriostachys Benth., Crescentia alata H.B. & K., Enterolobium cyclocarpum Griseb., Gliricidia sepium (Jacq.) Steud., Haematoxylon brasilleto Karst., Myrospermum frutescens Jacq. and Pithecellobium dulce (Roxb.) Benth. The seeds of each species received different pretreatments. Seedlings were grown in plastic bags and planted out after 6 months by hand in August 1985 in a monoculture in four randomized blocks in a cleared area with deep loamy-clay soil, slightly alkaline. Measurements of different growth parameters and leaf/twig biomass over 15 years were evaluated. The species C. alata, E. cyclocarpum, G. sepium and H. brasilleto tended to have better characteristics in terms of growth annual rate (33–62 cm in height and 1.7–2.6 cm in basal diameter during 1985–1990), while A. caribaea, A. guachapele, C. velutina y C. eriostachys (20–30 cm in height and 1.2–1.7 cm in basal diameter) did not establish well due to susceptibility to frost. M. frutescens and P. dulce had intermediate yields of great interest due to their multipurpose potential. The linear models gave a better estimate of tree biomass than the logarithmic functions. The species with the highest determination coefficient (r2) and the lowest mean square error (MSE), were E. cyclocarpum (r2 = 0.96; MSE = 19.8), G. sepium (r2 = 0.99; MSE = 15.3), H. brasiletto (r2 = 0.95; MSE = 19.6) and M. frutescens (r2 = 0.98; MSE = 18.1). The regression equations showed the close relationship between stem diameter (dn2 ), stem length (h) and number of stems above ground level. The low mortality shown by the majority of the introduced species coupled with their high reproductive capacities suggests that these species may serve to enrich the matorral of the region, especially for silvicultural purposes. # 2006 Elsevier B.V. All rights reserved. Keywords: Survival; Establishment; Growth; Biomass; Thornscrub; Matorral; Mexico
1. Introduction The selection of introduced tree species for nonindustrial use in developing countries has become an important issue due to the recent world awareness of the importance of forestry to rural development and the pressure to achieve useful results
* Corresponding author. Tel.: +52 81 8114 3465; fax: +52 81 1238 6249. E-mail addresses: [email protected], [email protected] (R. Foroughbakhch). 0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.08.012
quickly (Burley, 1978; Burley and Von Carlowitz, 1984). Unfortunately, there is often a lack of experienced forestry staff for the work involved. Reliable information on ecological, silvicultural and utilization characteristics of many potentially valuable species is still unavailable and hampers species selection (Booth, 1985). The vegetation of most of the inland territories of the coastal plains in the Gulf of Mexico consists of small trees and shrubs, referred locally as ‘‘spiny and subinerm matorral’’ (Ludwig et al., 1975; Rzedowski, 1978; Foroughbakhch et al., 2001). This matorral is composed of almost 60 woody species and many of
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them are important in forestry and for silvipastoral production (timber, posts, firewood, forage, etc.) which constitutes the most common land use. However, the vegetation of this area has been lately undergoing remarked changes in structure, composition and a slow and perhaps irreversible degradation as a result of diverse human activities, such as the selective cutting of certain species or the overgrazing by cattle. The total clearance of the vegetation by heavy machinery and burning for agriculture, orchards or pasture has also been increased lately. The remaining undisturbed areas are threatened by expanded agricultural, horticultural and pasture operations. The loss of vegetation is aggravated when soils are not suitable for farming or pasture, especially in the most arid areas and in sloping terrains (Eviner, 2003; Fahring, 2003). This situation has resulted lately in the gradual decrease of the matorral productivity and has led to an unfavorable economic situation in the affected farming communities. In order to alleviate these unfavorable conditions and as a measure to preserve the ecology of the matorral area a few reforestation programs have been achieved which include reforestation of disturbed areas with native trees. However, although native trees are well adapted to the arid zones, usually their growth rate is slow so reforestation is difficult to achieve with those species or productivity is not high enough to satisfy the requirements of the human populations that use them as their economic livelihood. For these reasons planting introduced tree species with fast growth in their lands of origin is often advised. In order to obtain information about the adaptability, growth, establishment and biomass productivity of exotic species to the soils and climate of the northeastern region of Mexico an experiment with 10 introduced tree species from forest regions of southern Mexico and Central America was carried out in a typical area of the matorral near the ‘‘Sierra Madre Oriental’’ mountains (Table 1). The species were chosen due to their forage production potential and their incorporation in the sustainable management of the remnant matorral (Reid et al., 1990; Navar et al., 1999). The results presented in this paper were obtained during a period of 15 years from planting and represent the survival, growth, establishment and biomass production of the species in northeastern Mexico.
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2. Materials and methods
peak in late spring-early summer (March–June) and the second peak in the late summer-early fall (September–October). The month with the largest mean rainfall is September (180–200 mm) and the lowest monthly registration occurs in December and January (15–20 mm). Average number of rain days per year is 85 with a standard deviation of 15. Approximately, 50% of these rain days have even shown amounts of <5 mm and are related to thunderstorms resulting from deep convection by mid-latitude disturbances (Navar et al., 1999). Cold-front systems generate most of the winter rainfall, accounting for <10% of the long-term annual average. Potential evapotranspiration (PET), estimated by employing the Thornthwait method, is 1150 mm (Navar and Bryan, 1994). The mean annual temperature is 22.3 8C. Daytime temperatures of 45 8C are common during the summer months, and frosts occur in most winter seasons. The highest mean monthly temperature occurs in August (28–29 8C) and the lowest in January (14–15 8C) (SPP, 1981; Cavazos and Molina, 1992). A marked water deficit is evident in July and August, when evaporation exceeds precipitation by almost two and half times. The soils of the study area are typical vertisols (FAOUNESCO, 1974) of alluvial–coluvial origin, deep, and high in clay content, dark in color and relatively low in organic matter. The pH is moderately alkaline and there are severe deficiencies in macronutrients, especially phosphorus (P) and nitrogen (N). Nitrogen is very volatile in the prevailing climate and it is apparently lost when the vegetation is cleared by heavy machinery from sites with diverse species of woody legumes, leaving the soil exposed to alternating conditions of heavy rain and extreme insolation. The moderate alkalinity of this vertisol is due to the high content of CaCO3. The extremely high level of Ca++ which dominates the cation spectrum may impede K+ and Mg++ uptake by plant roots. According to Heiseke and Foroughbakhch (1990), vegetation associated to the study area may be described as dense (2.0–6.4 shrubs m2), shrubby (average height of 1.95–2.63 m) and diverse. Most plant species overlap vertically from 0.5 to 5.0 m (Manzano, 1997; DeSoyza et al., 1997) and horizontally average distance between shrubby stems is 30 cm while mean crown radius is 47 cm, resulting in a mean overlapping radius of 17 cm. Average open space between shrub canopies is 10 cm.
2.1. Description of the study site
2.2. Species selection
This study was conducted within the Matorral School of the Faculty of Forest Science of the Autonomous University of Nuevo Leon. The Matorral School has an area of 300 ha and is located within the lowlands of the northeastern plains of the Gulf of Mexico, 8 km south of Linares city in the State of Nuevo Leon, Mexico (248470 North latitude, 998320 West longitude). The regional climate in the scheme of Ko¨ppen modified by Garcı´a (2004) is defined as semiarid and subhumid. Mean annual rainfall is 810.6 mm (Cavazos and Molina, 1992). Precipitation distribution in the region is bi-modal with the first
The selection of the species was made in accordance to the characteristics of the wood and their potential use by the local population as timber for construction and fuelwood. Furthermore, general utility species combine adequate shape with structural strength and durability. Those harvested trees for high-quality craftsmanship are selected for their combination of beauty, working properties and stability. Thus, 10 exotic species introduced in northeastern Mexico were considered. Table 1 shows information about the wood characteristics and environment requirements of each of these species. In accordance with this table, A. caribaea, Caesalpinia spp., M.
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Table 1 Wood characteristics, environment requirements and uses of 10 woody species introduced in northeastern Mexico Geographic origin
Wood characteristics
Temperature (8C)
Altitude (m)
Rainfall (mm)
Soil needs
Uses
Albizia caribaea
Guatemala–Honduras
22–29
800–1500
500–2000
Guatemala
20–30
500–1200
500–1800
Well-drained, deep with high O.M. Well-drained, deep with high fertility
T, sh, B, Fd, SC, GM
Albizia guachapele
Caesalpinia eriostachys
Mexico (Campeche)
22–32
400–1500
>400
Mexico (laVeracruz) Southern Mexico
20–34 18–29
To 1200
300–1000 400–900
Enterolobium cyclocarpum
Mexico (Veracruz, Tabasco)
17–28
400–1300
500–800
Adaptable to poor soil, no saline tolerant, not water-logged soil Adaptable to dry alkaline soil. Well-drained, deep with medium fertility. Adaptable to a large range of soils.
SC, Fd, Or, H
Caesalpinia velutina Crescentia alata
Gliricidia sepium
Mexico (Veracruz, Chiapas, Campeche)
22–30
500–1600
1200–1800
Adaptable to both moist and dry soil
T, sh, H, Fd, B, GM, Or
Haematoxylon brasiletto
Mexico (Campeche)
15–25
Lowland
>400
Adaptable, calcareous soil, no saline tolerant
T, sh, Fd, Or
Myrospermum frutescens Pithecellobium dulce
Guatemala Southern Mexico
S: whitish, H: light yellowish brown to light brown; moderately hard S: whitish, H: light yellowish to brown and streaked; medium luster, odorless, medium to coarse texture, deeply interlocked grain, decorative, difficult to work, finishes well S: yellowed, H: dark brown; medium luster, no odor, medium to coarse texture, straight to irregular grain S: yellowed or pinkish-white, H: light brown S: pinkish to reddish brown, H: light brown; hard S: whitish, H: reddish-brown; pungent dust, coarse texture, interlocked, ribbon grain, good luster S: light brown, H: dark to reddish brawn; hard and strong, coarse texture, irregular grain, not easily worked, takes a good polish S: whitish to straw-colored, H: bright orange-red; medium to fin texture, odor of violets, irregular grain, brittle, strong and hard, takes a fine polish Hard, heavy S: yellowish, H: yellowish or reddish brown; moderately soft, strong, brittle, take a high polish, not easily worked
To 35 To 34
Lowland To 1800
500–1500 450–600
Very adaptable Very adaptable
T, Fd, Or, SC, Sh. T, sh, SB, F, Fd, Ta, H, Or, B
T, sh, B, Fd
SC, Fd, LF, GM, Sh, Fd, GM, Sh, SC, Or. T, Fd, Or, SC, Sh,
S: sapwood color; H: heartwood color; LF: frost tolerant; B: bee forrage; F: food; Fd: fodder; GM: green manure; H: hedges; Or: ornamentals: SB: shelterbelts; SC: soil conservation; Sh: shade; T: timber; Ta: tannin.
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Species
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frutescens and P. dulce are species whose wood has more strength when compared to C. alata and E. cyclocarpum (no durable wood). The rest of the species (A. guachapele, G. sepium and H. brasiletto) have moderately durable wood. 2.3. Source of seeds and germination treatments Seeds from the chosen species were collected from their regions of origin (Table 1). Once transferred to the matorral zone the seed dormancy was broken and their germination capacity measured as a means to determine the most suitable propagation technique. Three treatments were applied to induce seed germination (Janzen, 1982; Flores and Mora, 1984): (1) Scarification with sandpaper: seeds were ground for 15 min on sandpaper in a wooden box, using a sandpaper-covered block. Most of the testa was thereby removed. (2) Rasping with a file: each seed was filed so as to expose a part of the embryo of the seed, taking care not to damage it. (3) Immersion in hot water (80 8C): seeds were immersed in hot water at 80 8C for 5 min and then kept in water at room temperature for further 24 h. For each treatment we had selected 200 seeds per species, with 25 in one petri dish, applying a randomized complete block with 8 replications for each species and treatment according to The International Seed Testing Association rules (Bekendam and Grob, 1979). Germination tests were conducted in a CLELAND germination cabinet, model 1000 FAATR at a constant temperature (27 2 8C), humidity and light over 30 days. 2.4. Plantation, experiment design and increment measurements Seedlings were obtained in the lab according to the most efficient method obtained for dormancy breaking and transferred to plastic bags (1/2 L), filled with a mixture of equal parts of sand, vertisol and litosol from the region. Six months later, when the young plants reached a height of 30 cm they were planted in 14 m 14 m plots with a spacing of 2 m between and within rows for a total of 49 plants per species (2500 plants ha1) under randomized complete blocks with four repetitions per species (Underwood, 2004). Survival, height and diameter growth, and projection of the crown were recorded each September during 1986–1990 and 1995–2000. To express the tree biomass (oven-dry kilograms) of 10 selected hardwood species, a series of models (allometric equation and multiple linear models) were tested for each component and for total tree. The biomass measures were undertaken in October 2000 on 5 plants per species selected randomly with 4 repetitions (total 20 plants/species), measuring the following parameters—sd: stump diameter at 0.10 m above ground level, d: stem diameter at 0.30 m above ground level, D: stem diameter at 1.30 m above ground level, h: length of the
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main stem and n: number of stems at 0.30 m above ground level as independent variables, according to Maxwell (1985) and Stewart et al. (1992). In the case of multiple stems P (as in our experiment), the squared sum of the stem diameters ( dn2 ) was the parameter that was selected to predict tree biomass. The selection of those variables to be included in the different models was done using a stepwise regression analysis. The growth parameters of the individuals were used to obtain the regression equation which best fitted the relationship between tree biomass and the independent variable to predict the weight of the aboveground portion of the tree. In order to select the best function for each component, we established a ranking based on the r2 (coefficient of determination) and mean square error (MSE), with an error of less than 5% (Crow and Laidly, 1980; Schlaegel, 1982). 2.5. Data calculation The growth parameters and biomass measurements were converted to amounts per year. The mean values and standard errors were calculated for each species. Analysis of variance (ANOVA) was carried out to determine significant differences between the estimated growth parameters of the species. Contrast tests were applied to compare the mean values (Hinkelmann and Kempthorne, 1994). ANOVA and contrast tests were calculated with the statistical package SPSS (v. 11.0). Least significant difference was calculated at 5% probability level (L.S.D. 0.05) according to Zar (1996). 3. Results and discussion 3.1. Germination treatments Mechanical scarification using abrasive tools increased the germination percentage relative to immersion in hot water and the controls (Table 2). For the species Caesalpinia eriostachys (86%), Albizia guachapele (84%) and Pithecellobium dulce (88%), the percentage of germination was higher than that reported by the Oxford Forestry Institute (74, 76 and 85%, respectively). Surprisingly, the controls of all species had a higher germination percentage than seeds immersed in to hot water at 80 8C with subsequent hydration over 24 h. Heat tolerance of seeds of various species has been determined under laboratory conditions. More than 40% of embryos of Albizia caribaea, Crescentia alata, Enterolobium cyclocarpum and Myrospermum frutescens were killed by the high water temperature. The seeds of the species A. caribaea, A. guachapele, Caesalpinia velutina, C. eriostachys and E. cyclocarpum demonstrated physical dormancy, whereas Gliricidia sepium and P. dulce showed no dormancy. Seeds of the two latter species mature at the end of the dry season in the subtropical region of Mexico (Baniwal and Singh, 1989; Zodape, 1991). The physical dormancy of Caesalpinia species has been broken by hot water (Zodape, 1991; Teketay, 1996). However, in our study the best treatment was the scrapping with a file and scarification with sand paper. Similar results were obtained for E. cyclocarpum, in
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Table 2 Species under study and percentage of germination and its standard deviations after treatments Species
Treatments
Albizia caribaea Britton & Rose Albizia guachapele (H.B. & K.) Dugand Caesalpinia eriostachys Benth. Caesalpinia velutina (Britton & Rose) Standl. Crescentia alata H.B. & K. Enterolobium cyclocarpum Griseb. Gliricidia sepium (Jacq.) Steud. Haematoxylon brasiletto Karst. Myrospermum frutescens Jacq. Pithecellobium dulce (Roxb.) Benth.
Control
Scarification sandpaper
Scraping with file
Hot water
78 6.2bc 90 2.8a 90 1.5a 88 2.9a 72 5.6c 83 0.7b 88 2.1a 83 0.9b 63 7.4d 92 1.1a
80 3.0c 93 1.2a 93 0.8a 94 1.3a 76 10.3c 85 3.7b 93 0.5a 89 2.5b 65 8.3d 96 0.9a
50 1.8d 75 2.4b 80 3.1a 78 3.0ab 52 5.6d 62 4.8c 76 2.0b 73 1.6b 38 5.5f 82 0.9a
59 4.8e 79 7.1b 82 1.6a 86 2.3a 61 6.6d 72 5.2bc 81 2.0a 70 8.3bc 40 11.0e 83 4.1a
Different letters (a–f) in columns indicate significant differences (P < 0.05).
contrast with Hunter (1989), who reported that physical methods were not so efficient in breaking physical dormancy in this species. 3.2. Survival and adaptation The great variety of species occurring in northeastern region of Mexico can be categorized in several groups based on their ecological adaptation and use. Many of these species have declined while others are threatened. This situation resulted from the unsustainable use of these tree resources. In our experiment most of exotic species have shown the capacity to survive in places where annual rainfall is 700 mm or less or where rainfall is extremely variable. Thus, P. dulce (98%) and C. eriostachys (96%) had the highest survival rates, followed by G. sepium (95%), H. brasilletto (87%) and A. guachapele (80%) which showed a similar level of adaptability despite plants continuing to die over the 4 following years (Table 3). Their adaptive mechanisms include deep root systems that penetrate to subsoil moisture and provide tolerance to the drought conditions of the semiarid areas of northeastern Mexico. On the other hand, E. cyclocarpum (64%), C. velutina (58%) and C. alata (68%), showed stable survivorship curves but suffered a higher initial mortality than the aforementioned species. The remaining species like A. caribaea and M.
frutescens showed continuing and more substantial losses over the experimental period, indicating their unsuitability for the area. The climatic factors, specially the low temperatures (frost), played an important role in the mortality rate of A. caribaea, M. frutescens and C. velutina since these species were more sensitive to the low temperatures occurred in winter and early spring. Other exotic and naturalized species such as Eucalyptus spp. and Leucaena leucocephala Lam. de Wit have already replaced some local species like Pithecellobium spp., Prosopis spp. and Helietta parvifolia (Gray ex Hemsl.) Benth. (DJogo, 1999; Foroughbakhch et al., 2001) and today they play important roles in the daily life of rural communities or in protecting the environment. Species such as E. cyclocarpum, G. sepium and P. dulce might also be useful in the same way. 3.3. Establishment, height and diameter increment Along with survival, a further criterion to evaluate the development of introduced species for forestry programs is height and diameter increment. These parameters are good indicators of the site conditions (soil and climate) although they are also dependent on factors such as interspecific competition, standard density (spacing) and climatic conditions. This last
Table 3 Survival percentage (mean standard deviation), and contrast information for woody species planted in northeastern Me´xico (n = 200) Species
Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
Year 1985
1986
1990
1995
2000
100 100 100 100 100 100 100 100 100 100
58 9.0d 84 6.6b 99 0.7a 71 3.9c 78 8.5bc 73 7.1c 98 0.5a 97 1.9a 62 8.5d 99 0.8a
49 8.1f 82 2.1c 97 0.6a 65 4.3e 74 3.6d 70 3.5d 96 2.0a 90 4.3b 53 10.3f 98 0.0a
43 7.2f 80 1.7bc 96 0.2a 61 2.3de 70 5.9d 67 9.4d 95 1.8a 88 4.1b 50 9.1e 98 0.0a
38 2.9e 80 0.0b 96 0.0a 58 4.7cd 68 2.7c 64 6.3c 95 0.0a 87 0.8b 47 6.3e 98 0.0a
Different letters (a–f) in columns indicate significant differences (P < 0.05).
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Table 4 Cumulative height increment (mean in meters standard deviation) of 10 introduced species in northeastern Mexico Species
1985
1986
1988
1990
1995
2000
Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
0.35 0.41 0.49 0.24 0.62 0.82 0.65 0.74 0.62 0.85
0.42 0.7 0.84 0.6 1.35 0.4 0.72 0.3 1.55 1.0 1.72 0.6 1.96 0.8 1.59 0.1 1.55 0.4 1.40 0.8
0.82 0.1 1.43 0.4 1.98 0.6 1.05 0.4 2.45 1.2 2.50 0.7 2 96 0.9 1.95 0.3 1.73 0.3 1.96 1.0
1.36 0.6d 1.90 0.4c 2.46 0.6b 1.94 0.7c 3.02 1.4a 2.86 0.3b 3.78 0.4a 2.40 0.3b 1.96 0.6c 2.38 0.2b
2.46 0.2cd 2.65 0.1c 3.41 0.4b 2.48 0.1cd 3.73 0.8b 4.08 0.5a 4.70 0.4a 3.28 0.8b 2.86 0.9c 3.19 0.3bc
2.90 0.1d 3.12 0.4d 3.92 0.7c 2.85 1.2d 4.30 0.9b 4.79 1.5b 5.36 0.9a 4.03 0.6b 3.51 1.9c 3.95 1.0b
Different letters (a–d) in columns indicate significant differences (P < 0.05).
factor seems to determine the growth and development of the species tested in northeastern Mexico. G. sepium, C. alata and E. cyclocarpum showed the fastest growth rate (Table 4) with an average of 35.7, 28.6 and 31.9 cm year1, respectively, with a particularly good drought resistance, even though they were more sensitive to low temperatures during winter and at the beginning of the growing season. The capacity for ready establishment confers to these species aggressive characteristics favoring the invasion of experimental plots in northeastern Mexico. H. brasiletto, M. frutescens and C. velutina showed good growth potential, although less than shown by G. sepium and P. dulce. Their height and basal diameters (Fig. 1) increased constantly across each growing season. On the contrary, A. caribaea and A. guachapele showed the lowest average growth rate, 19.3 and 20.8 cm year1,
respectively, for a period of 10 and 15 years. The rest of the species showed an intermediate growth rate between these two groups. Since most of the species employed in this study develop a broad dispersed canopy, the stand density varied among species as the trees matured. The high initial plant density (2500 plants ha1) and the plantation space available (4 m2) per plant notably influenced the growth in height as well as in diameter of all species. The 10 species showed variable height and diameter increments during 15 years of development (see Fig. 1). G. sepium (1.84 cm year1), P. dulce (1.53 cm year1), E. cyclocarpum (1.48 cm year1), C. alata (1.44 cm year1) and M. frutescens (1.27 cm year1) showed prodigious growth in height and diameter right from the plantation establishment. The data show that the increments in basal diameter from 1985 to 1990 were 20.0% for C. eriostachys y C. velutina, 23%
Fig. 1. Basal diameter increment for 10 introduced woody species in matorral of northeastern Mexico in a period of 15 years.
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for G. sepium, 35% for C. alata and 41% for H. brasiletto. For the period 1990–2000 the increment rank was 56% for M. frutescens, 71% for G. sepium and 76% for C. eriostachys and P. dulce. The growth pattern of all species was affected by the low rainfall (in spring and summer) and high temperatures during the establishment phase (1985–1990). Besides, there were winter frosts (8 8C in Winter 1985 and 3 8C in early spring 1989) which influenced negatively in their growth. After the frosts, all these species reproduced from the remaining stumps. The no significant difference (P > 0.05) between blocks suggests that soil conditions across the experimental area are homogeneous, reflecting the actual situation in the matorral. 3.4. Estimation of tree biomass Under given environmental conditions, biomass production is a function of the crown size since the lateral branches grow more quickly than the central apex (Niembro-Rocas, 1990). The variables measured for the estimation of the tree biomass are shown in Table 5. On the basis of biomass and volume table, and in contrast to most of the biomass studies for many other sub-tropical species, the linear models gave a better estimate of tree biomass than the logarithmic functions. The regression equations for the estimation of tree biomass (Table 6) reveals that the species with the highest coefficient of determination (r2) and lowest mean squared error (MSE), were E. cyclocarpum (r2 = 0.96; MSE = 17.8), G. sepium (r2 = 0.99; MSE = 15.3), H. brasilleto (r2 = 0.95; MSE = 19.6), M. frutescens (r2 = 0.98; MSE = 18.1) y P. dulce (r2 = 0.92; MSE = 32.5). The regression equations for these species showed the close relationship between stem diameter, stem length and number of stems above the ground level. The G. sepium, E. cyclocarpum and M. frutescens quickly produced a broad crown, which in turn gave rise to a large stem diameter. These results were produced from a limited number of observations. In the future, a larger sample should be taken since the values obtained for MSE and SE were high (over 20%) for Albizia spp.; Caesalpinia spp., C. alata and P. dulce. The best estimation was obtained for stem diameter and stem length of the main stem, whereas stump diameter at 10 cm above ground level gave the poorest estimation. Table 5 Average values of main stem length (h), and stump diameter at 0.1 m (sd), 0.30 m (d) and 1.3 m (D) above ground level Species
h (m)
sd (cm)
d (cm)
D (cm)
Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
2.90 3.12 3.92 2.85 4.3 4.79 5.36 4.03 3.51 3.95
12.2 14.9 18.3 21.5 21.6 22.2 27.6 20.8 19.1 22.9
10.4 12.7 17.6 18.1 19.9 20.6 25.5 19.0 17.2 21.8
6.1 7.3 11.5 11.9 13.6 12.4 16.6 15.9 13.9 14.8
Table 6 Regression equations for the estimation of tree biomass (oven-dry kilograms), of selected hardwood species Species Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
Biomass and volume equation P 0:054 sd2n 0:121 P 2 0:143 dn 2:0315h P 0:085h dn2 P 2 0:136 sdn 0:015 P 0:0327h dn2 P 0:0207h dn2 P 2 0:1185 dn P 0:1124 dn2 0.624D 2 P 0:312 dn2
R2
MSE (%)
SE (%)
0.70 0.79 0.81 0.72 0.94 0.96 0.99 0.95 0.98 0.92
39.5 33.6 38.0 36.7 21.1 17.8 15.3 19.6 18.1 32.5
43.5 34.8 36.9 38.1 23.6 20.3 16.7 22.5 19.9 37.4
This is equivalent to the weight of the aboveground portion of the tree (leaves, twigs and wood). Sd: stump diameter at 10 above ground level (cm), d: stem diameter at 0.30 m above ground level (cm), D: stem diameter at 1.30 m above ground level (cm), h: stem length of main stems (m), n: number of stems at 0.30 m above ground level. MSE: mean squared error; SE: standard error.
Data suggest that these species are more capable to establish in cleared sites within the components of the tamaulipan thornscrub. On the basis of these results, it is important to consider these species in agroforestry combinations with crops for management of the matorral. E. cyclocarpum, G. sepium and M. frutescens are the species with the best integrated multipurpose characteristics, with rapid growth and production of leaf/twigs. In accord to Williams (1982), additivity of tree biomass equations is an important factor to consider. To meet this condition a simple model was selected and used for all components. The variables (dn2 ) and (h) were selected because they were included in the stepwise regression analysis in almost equations obtained. The stand density and the biomass of the trees indicate that high biomass was associated with comparatively low stand density. 4. Conclusions The greatest need for the tamaulipan thornscrub is the rehabilitation of marginal lands that have been degraded, compacted and are presently being eroded by inadequate silvipastoral activities. On less productive soils, forestry with a pastoral component should be developed, especially in the matorral, which is under severe pressure due to wood exploitation and overgrazing. In this sense, more than 15 years experience in growing 10 introduced species for plantation in semiarid zones of northeastern Mexico showed that most of these species were well suited to the edaphic and climatic conditions of the region. On vertisols in northeastern Mexico, the exotic species have better and wider ranges of ecological adaptation receiving 700 mm (or less) annual rainfall at elevations of 450 m. The growth rates of G. sepium, E. cyclocarpum, P. dulce and H. brasiletto were clearly superior to the other species under the conditions imposed in this study. These species are exploited
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for multiple purposes in subtropical and tropical zones at southeastern Mexico, which should be considered for future planting in forestry and agroforestry systems. However, A. caribaea and A. guachapele showed limited growth in plantation because they were more sensitive to the drought and low temperatures. Finally, it can be assured that the general methodology applied in this research gave satisfactory results and could be used to develop biomass functions for native species. The tree biomass prediction appears satisfactory over the range of values of diameter and heights. Acknowledgements The Mexican National Science and Technology Council CONACyT–SEMARNAT, and PAICyT funded this research through grants 220/2004-01 and 1096-05, respectively, our gratitude for their economic support. References Baniwal, B.S., Singh, N.B., 1989. Observations on flowering, fruiting and germination behaviours of some useful forest plants of Arunachal pradesh. Indian For. 115, 216–227. Booth, T.H., 1985. A new method for assisting species selection. Commonwealth For. Rev. 64, 241–250. Burley, J., 1978. Selection of species for fuelwood plantations. In: Paper presented, eighth World Forestry Congress, Jakarta. Burley, J., Von Carlowitz, P., 1984. Multipurpose Tree Germplasm. ICRAF, Nairobi. Bekendam, J., Grob, R., 1979. Handbook for Seedling Evaluation, second ed. The International Seed Testing Association (ISTA), Zurich, Switzerland, 130 p. Cavazos, M.T., Molina, V., 1992. Registros climatolo´gicos de la regio´n citrı´cola de Nuevo Leo´n. Facultad de Ciencias Forestales, Universidad Autonoma de Nuevo Leon. Boletı´n Te´cnico No 1: 1-65. Crow, T.R., Laidly, P.R., 1980. Alternative models for estimating woody plant biomass. Can. J. For. Res. 10, 367–370. DeSoyza, A.G., Whitford, W.G., Martinez Meza, E., Van Zee, J.W., 1997. Variation in creosotebush (Larrea tridentate) canopy morphology in relation to habitat, soil fertility and associated annual plant communities. Am. Midl. Nat. 137, 13–26. DJogo, A.P.Y., 1999. Domestication of indigenous and naturalized species for reforestation and agroforestry. In: Roshetko, J. M., Evans, D. O. (Eds.). Domestication of Agroforestry Tree in Southeast Asia. Forest, Farm, and Community Tree Res. Reports (Special Issue). Eviner, V.T., 2003. Functional matrix: a conceptual framework for predicting multiple plant effects on ecosystem processes. Annu. Rev. Ecol. Evol. Syst. 34, 455–485. Fahring, L., 2003. Effects of the habitat fragmentation on biodiversity. Annu. Rev. Ecol. Evol. Syst. 34, 487–515. FAO-UNESCO, 1974. FAO-UNESCO Soil Map of the World, vol. I. UNESCO, Paris. Flores, E.M., Mora, B., 1984. Germination and seedling growth of Pithecellobium arboretum urban. Turrialba 34, 485–488.
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Foroughbakhch, R., Hauad, L.A., Ce´spedes, A.E., Ponce, E.E., Gonza´lez, N., 2001. Evaluation of 15 indigenous and introduced species for reforestation and agroforestry in northeastern Mexico. Agroforestry Syst. 51, 213–221. Garcı´a, E., 2004. Modificaciones al sistema de clasificacio´n clima´tica de Ko¨ppen, Quinta edicio´n. Instituto de Geografı´a, Universidad Nacional Auto´noma de Me´xico, 90 p. Heiseke, D., Foroughbakhch, R., 1990. El matorral como recurso forestal. Reporte cientı´fico numero 1, vol. 1. Facultad de Ciencias Forestales UANL, Linares, Nuevo Leo´n Me´xico, pp. 1–32. Hinkelmann, K., Kempthorne, O., 1994. Design and analysis of experiments. Introduction to Experimental Design, vol. 1. John Wiley & Sons, New York, USA. Hunter, J.R., 1989. Seed dispersal and germination of Enterolobium cyclocapum (Jacq.) Griseb. (Leguminosae: Mimosoideae). J. Biogeogr. 16, 369– 378. Janzen, D.H., 1982. Variation in average seed size and fruit seediness in a fruit crop of Guanacaste tree (Leguminosae: Enterolobium cyclocarpum). Am. J. Bot. 69, 1169–1178. Ludwig, J.A., Reynold, J.F., Whitson, P.D., 1975. Size biomass relationships of several Chihuahuan desert shrubs. Am. Midl. Nat. 94 (2), 451–461. Manzano, M.G., 1997. Procesos de desertificacio´n asociados a sobrepastoreo por caprinos en el matorral espinoso de Linares, Nuevo Leo´n. Tesis de maestrı´a en ciencias. Facultad de Ciencias Forestales. UANL, Me´xico. Maxwell, D.C., 1985. Biomass moisture contents and energy equivalents of tree species in the subtropical dry forest of the Dominican Republic. M.S. Thesis. Ohio State University, Columbus. Navar, J., Bryan, R.B., 1994. Fitting the analytical model of rainfall interception of gash to individual shrubs of semi-arid vegetation in northeastern Mexico. Agric. For. Meterol. 68, 133–143. Navar, J., Charles, F., Jurado, E., 1999. Spatial variations of interception loss components by Tamaulipan thornscrub in northeastern Me´xico. For. Ecol. Manage. 124, 231–239. ´ rboles y arbustos u´tiles de Me´xico. Limusa, Niembro-Rocas, A., 1990. A Me´xico, DF. Reid, N., Stafford Smith, D.M., Beyer-Munzel, P., Marroquin, J., 1990. Floristic and structural variation in the Tamaulipan thornscrub, northeastern Mexico. J. Vegetation Sci. 1, 529–538. Rzedowski, J., 1978. Vegetacio´n de Me´xico, first ed. LIMUSA, Me´xico, DF. Schlaegel, B.E., 1982. Boxelder (Acer negundo L.) biomass component regression analysis for the Mississippi Delta. For. Sci. 28, 355–358. SPP (Secretaria de Programacio´n y Presupuesto), 1981. Carta de climas: escala ¨ PPEN modificado 1: 1,000,000. Hoja Monterrey. Tipos de climas segu´n KO por Garcı´a. Stewart, J.L., Dnudson, A.J., Hellin, J.J, Hughes, C.E., 1992. Wood biomass estimatin of Central American dry zone species. Tropical Forestry Paper 26. Oxford Forestry Institute, Oxford, UK. Teketay, D., 1996. Germination ecology of twelve indigenous and eight exotic multipurpose leguminous species from Ethiopia. For Ecol. Manage. 80, 209–223. Underwood, A.J., 2004. Experiments in ecology: their logical design and interpretation using analysis of variance. Cambridge University Press, 504 p. Williams Jr., J.G., 1982. Modeling problems in predicting total – tree and tree – component biomass. In: Baldwin, Jr., V.C., Lohrey, R.E. (Eds.), Proceedings of the 1982 Southern Forest Biomass Working Group Workshop, Alexandria, LA, USA, pp. 111–115. Zar, J.H., 1996. Biostatistical Analysis, third ed. Prentice-Hall Inc., NJ, USA. Zodape, S.T., 1991. The improvement of germination of some forest species by acid scarification. Indian For. 117, 61–65.
Establishment, growth and biomass production of 10 tree woody species introduced for reforestation and ecological restoration in northeastern Mexico R. Foroughbakhch *, M.A. Alvarado-Va´zquez, J.L. Herna´ndez-Pin˜ero, A. Rocha-Estrada, M.A. Guzma´n-Lucio, E.J. Trevin˜o-Garza Departamento de Bota´nica, Facultad de Ciencias Biolo´gicas, Universidad Auto´noma de Nuevo Leo´n, Box 2-F, Cd. Universitaria, San Nicola´s de los Garza, NL 66451, Mexico Received 15 February 2006; received in revised form 10 August 2006; accepted 10 August 2006
Abstract The coast of the Gulf of Mexico is characterized as a region with high variation in climatic conditions and rich in drought-tolerant or subhumid species. The species that are potentially useful for reforestation, regreening, agroforestry activities and the production of timber and fuelwood have been overexploited, resulting in a gradual decrease and degradation of their populations. In order to restore the soil and rehabilitate the disturbed areas inhabited by matorral vegetation, we tested the adaptability, development and establishment of 10 introduced tree species. The species were: Albizia caribaea Britton & Rose, Albizia guachapele (H.B. & K.) Dugand, Caesalpinia velutina (Britton & Rose) Standl., Caesalpinia eriostachys Benth., Crescentia alata H.B. & K., Enterolobium cyclocarpum Griseb., Gliricidia sepium (Jacq.) Steud., Haematoxylon brasilleto Karst., Myrospermum frutescens Jacq. and Pithecellobium dulce (Roxb.) Benth. The seeds of each species received different pretreatments. Seedlings were grown in plastic bags and planted out after 6 months by hand in August 1985 in a monoculture in four randomized blocks in a cleared area with deep loamy-clay soil, slightly alkaline. Measurements of different growth parameters and leaf/twig biomass over 15 years were evaluated. The species C. alata, E. cyclocarpum, G. sepium and H. brasilleto tended to have better characteristics in terms of growth annual rate (33–62 cm in height and 1.7–2.6 cm in basal diameter during 1985–1990), while A. caribaea, A. guachapele, C. velutina y C. eriostachys (20–30 cm in height and 1.2–1.7 cm in basal diameter) did not establish well due to susceptibility to frost. M. frutescens and P. dulce had intermediate yields of great interest due to their multipurpose potential. The linear models gave a better estimate of tree biomass than the logarithmic functions. The species with the highest determination coefficient (r2) and the lowest mean square error (MSE), were E. cyclocarpum (r2 = 0.96; MSE = 19.8), G. sepium (r2 = 0.99; MSE = 15.3), H. brasiletto (r2 = 0.95; MSE = 19.6) and M. frutescens (r2 = 0.98; MSE = 18.1). The regression equations showed the close relationship between stem diameter (dn2 ), stem length (h) and number of stems above ground level. The low mortality shown by the majority of the introduced species coupled with their high reproductive capacities suggests that these species may serve to enrich the matorral of the region, especially for silvicultural purposes. # 2006 Elsevier B.V. All rights reserved. Keywords: Survival; Establishment; Growth; Biomass; Thornscrub; Matorral; Mexico
1. Introduction The selection of introduced tree species for nonindustrial use in developing countries has become an important issue due to the recent world awareness of the importance of forestry to rural development and the pressure to achieve useful results
* Corresponding author. Tel.: +52 81 8114 3465; fax: +52 81 1238 6249. E-mail addresses: [email protected], [email protected] (R. Foroughbakhch). 0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.08.012
quickly (Burley, 1978; Burley and Von Carlowitz, 1984). Unfortunately, there is often a lack of experienced forestry staff for the work involved. Reliable information on ecological, silvicultural and utilization characteristics of many potentially valuable species is still unavailable and hampers species selection (Booth, 1985). The vegetation of most of the inland territories of the coastal plains in the Gulf of Mexico consists of small trees and shrubs, referred locally as ‘‘spiny and subinerm matorral’’ (Ludwig et al., 1975; Rzedowski, 1978; Foroughbakhch et al., 2001). This matorral is composed of almost 60 woody species and many of
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them are important in forestry and for silvipastoral production (timber, posts, firewood, forage, etc.) which constitutes the most common land use. However, the vegetation of this area has been lately undergoing remarked changes in structure, composition and a slow and perhaps irreversible degradation as a result of diverse human activities, such as the selective cutting of certain species or the overgrazing by cattle. The total clearance of the vegetation by heavy machinery and burning for agriculture, orchards or pasture has also been increased lately. The remaining undisturbed areas are threatened by expanded agricultural, horticultural and pasture operations. The loss of vegetation is aggravated when soils are not suitable for farming or pasture, especially in the most arid areas and in sloping terrains (Eviner, 2003; Fahring, 2003). This situation has resulted lately in the gradual decrease of the matorral productivity and has led to an unfavorable economic situation in the affected farming communities. In order to alleviate these unfavorable conditions and as a measure to preserve the ecology of the matorral area a few reforestation programs have been achieved which include reforestation of disturbed areas with native trees. However, although native trees are well adapted to the arid zones, usually their growth rate is slow so reforestation is difficult to achieve with those species or productivity is not high enough to satisfy the requirements of the human populations that use them as their economic livelihood. For these reasons planting introduced tree species with fast growth in their lands of origin is often advised. In order to obtain information about the adaptability, growth, establishment and biomass productivity of exotic species to the soils and climate of the northeastern region of Mexico an experiment with 10 introduced tree species from forest regions of southern Mexico and Central America was carried out in a typical area of the matorral near the ‘‘Sierra Madre Oriental’’ mountains (Table 1). The species were chosen due to their forage production potential and their incorporation in the sustainable management of the remnant matorral (Reid et al., 1990; Navar et al., 1999). The results presented in this paper were obtained during a period of 15 years from planting and represent the survival, growth, establishment and biomass production of the species in northeastern Mexico.
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2. Materials and methods
peak in late spring-early summer (March–June) and the second peak in the late summer-early fall (September–October). The month with the largest mean rainfall is September (180–200 mm) and the lowest monthly registration occurs in December and January (15–20 mm). Average number of rain days per year is 85 with a standard deviation of 15. Approximately, 50% of these rain days have even shown amounts of <5 mm and are related to thunderstorms resulting from deep convection by mid-latitude disturbances (Navar et al., 1999). Cold-front systems generate most of the winter rainfall, accounting for <10% of the long-term annual average. Potential evapotranspiration (PET), estimated by employing the Thornthwait method, is 1150 mm (Navar and Bryan, 1994). The mean annual temperature is 22.3 8C. Daytime temperatures of 45 8C are common during the summer months, and frosts occur in most winter seasons. The highest mean monthly temperature occurs in August (28–29 8C) and the lowest in January (14–15 8C) (SPP, 1981; Cavazos and Molina, 1992). A marked water deficit is evident in July and August, when evaporation exceeds precipitation by almost two and half times. The soils of the study area are typical vertisols (FAOUNESCO, 1974) of alluvial–coluvial origin, deep, and high in clay content, dark in color and relatively low in organic matter. The pH is moderately alkaline and there are severe deficiencies in macronutrients, especially phosphorus (P) and nitrogen (N). Nitrogen is very volatile in the prevailing climate and it is apparently lost when the vegetation is cleared by heavy machinery from sites with diverse species of woody legumes, leaving the soil exposed to alternating conditions of heavy rain and extreme insolation. The moderate alkalinity of this vertisol is due to the high content of CaCO3. The extremely high level of Ca++ which dominates the cation spectrum may impede K+ and Mg++ uptake by plant roots. According to Heiseke and Foroughbakhch (1990), vegetation associated to the study area may be described as dense (2.0–6.4 shrubs m2), shrubby (average height of 1.95–2.63 m) and diverse. Most plant species overlap vertically from 0.5 to 5.0 m (Manzano, 1997; DeSoyza et al., 1997) and horizontally average distance between shrubby stems is 30 cm while mean crown radius is 47 cm, resulting in a mean overlapping radius of 17 cm. Average open space between shrub canopies is 10 cm.
2.1. Description of the study site
2.2. Species selection
This study was conducted within the Matorral School of the Faculty of Forest Science of the Autonomous University of Nuevo Leon. The Matorral School has an area of 300 ha and is located within the lowlands of the northeastern plains of the Gulf of Mexico, 8 km south of Linares city in the State of Nuevo Leon, Mexico (248470 North latitude, 998320 West longitude). The regional climate in the scheme of Ko¨ppen modified by Garcı´a (2004) is defined as semiarid and subhumid. Mean annual rainfall is 810.6 mm (Cavazos and Molina, 1992). Precipitation distribution in the region is bi-modal with the first
The selection of the species was made in accordance to the characteristics of the wood and their potential use by the local population as timber for construction and fuelwood. Furthermore, general utility species combine adequate shape with structural strength and durability. Those harvested trees for high-quality craftsmanship are selected for their combination of beauty, working properties and stability. Thus, 10 exotic species introduced in northeastern Mexico were considered. Table 1 shows information about the wood characteristics and environment requirements of each of these species. In accordance with this table, A. caribaea, Caesalpinia spp., M.
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Table 1 Wood characteristics, environment requirements and uses of 10 woody species introduced in northeastern Mexico Geographic origin
Wood characteristics
Temperature (8C)
Altitude (m)
Rainfall (mm)
Soil needs
Uses
Albizia caribaea
Guatemala–Honduras
22–29
800–1500
500–2000
Guatemala
20–30
500–1200
500–1800
Well-drained, deep with high O.M. Well-drained, deep with high fertility
T, sh, B, Fd, SC, GM
Albizia guachapele
Caesalpinia eriostachys
Mexico (Campeche)
22–32
400–1500
>400
Mexico (laVeracruz) Southern Mexico
20–34 18–29
To 1200
300–1000 400–900
Enterolobium cyclocarpum
Mexico (Veracruz, Tabasco)
17–28
400–1300
500–800
Adaptable to poor soil, no saline tolerant, not water-logged soil Adaptable to dry alkaline soil. Well-drained, deep with medium fertility. Adaptable to a large range of soils.
SC, Fd, Or, H
Caesalpinia velutina Crescentia alata
Gliricidia sepium
Mexico (Veracruz, Chiapas, Campeche)
22–30
500–1600
1200–1800
Adaptable to both moist and dry soil
T, sh, H, Fd, B, GM, Or
Haematoxylon brasiletto
Mexico (Campeche)
15–25
Lowland
>400
Adaptable, calcareous soil, no saline tolerant
T, sh, Fd, Or
Myrospermum frutescens Pithecellobium dulce
Guatemala Southern Mexico
S: whitish, H: light yellowish brown to light brown; moderately hard S: whitish, H: light yellowish to brown and streaked; medium luster, odorless, medium to coarse texture, deeply interlocked grain, decorative, difficult to work, finishes well S: yellowed, H: dark brown; medium luster, no odor, medium to coarse texture, straight to irregular grain S: yellowed or pinkish-white, H: light brown S: pinkish to reddish brown, H: light brown; hard S: whitish, H: reddish-brown; pungent dust, coarse texture, interlocked, ribbon grain, good luster S: light brown, H: dark to reddish brawn; hard and strong, coarse texture, irregular grain, not easily worked, takes a good polish S: whitish to straw-colored, H: bright orange-red; medium to fin texture, odor of violets, irregular grain, brittle, strong and hard, takes a fine polish Hard, heavy S: yellowish, H: yellowish or reddish brown; moderately soft, strong, brittle, take a high polish, not easily worked
To 35 To 34
Lowland To 1800
500–1500 450–600
Very adaptable Very adaptable
T, Fd, Or, SC, Sh. T, sh, SB, F, Fd, Ta, H, Or, B
T, sh, B, Fd
SC, Fd, LF, GM, Sh, Fd, GM, Sh, SC, Or. T, Fd, Or, SC, Sh,
S: sapwood color; H: heartwood color; LF: frost tolerant; B: bee forrage; F: food; Fd: fodder; GM: green manure; H: hedges; Or: ornamentals: SB: shelterbelts; SC: soil conservation; Sh: shade; T: timber; Ta: tannin.
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Species
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frutescens and P. dulce are species whose wood has more strength when compared to C. alata and E. cyclocarpum (no durable wood). The rest of the species (A. guachapele, G. sepium and H. brasiletto) have moderately durable wood. 2.3. Source of seeds and germination treatments Seeds from the chosen species were collected from their regions of origin (Table 1). Once transferred to the matorral zone the seed dormancy was broken and their germination capacity measured as a means to determine the most suitable propagation technique. Three treatments were applied to induce seed germination (Janzen, 1982; Flores and Mora, 1984): (1) Scarification with sandpaper: seeds were ground for 15 min on sandpaper in a wooden box, using a sandpaper-covered block. Most of the testa was thereby removed. (2) Rasping with a file: each seed was filed so as to expose a part of the embryo of the seed, taking care not to damage it. (3) Immersion in hot water (80 8C): seeds were immersed in hot water at 80 8C for 5 min and then kept in water at room temperature for further 24 h. For each treatment we had selected 200 seeds per species, with 25 in one petri dish, applying a randomized complete block with 8 replications for each species and treatment according to The International Seed Testing Association rules (Bekendam and Grob, 1979). Germination tests were conducted in a CLELAND germination cabinet, model 1000 FAATR at a constant temperature (27 2 8C), humidity and light over 30 days. 2.4. Plantation, experiment design and increment measurements Seedlings were obtained in the lab according to the most efficient method obtained for dormancy breaking and transferred to plastic bags (1/2 L), filled with a mixture of equal parts of sand, vertisol and litosol from the region. Six months later, when the young plants reached a height of 30 cm they were planted in 14 m 14 m plots with a spacing of 2 m between and within rows for a total of 49 plants per species (2500 plants ha1) under randomized complete blocks with four repetitions per species (Underwood, 2004). Survival, height and diameter growth, and projection of the crown were recorded each September during 1986–1990 and 1995–2000. To express the tree biomass (oven-dry kilograms) of 10 selected hardwood species, a series of models (allometric equation and multiple linear models) were tested for each component and for total tree. The biomass measures were undertaken in October 2000 on 5 plants per species selected randomly with 4 repetitions (total 20 plants/species), measuring the following parameters—sd: stump diameter at 0.10 m above ground level, d: stem diameter at 0.30 m above ground level, D: stem diameter at 1.30 m above ground level, h: length of the
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main stem and n: number of stems at 0.30 m above ground level as independent variables, according to Maxwell (1985) and Stewart et al. (1992). In the case of multiple stems P (as in our experiment), the squared sum of the stem diameters ( dn2 ) was the parameter that was selected to predict tree biomass. The selection of those variables to be included in the different models was done using a stepwise regression analysis. The growth parameters of the individuals were used to obtain the regression equation which best fitted the relationship between tree biomass and the independent variable to predict the weight of the aboveground portion of the tree. In order to select the best function for each component, we established a ranking based on the r2 (coefficient of determination) and mean square error (MSE), with an error of less than 5% (Crow and Laidly, 1980; Schlaegel, 1982). 2.5. Data calculation The growth parameters and biomass measurements were converted to amounts per year. The mean values and standard errors were calculated for each species. Analysis of variance (ANOVA) was carried out to determine significant differences between the estimated growth parameters of the species. Contrast tests were applied to compare the mean values (Hinkelmann and Kempthorne, 1994). ANOVA and contrast tests were calculated with the statistical package SPSS (v. 11.0). Least significant difference was calculated at 5% probability level (L.S.D. 0.05) according to Zar (1996). 3. Results and discussion 3.1. Germination treatments Mechanical scarification using abrasive tools increased the germination percentage relative to immersion in hot water and the controls (Table 2). For the species Caesalpinia eriostachys (86%), Albizia guachapele (84%) and Pithecellobium dulce (88%), the percentage of germination was higher than that reported by the Oxford Forestry Institute (74, 76 and 85%, respectively). Surprisingly, the controls of all species had a higher germination percentage than seeds immersed in to hot water at 80 8C with subsequent hydration over 24 h. Heat tolerance of seeds of various species has been determined under laboratory conditions. More than 40% of embryos of Albizia caribaea, Crescentia alata, Enterolobium cyclocarpum and Myrospermum frutescens were killed by the high water temperature. The seeds of the species A. caribaea, A. guachapele, Caesalpinia velutina, C. eriostachys and E. cyclocarpum demonstrated physical dormancy, whereas Gliricidia sepium and P. dulce showed no dormancy. Seeds of the two latter species mature at the end of the dry season in the subtropical region of Mexico (Baniwal and Singh, 1989; Zodape, 1991). The physical dormancy of Caesalpinia species has been broken by hot water (Zodape, 1991; Teketay, 1996). However, in our study the best treatment was the scrapping with a file and scarification with sand paper. Similar results were obtained for E. cyclocarpum, in
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Table 2 Species under study and percentage of germination and its standard deviations after treatments Species
Treatments
Albizia caribaea Britton & Rose Albizia guachapele (H.B. & K.) Dugand Caesalpinia eriostachys Benth. Caesalpinia velutina (Britton & Rose) Standl. Crescentia alata H.B. & K. Enterolobium cyclocarpum Griseb. Gliricidia sepium (Jacq.) Steud. Haematoxylon brasiletto Karst. Myrospermum frutescens Jacq. Pithecellobium dulce (Roxb.) Benth.
Control
Scarification sandpaper
Scraping with file
Hot water
78 6.2bc 90 2.8a 90 1.5a 88 2.9a 72 5.6c 83 0.7b 88 2.1a 83 0.9b 63 7.4d 92 1.1a
80 3.0c 93 1.2a 93 0.8a 94 1.3a 76 10.3c 85 3.7b 93 0.5a 89 2.5b 65 8.3d 96 0.9a
50 1.8d 75 2.4b 80 3.1a 78 3.0ab 52 5.6d 62 4.8c 76 2.0b 73 1.6b 38 5.5f 82 0.9a
59 4.8e 79 7.1b 82 1.6a 86 2.3a 61 6.6d 72 5.2bc 81 2.0a 70 8.3bc 40 11.0e 83 4.1a
Different letters (a–f) in columns indicate significant differences (P < 0.05).
contrast with Hunter (1989), who reported that physical methods were not so efficient in breaking physical dormancy in this species. 3.2. Survival and adaptation The great variety of species occurring in northeastern region of Mexico can be categorized in several groups based on their ecological adaptation and use. Many of these species have declined while others are threatened. This situation resulted from the unsustainable use of these tree resources. In our experiment most of exotic species have shown the capacity to survive in places where annual rainfall is 700 mm or less or where rainfall is extremely variable. Thus, P. dulce (98%) and C. eriostachys (96%) had the highest survival rates, followed by G. sepium (95%), H. brasilletto (87%) and A. guachapele (80%) which showed a similar level of adaptability despite plants continuing to die over the 4 following years (Table 3). Their adaptive mechanisms include deep root systems that penetrate to subsoil moisture and provide tolerance to the drought conditions of the semiarid areas of northeastern Mexico. On the other hand, E. cyclocarpum (64%), C. velutina (58%) and C. alata (68%), showed stable survivorship curves but suffered a higher initial mortality than the aforementioned species. The remaining species like A. caribaea and M.
frutescens showed continuing and more substantial losses over the experimental period, indicating their unsuitability for the area. The climatic factors, specially the low temperatures (frost), played an important role in the mortality rate of A. caribaea, M. frutescens and C. velutina since these species were more sensitive to the low temperatures occurred in winter and early spring. Other exotic and naturalized species such as Eucalyptus spp. and Leucaena leucocephala Lam. de Wit have already replaced some local species like Pithecellobium spp., Prosopis spp. and Helietta parvifolia (Gray ex Hemsl.) Benth. (DJogo, 1999; Foroughbakhch et al., 2001) and today they play important roles in the daily life of rural communities or in protecting the environment. Species such as E. cyclocarpum, G. sepium and P. dulce might also be useful in the same way. 3.3. Establishment, height and diameter increment Along with survival, a further criterion to evaluate the development of introduced species for forestry programs is height and diameter increment. These parameters are good indicators of the site conditions (soil and climate) although they are also dependent on factors such as interspecific competition, standard density (spacing) and climatic conditions. This last
Table 3 Survival percentage (mean standard deviation), and contrast information for woody species planted in northeastern Me´xico (n = 200) Species
Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
Year 1985
1986
1990
1995
2000
100 100 100 100 100 100 100 100 100 100
58 9.0d 84 6.6b 99 0.7a 71 3.9c 78 8.5bc 73 7.1c 98 0.5a 97 1.9a 62 8.5d 99 0.8a
49 8.1f 82 2.1c 97 0.6a 65 4.3e 74 3.6d 70 3.5d 96 2.0a 90 4.3b 53 10.3f 98 0.0a
43 7.2f 80 1.7bc 96 0.2a 61 2.3de 70 5.9d 67 9.4d 95 1.8a 88 4.1b 50 9.1e 98 0.0a
38 2.9e 80 0.0b 96 0.0a 58 4.7cd 68 2.7c 64 6.3c 95 0.0a 87 0.8b 47 6.3e 98 0.0a
Different letters (a–f) in columns indicate significant differences (P < 0.05).
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199
Table 4 Cumulative height increment (mean in meters standard deviation) of 10 introduced species in northeastern Mexico Species
1985
1986
1988
1990
1995
2000
Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
0.35 0.41 0.49 0.24 0.62 0.82 0.65 0.74 0.62 0.85
0.42 0.7 0.84 0.6 1.35 0.4 0.72 0.3 1.55 1.0 1.72 0.6 1.96 0.8 1.59 0.1 1.55 0.4 1.40 0.8
0.82 0.1 1.43 0.4 1.98 0.6 1.05 0.4 2.45 1.2 2.50 0.7 2 96 0.9 1.95 0.3 1.73 0.3 1.96 1.0
1.36 0.6d 1.90 0.4c 2.46 0.6b 1.94 0.7c 3.02 1.4a 2.86 0.3b 3.78 0.4a 2.40 0.3b 1.96 0.6c 2.38 0.2b
2.46 0.2cd 2.65 0.1c 3.41 0.4b 2.48 0.1cd 3.73 0.8b 4.08 0.5a 4.70 0.4a 3.28 0.8b 2.86 0.9c 3.19 0.3bc
2.90 0.1d 3.12 0.4d 3.92 0.7c 2.85 1.2d 4.30 0.9b 4.79 1.5b 5.36 0.9a 4.03 0.6b 3.51 1.9c 3.95 1.0b
Different letters (a–d) in columns indicate significant differences (P < 0.05).
factor seems to determine the growth and development of the species tested in northeastern Mexico. G. sepium, C. alata and E. cyclocarpum showed the fastest growth rate (Table 4) with an average of 35.7, 28.6 and 31.9 cm year1, respectively, with a particularly good drought resistance, even though they were more sensitive to low temperatures during winter and at the beginning of the growing season. The capacity for ready establishment confers to these species aggressive characteristics favoring the invasion of experimental plots in northeastern Mexico. H. brasiletto, M. frutescens and C. velutina showed good growth potential, although less than shown by G. sepium and P. dulce. Their height and basal diameters (Fig. 1) increased constantly across each growing season. On the contrary, A. caribaea and A. guachapele showed the lowest average growth rate, 19.3 and 20.8 cm year1,
respectively, for a period of 10 and 15 years. The rest of the species showed an intermediate growth rate between these two groups. Since most of the species employed in this study develop a broad dispersed canopy, the stand density varied among species as the trees matured. The high initial plant density (2500 plants ha1) and the plantation space available (4 m2) per plant notably influenced the growth in height as well as in diameter of all species. The 10 species showed variable height and diameter increments during 15 years of development (see Fig. 1). G. sepium (1.84 cm year1), P. dulce (1.53 cm year1), E. cyclocarpum (1.48 cm year1), C. alata (1.44 cm year1) and M. frutescens (1.27 cm year1) showed prodigious growth in height and diameter right from the plantation establishment. The data show that the increments in basal diameter from 1985 to 1990 were 20.0% for C. eriostachys y C. velutina, 23%
Fig. 1. Basal diameter increment for 10 introduced woody species in matorral of northeastern Mexico in a period of 15 years.
200
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for G. sepium, 35% for C. alata and 41% for H. brasiletto. For the period 1990–2000 the increment rank was 56% for M. frutescens, 71% for G. sepium and 76% for C. eriostachys and P. dulce. The growth pattern of all species was affected by the low rainfall (in spring and summer) and high temperatures during the establishment phase (1985–1990). Besides, there were winter frosts (8 8C in Winter 1985 and 3 8C in early spring 1989) which influenced negatively in their growth. After the frosts, all these species reproduced from the remaining stumps. The no significant difference (P > 0.05) between blocks suggests that soil conditions across the experimental area are homogeneous, reflecting the actual situation in the matorral. 3.4. Estimation of tree biomass Under given environmental conditions, biomass production is a function of the crown size since the lateral branches grow more quickly than the central apex (Niembro-Rocas, 1990). The variables measured for the estimation of the tree biomass are shown in Table 5. On the basis of biomass and volume table, and in contrast to most of the biomass studies for many other sub-tropical species, the linear models gave a better estimate of tree biomass than the logarithmic functions. The regression equations for the estimation of tree biomass (Table 6) reveals that the species with the highest coefficient of determination (r2) and lowest mean squared error (MSE), were E. cyclocarpum (r2 = 0.96; MSE = 17.8), G. sepium (r2 = 0.99; MSE = 15.3), H. brasilleto (r2 = 0.95; MSE = 19.6), M. frutescens (r2 = 0.98; MSE = 18.1) y P. dulce (r2 = 0.92; MSE = 32.5). The regression equations for these species showed the close relationship between stem diameter, stem length and number of stems above the ground level. The G. sepium, E. cyclocarpum and M. frutescens quickly produced a broad crown, which in turn gave rise to a large stem diameter. These results were produced from a limited number of observations. In the future, a larger sample should be taken since the values obtained for MSE and SE were high (over 20%) for Albizia spp.; Caesalpinia spp., C. alata and P. dulce. The best estimation was obtained for stem diameter and stem length of the main stem, whereas stump diameter at 10 cm above ground level gave the poorest estimation. Table 5 Average values of main stem length (h), and stump diameter at 0.1 m (sd), 0.30 m (d) and 1.3 m (D) above ground level Species
h (m)
sd (cm)
d (cm)
D (cm)
Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
2.90 3.12 3.92 2.85 4.3 4.79 5.36 4.03 3.51 3.95
12.2 14.9 18.3 21.5 21.6 22.2 27.6 20.8 19.1 22.9
10.4 12.7 17.6 18.1 19.9 20.6 25.5 19.0 17.2 21.8
6.1 7.3 11.5 11.9 13.6 12.4 16.6 15.9 13.9 14.8
Table 6 Regression equations for the estimation of tree biomass (oven-dry kilograms), of selected hardwood species Species Albizia caribaea Albizia guachapele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Haematoxylon brasiletto Myrospermum frutescens Pithecellobium dulce
Biomass and volume equation P 0:054 sd2n 0:121 P 2 0:143 dn 2:0315h P 0:085h dn2 P 2 0:136 sdn 0:015 P 0:0327h dn2 P 0:0207h dn2 P 2 0:1185 dn P 0:1124 dn2 0.624D 2 P 0:312 dn2
R2
MSE (%)
SE (%)
0.70 0.79 0.81 0.72 0.94 0.96 0.99 0.95 0.98 0.92
39.5 33.6 38.0 36.7 21.1 17.8 15.3 19.6 18.1 32.5
43.5 34.8 36.9 38.1 23.6 20.3 16.7 22.5 19.9 37.4
This is equivalent to the weight of the aboveground portion of the tree (leaves, twigs and wood). Sd: stump diameter at 10 above ground level (cm), d: stem diameter at 0.30 m above ground level (cm), D: stem diameter at 1.30 m above ground level (cm), h: stem length of main stems (m), n: number of stems at 0.30 m above ground level. MSE: mean squared error; SE: standard error.
Data suggest that these species are more capable to establish in cleared sites within the components of the tamaulipan thornscrub. On the basis of these results, it is important to consider these species in agroforestry combinations with crops for management of the matorral. E. cyclocarpum, G. sepium and M. frutescens are the species with the best integrated multipurpose characteristics, with rapid growth and production of leaf/twigs. In accord to Williams (1982), additivity of tree biomass equations is an important factor to consider. To meet this condition a simple model was selected and used for all components. The variables (dn2 ) and (h) were selected because they were included in the stepwise regression analysis in almost equations obtained. The stand density and the biomass of the trees indicate that high biomass was associated with comparatively low stand density. 4. Conclusions The greatest need for the tamaulipan thornscrub is the rehabilitation of marginal lands that have been degraded, compacted and are presently being eroded by inadequate silvipastoral activities. On less productive soils, forestry with a pastoral component should be developed, especially in the matorral, which is under severe pressure due to wood exploitation and overgrazing. In this sense, more than 15 years experience in growing 10 introduced species for plantation in semiarid zones of northeastern Mexico showed that most of these species were well suited to the edaphic and climatic conditions of the region. On vertisols in northeastern Mexico, the exotic species have better and wider ranges of ecological adaptation receiving 700 mm (or less) annual rainfall at elevations of 450 m. The growth rates of G. sepium, E. cyclocarpum, P. dulce and H. brasiletto were clearly superior to the other species under the conditions imposed in this study. These species are exploited
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