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Secondary forest regeneration beneath pine (Pinus kesiya) plantations in the northern Thai highlands: a chronosequence study
Forestry Ecology and Management 99 (1997) 171–183
Secondary forest regeneration beneath pine (Pinus kesiya) plantations in the northern Thai highlands: a chronosequence study Ulrich Oberhauser* John-F.-Kennedy-Str. 41, 73037 Goeppingen, Germany Accepted 9 May 1997
Abstract Northern Thailand has witnessed rapid and extensive forest loss over the past 30 years for many reasons. In response to this, the Royal Forest Department has pursued a highland reforestation program which has led to 1500 km2 of established Pinus kesiya plantations. Present forest management objectives, however, favor more natural mixed forests. Research was carried out in a highland area (1400 km2) of Chiang Mai Province in order to answer the following questions. Does planting of P. kesiya on abandoned agricultural areas effect the rate of natural forest succession? How do these plantations change structurally through the years? Four pine plantations, aged 7, 12, 21 and 28 years, similar in stand and site conditions, were selected and also compared to unplanted regenerating fields aged 3, 6 and 12 years. Basal area, distribution of trees, species composition, diversity and seed dispersal mechanisms were examined. Results of the study revealed a high number of vascular species in the 12-, 21- and 28-year-old plots. An increasingly complex forest structure could be observed as mid- and low-level canopies had developed and other species replaced pines in the overstorey. Increasing numbers of animal dispersed tree species became established in the older plantations. Recovery of woody vegetation was faster in plantations than in areas not afforested with P. kesiya. Over time, the basal stem area of pines which had died or had been cut was replaced by the basal area of other tree species. It appears that P. kesiya plantations can enhance establishment of mixed forests. The implications of afforestations with pine, stand management practices, such as density and fire management, wildlife enhancement and possible disturbances, are also discussed. 1997 Elsevier Science B.V. Keywords: Pinus kesiya; Natural regeneration; Plantation; Diversity; Conversion management
1. Introduction During the years from 1961 to 1991, forest cover in Thailand decreased from 53 to 26.7%. This has occurred despite various measures undertaken by the Royal Thai Government, such as banning of logging concessions, establishing protected areas (including National Parks and Wildlife Sanctuaries) and launching reforestation programs. The northern mountains are of major importance to Thailand’s development. * Tel.: +49 7161 68281; fax: +49 7161 927316.
They are the watershed for the four major rivers forming the Chao Phraya river that supplies the Central Plain, Thailand s center of rice production and Bangkok metropolis. The current goal of the Royal Forest Department (RFD) is to achieve 40% forest cover nationwide, of which 28% is to be in protected areas. Most northern watersheds are located in this protected area system. It is estimated that about 320 km2 of forest area is destroyed every year in the north, mainly by forest fires, logging and swidden cultivation. In the 1960s the RFD promoted establishment of Pinus kesiya plantations. Initially on a limited scale,
0378-1127/97/$17.00 1997 Elsevier Science B.V. All rights reserved PII S0378-1127 (97 )0 0203-X
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 1 Characteristics of study plots in P. kesiya plantations and in natural succession plots in abandoned Lisu fields Plot codea
Altitude (masl)
Slope (%)
Aspect
Soil
P. kesiya (no./plot)
Vegetative cover
P7 P12 P21 P28 L3 L6 L12
1290 1330 1320 1250 1200 1200 1200
47 49 43 50 25 35 50
E E N-E E E S-W S
Podzolic Podzolic Podzolic Podzolic Podzolic Podzolic Podzolic
98 45 82 33 0 0 0
Plantation/weed/grass Plantation/forest Plantation/forest Forest Grasses and climbers Weed, shrub Shrub, saplings
a
P, P. kesiya plantation; L, natural succession in abandoned Lisu fields; numbers indicate years after plantation/length of abandonment.
this effort was expanded in the 1970s and carried out by 113 Watershed Development Units. As a result, approximately 1500 km2 of P. kesiya plantations in northern Thailand are now covered with these pine plantations (RFD, 1993). P. kesiya is a three-needled pine native to Thailand. It is one of the most intensively studied tree species in Thailand (Kijkar, 1987; Koskela et al., 1995; Werner, 1996). The provenances used are usually of local origin. This species occurs naturally in two distinct vegetation types, i.e. lower montane pine-oak forest and pine-deciduous dipterocarp forest (Santisuk, 1988). The latter has rarely been converted to agriculture or to pine plantations. Lower montane pine-oak forest may be considered a severely disturbed stage of a lower montane oak forest influenced by biotic (burning, grazing, cutting) or edaphic factors. It is best developed on elevations ranging from 1000–1400 m, though some pines can be found as low as 600 m and as high as 1900 m. The pines in the lower montane pine-oak forest are up to 40 m tall and grow mostly on ridges and on steep slopes. It is the climax type on many afforestation sites. P. kesiya thrives well on red to yellow granitic soil types (Santisuk, 1988). Today, a mixture of species is used in most afforestations. The more common species on higher elevations are Prunus ceraoides, Docynia indica, Betula alnoides and Schima wallichii. However, P. kesiya still makes up some 50% of all trees planted today. This study aimed to evaluate the potential of P. kesiya afforestations as catalysts for natural forest regeneration. The current management goal is to establish diverse, site adapted, multistory and sustainably manageable forests which fulfill watershed functions with little damage to the environment. Can this be achieved
within a reasonable length of time by planting pines on severely disturbed and degraded sites in watershed areas?
2. Materials and methods 2.1. Site description The study site was located in Watershed Development Unit No. 26, Khun Khong, on a mountain ridge between the Taeng and Ping rivers 100 km north of Chiang Mai, in the districts of Chiang Dao and Wiang Haeng, Chiang Mai Province in northern Thailand. Soils were sandy to loamy lateritic podsols. These types of soil cover vast areas of the highlands in the western parts of northern Thailand. The entire area is mountainous with an altitude of 1100–1500 m. Average temperatures range between 10 and 27°C, with occasional frosts. Average annual rainfall is approximately 2000 mm which falls within a 5-month period (Phugjaroon and Kaewamphut, 1993). The study site is in an area formerly cultivated by Lisu people, whose agricultural practices are commonly classified as ‘long cultivation – very long fallow’. In this cultivation system forest is cleared and cultivated for several years before being abandoned due to declining soil fertility, increasing weed pressure and erosion. Grasses and herbs soon cover abandoned fields which regenerate very slowly and are prone to wild fires. In 1965 the Royal Forest Department planted the first pines in areas where the forests were already destroyed in order to produce wood for the developing paper industry. In 1973 the Watershed Management Division took over and continued to grow pines to
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
protect and rehabilitate watersheds. Today Khun Khong has some of the oldest native pine plantations in mainland Southeast Asia. The afforestation activities resulted in 3724 ha of man-made forests in Khun Khong. The annual reforestation area for the 7-, 12-, 21- and 28-year-old plantations were 89, 128, 80 and 80 ha, respectively. Prior to afforestation the study site was subject to three different kinds of disturbances. The first disturbance, grazing, hunting and some burning, led to a lower montane pine-oak forest. The second and most severe disturbance was the clearing of the forest for agriculture which left only a few seed trees and eliminated most coppicing species. The third was frequent and ongoing disturbance by fire, cattle and tree cutting. The initial spacing of the pine trees was 4 × 4 m. There were no major differences in site preparation during the planting program. Native trees were never cut intentionally and fire was not used during site preparation. In the first 3 years after planting, weeding was carried out in a combination of strip and local point weeding. In all activities the workers were instructed to retain native trees. No fires were recorded in the 7- and 12-year-old plots, however, the 21- and 28-year-old sites each had a ground fire (Phugjaroon, pers. commun.). The plots were chosen so as to be as similar as possible concerning soil, aspect, altitude, slope and all other relevant charac-teristics, of which Table 1 gives a short overview.
Fig. 1. Stem basal area of P. kesiya and other tree species in 7-, 12-, 21- and 28-year-old P. kesiya plantations (Bitterlich method) and in 3-, 6- and 12-year-old abandoned Lisu fields (plot data).
173
Fig. 2. Number of P. kesiya and other tree species in 7-, 12-, 21and 28-year-old P. kesiya plantation plots and in 3-, 6- and 12-yearold abandoned Lisu fields.
2.2. Data collection Single 0.16-ha (40 × 40 m) sample plots were selected in 7-, 12-, 21- and 28-year-old P. kesiya plantations. In each plot all vascular plant species were surveyed from October to December 1994. Identification was done directly in the field. Trees .1 cm dbh and .2 m in height were recorded. This lower size limit was chosen based on the judgment that these trees can survive even heavy grass competition and some early-season ‘cold’ fires. These trees are no longer subject to the disturbances which influence seedling mortality. Dbh was also measured in each plot by using the Bitterlich variable radius method (Mueller-Dombois and Ellenberg, 1974). Background information collected for each plantation site included previous forestry activities (weeding techniques, pruning, thinnings and extractions), ecological conditions (fire, insect infestations, grazing of cattle, storms, water levels, stream flows and wildlife) and socio-economic issues (villagers’ perceptions, income generation and non-wood forest products). For the regenerating tree species present in the plots seed dispersal mechanisms were identified. Successions of 3, 6 and 12 years of abandoned Lisu fields located on a neighboring mountain ridge were chosen as control plots. These data were published in a related study of vascular plant species composition and tree basal area by Kanjunt and Oberhauser (1996). Data collection methods and sample plot area were identical to those in this study.
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Table 2 List of vascular tree species and seed dispersal mode Tree species
Family
P. kesiya plantationa P7
Acacia concinna Actinodaphne sp. (prob. sikkimensis) Albizia chinensis Albizia lebbekoides Albizia odoratissima Albizia procera Alstonia glaucescens (Winchia callophylla) Aporusa villosa Archidendron clypearia ssp. clypearia var. clypearia Ardisia sp. Artocarpus sp. prob. rigidus ssp. asperulus Beilschmiedia sp. Berrya ammonilla Berrya mollis Bombax anceps (kerrii) Bouea oppositifolia Callicarpa arborea Calophyllum polyanthum Camellia sp. (prob. connata) Castanopsis diversifolia Castanopsis echinocarpa Castanopsis ferox Cleistanthus sp. Croton oblongifolius Dalbergia assamica Dalbergia fusca Dalbergia sp. Diospyros glandulosa Diospyros undulata (var. cratericarpa) Elaeocarpus sp. Engelhardia spicata var. spicata Erythrina seberosa Eugenia cumini Eurya acuminata Fernandoa adenophylia Ficus hirta Ficus hispida Ficus sp. Fragraria fragrans Glochidion sp. Glochidion sp. Gluta usitata Gmelia arborea Grewia disperma Haldina cordifolia
Leg/Mimosoideae Lauraceae Leg/Mimosoideae Leg/Mimosoideae Leg/Mimosoideae Leg/Mimosoideae Apocynaceae Euphorbiaceae Leg/Mimosoideae
+
+
+
+
+
Elaecarpaceae Juglandaceae
+
+
+ +
+
+
Lauraceae Tiliaceae Tiliaceae Bombaceae Anacardiaceae Verbenaceae Gutifereae Theaceae Fagaceae Fagaceae Fagaceae Euphorbiaceae Euphorbiaceae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Ebenaceae Ebenaceae
P21
P28
Seed dispersal modeb
L3
w
L6
L12
+ +
Myrsinaceae Moraceae
Leg/Papillionideae Myrtaceae Theaceae Bignoniaceae Moraceae Moraceae Moraceae Potaliaceae Euphorbiaceae Euphorbiaceae Anacardiaceae Verbenaceae Tiliaceae Rubiaceae
P12
Abandoned Lisu fields
+
+ +
+ + + + +
+ + +
+
+ + +
+ +
+ + + + +
+ + + +
+ + +
+ +
+ +
+
+ +
+
+ +
+ + + +
+ + + + +
b
+ + +
+
+ +
+ +
+ +
+ +
+
+
+ + +
+ + + + + +
+ +
+ +
+ + +
+
+
+
+
+ + + +
a
+
+
+
+
+ + +
+
+
+ + + +
+
+
+
+
+ +
+ +
+ + +
+
+
+
+ +
+ + +
+
d
+
+
+ +
+ +
+ + +
+ + +
+ + +
+ + +
175
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183 Table 2 continued
Tree species
Family
P. kesiya plantationa P7
Helicia nilagirica Heliciopsis terminalis Holarrhena antidysenterica (pubescens?) Holigaria longifolia (kurzii?) Lagerstroemia venusta Lannea coromandelica Lithocarpus elegans Lithocarpus fenestratus Lithocarpus finetii Lithocarpus polystachyus Lithocarpus trachycarpus Lithocarpus vestitus Litsea monopetala Litsea sp. Mallotus cochinchinensis ( = paniculata) Mallotus philippensis var. philippensis Manglietia garrettii Markhamia stipulata Meliosma pinnata Michelia baillonii Michelia rajaniana Neocinnamomum caudatum Olea sp. Oroxylum indicum Pandanus furcatus Paramichelia baillonii Phoebe flores Phyllanthus emblica Pinus kesiya Protium serratum Prunus arborea var. montana Pyrenaria camelliiflora Rhus (Toxicodendron) rhetzoides Sarcosperma arborea Schima wallichii Sterculia sp. Sterculia sp. Stereospermum colais Stereospermum neuranthum Styrax benzoides Ternstroemia gymnanthera Toona microcarpa (ciliata) Turpinia pomifera Vitex pinnata Walsura robusta Wendlandia tinctoria ssp. floribunda Xantolis (Pouteria) cambodiana
+
Sapotaceae
P28
Seed dispersal modeb
L3
w
L6
+ +
L12
+ +
+
+
+ +
+
+ +
+
+ +
+ +
+ +
+
+ + + + +
+
+ +
+ +
+ +
+
+
+
+
+ + +
+ +
+ + + + + + + + +
+ +
a
+
+
+
b
+ +
+
+ +
+ +
d
+
+ + +
Euphorbiaceae Magnoliaceae Bignoniaceae Meliosmaceae Magnoliaceae Magnoliaceae Lauraceae Oleaceae Bignoniaceae Pandanaceae Magnoliaceae Lauraceae Euphorbiaceae Pinaceae Burseraceae Rosaceae Theaceae Anacardiaceae Sapotaceae Theaceae Sterculiaceae Sterculiaceae Bignoniaceae Bignoniaceae Styragaceae Theaceae Meliaceae Staphylaceae Verbenaceae Meliaceae Rubiaceae
P21
+ +
Protaceae Proteaceae Apocynaceae Anacardiaceae Lythraceae Anacardiaceae Fagaceae Fagaceae Fagaceae Fagaceae Fagaceae Fagaceae Lauraceae Lauraceae Euphorbiaceae
P12
Abandoned Lisu fields
+ + + + + + + +
+ +
+ +
+
+
+
+
+
+ +
+
+ + +
+
+
+ + +
+ +
+
+ + + +
+
+
+
+
+ + +
+ +
+ + + +
+ + +
+
+ + + +
+
+ + + + + +
+ + +
176
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 2 continued
Tree species
Family
P. kesiya plantationa P7
Unidentified Unidentified Unidentified Unidentified Unidentified Unidentified Small trees Alseodaphne vestitus Antidesma acidum Callicarpa rubella Canthium (Fagerlindia) horridum Ficus prostrata Glochidion acuminatum Heteropanax fragrans Litsea cubeba Maesa montana Rhus chinensis (montana) Saurauia roxburghii Symplocos sp. Wendlandia paniculata Xanthophyllum sp. Trees Percentage of spp./plot a
+ + +
Rubiaceae Unidentified Unidentified Unidentified Unidentified Unidentified
Lauraceae Euphorbiaceae Verbenaceae Rubiaceae Moraceae Euphorbiaceae Araliaceae Lauraceae Myrsinaceae Anacardiaceae Actinidiaceae Symplogaceae Rubiaceae Polygalaceae
P12
+ +
P21
+ +
+
+
+ +
13 43
47 70
Seed dispersal modeb
L3
w
L6
L12
d
+ + +
+ + +
41 57
b
a
+
+
+ +
P28
Abandoned Lisu fields
+ 45 69
+ + + +
+
+ + + + +
+
+ 4 13
19 43
+ 24 53
25
22
+ + +
+ + +
+
+
+ + + +
+ + + + +
36
+ 55
Number equals years of abandonment. w, wind; d, dehiscence; b, birds; a, all animals.
b
2.3. Data analysis Dbh data were used to calculate stem basal area per plot and per dbh class, both for P. kesiya and for other trees. Stem basal area information was used as an estimate of dominance. The floristic composition of the sample plots was compared by using Sørensen’s index of similarity (ISs) for all vascular plants. This index, which does not take into account species abundance, measures the ratio of the common species (c) to the average number of species occurring in two samples (A and B) in percent (Mueller-Dombois and Ellenberg, 1974): ISs = 2c=(A + B) × 100 Species composition in the plantation plots were also compared to the 3-, 6- and 12-year-old abandoned Lisu fields. A complementarity check, in
which the cumulative number of vascular plant species was calculated, from youngest to oldest plots was used to estimate the proportion of the local flora surveyed in the study plots (Pielou, 1995). Seed dispersal mechanisms for tree species were categorized as wind, dehiscence (seed transported over short distance without wind), birds only and all animals.
3. Results 3.1. Structural characteristics In the 7-year-old plantation P. kesiya was the dominant species. The ground was densely covered with grasses and herbs, mainly Eupatorium adenophorum. Very few seed trees still remained at the ridge on top
177
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
of the plot. Coppicing and stump regeneration were recorded in very few cases. The 12-year-old plantation site had a dense canopy
cover consisting of pines and many other tree species. Different canopy layers and tree sizes had developed among the non-pine species. Ground cover was rela-
Table 3 List of vascular shrubby species and seed dispersal mode Shrubby species
Family
P. kesiya plantationa P7
Sapindaceae Sapindaceae Myrsinaceae Compositae Urticaceae Urticaceae Urticaceae Buddlejaceae Leg/Papillionideae
Clausena excavata Clerodendrum (Volkameria) fragrans Clerodendrum serratum Clerodendrum serratum var. wallichii Desmodium sp. Euodia lepta (triphylla?) Eurya nitida Ficus subincisa Flemingia lineata Flemingia sootepensis Flemingia sp. Helicteres sp. Itea macrophylla Kydia calycina Leea indica Leea sambucina (rubra) Melastoma normale var. normale Melastoma sp. Randia sp. Sambucus javanica Sauropus sp. Securinega leucopyus Sida sp. Strobilanthes sp. Viburnum sp. Viburnum sp. Volkameria fragrans Unidentified Shrubs Percentage of spp./plot
Rutaceae Verbenaceae
+
Verbenaceae Verbenaceae
+ +
P28
L3
w
L6
+ +
b
a
+ +
+
+ +
+
+
+ + + +
+
+ +
+
+
+ +
+
3 5
+
+
+ 7 10
+ + +
+
+ +
+ 2 3
+
+ +
+
5 17
d
+
+
+ +
Melastomaceae Rubiaceae Sambucaceae Euphorbiaceae Euphorbiaceae Malvaceae Acanthaceae Caprifoliaceae Caprifoliaceae Verbenaceae Acanthaceae
L12
+
+
Leg/Papillionideae Rutaceae Theaceae Moraceae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Sterculiaceae Iteaceae Malvaceae Leeaceae Leeaceae Melastomaceae
Number equals years of abandonment. w, wind; d, dehiscence; b, birds; a, all animals.
b
P21
Seed dispersal modeb
+
Allophyllus cobbe Allophyllus sootepensis Ardisia sp. Blumea balsamifera Boehmeria chiamaiensis Boehmeria sp. Boehmeria sp. Buddleja asiatica Cajanus cajan
a
P12
Abandoned Lisu fields
8 26
10 23
+ +
5 11
0
2
2
2
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 4 List of vascular climber plant (inc. woody climbers, vines) and seed dispersal mode Climber species
Family
P. kesiya plantationa P7
Acacia comosa Acacia megaladena Argyreia sp. Argyreia speciosa ( = nervosa) Asparagus filicifolia Clematis smilacifolia Connarus sp., prob. semidecadendrus Dalbergia foliacea Dalbergia volubilis Derris sp. Derris sp. Dioscorea alata Dioscorea pentaphylla Diploclisia glaucescens Embelia ribes Embelia stricta Heterosmilax sp. Jasminum bifarium Maytenus marcanii Maytenus sp. Millettia extensa Mucuna pruriens Mussaenda sanderiana Paederia sp. Passiflora siamensis Piper sp. Pueraria sp. Rubus alceifolius Rubus sp. Shuteria sp. Shuteria sp. Smilax lanceifolia Smilax ovalifolia Smilax perfoliata Smilax sp. Smilax sp. Spatholobus compar Spatholobus sp. Tetrastigma sp. Thunbergia grandiflora Urena lobata Unidentified Unidentified Unidentified Climbers Percentage of spp./plot
P21
P28
Seed dispersal modeb
L3
w
d
b
a
0
0
0
0
+
Leg/Mimosoideae Leg/Mimosoideae Convolvulaceae Convolvulaceae
+
L6
+
+
+
+ +
+
+
+
+ +
+ + + + +
+
+
5 17
+ +
7 10
+ +
+
+ + + +
+
+ + 12 17
+
+
+
+
+ +
+
+ +
+
+ + +
+
+
+
+
+ +
+ +
L12
+
+
Liliaceae Ranunculaceae Connaraceae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Dioscoreaceae Dioscoreaceae Menispermaceae Myrsinaceae Myrsinaceae Smilacaceae Oleaceae Celastraceae Celastraceae Leg/Papillionideae Leg/Papillionideae Rubiaceae Rubiaceae Passifloraceae Piperaceae Leg/Papillionideae Rosaceae Rosaceae Leg/Papillionideae Leg/Papillionideae Smilacaceae Smilacaceae Smilagaceae Smilacaceae Smilagaceae Leg/Papillionideae Leg/Papillionideae Vitaceae Thunbergiaceae Malvaceae Leguminosae Leguminosae Leguminosae
P12
Abandoned Lisu fields
7 11
9 29
5 11
9 20
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183 Table 5 List of vascular herbs (inc. ferns), grasses and unidentified species and seed dispersal mode Family
P. kesiya plantationa P7
Herbs (incl. ferns) Alpinia (Zingiber) zerumbet Alpinia bracteata Alpinia sp. Alpinia sp. Artemesia dubia Artemesia roxburghiana Compositae sp. Costus laeta Crotalaria sp. Curculigo recurvata ( = Molineria capitulata) Curculigo sp. prob. latifolia Eupatorium (Ageratina) adenophorum Eupatorium (Chromolaena) odoratum Gerbera perperasum Polygonum chinense Pteridium aquilinum var. wightianum Scleria perpurascens Thelypteris sp. Unidentified Vernonia cinerea Vernonia sp. Herbs Percentage of spp./plot Grasses Imperata cylindrica Microstegium vagans Neyraudia reynaudiana Panicum montanum Panicum sp. Setaria glauca Setaria palmifolia Thysanolaena latifolia Unidentified Unidentified Grasses Percentage of spp./plot Unidentified species Unidentified Unidentified Unidentified Percentage of spp./plot
Zingiberaceae
P12
+
P21
+
Hypoxidaceae
+
w
d
b
a
0
0
0
0
+
+
L6
+
+
+
+
+ + +
4 13
+ +
+ +
+
+ +
+
6 9
+
+
3 10
+ + +
+
+
1 1
2 3
+
+
+
+
+
+ +
+
8 11
+
+
+ 4 6
+ + + + + 5 8
0 0
0 0
0 0
+
6 19
+ 5 11
5 11
+
+
+
+ + +
+ + +
4 13
3 7
2 4
0
0
0
0
0 0
+ + 2 5
0 0
0
0
0
0
Unidentified Unidentified 0 0
L12
+
+
Cyperaceae Thelypteridaceae Unidentified Compositae Compositae
Poaceae Gramineae Gramineae Gramineae Gramineae Gramineae Gramineae Gramineae Graminae Graminae
L3
+
Compositae Compositae Polygonaceae Dennstaedtiaceae
Seed dispersal modeb
+
Zingiberaceae Zingiberaceae Zingiberaceae Compositae Compositae Compositae Costaceae Leg/Papillionideae Hypoxidaceae
Compositae
P28
Abandoned Lisu fields
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 5 continued
Family
Total number of species (Tables 2–5) a
P. kesiya plantationa
Abandoned Lisu fields
Seed dispersal modeb w
P7
P12
P21
P28
L3
L6
L12
30
67
72
65
31
44
45
d
b
a
Number equals years of abandonment. w, wind; d, dehiscence; b, birds; a, all animals.
b
tively light. No pine regeneration was observed, whereas other trees had regenerated well and were regularly distributed throughout the plot. A small number of native seed trees were left at the top of the ridge outside of the plot. Stump regeneration and coppicing were observed more frequently than in all other plots. In the 21-year-old plantation some pine mortality was noted. Many tree seedlings were recorded in a ground cover dominated by E. adenophorum. The middle canopy was almost absent. Many climbers were recorded. There were no seed trees left in or outside the plot. Coppicing and stump regeneration was not obvious. The 28-year-old plantation stand was dominated by P. kesiya, but was structurally rich in species, canopy layers and tree sizes. A relatively high number of standing pines had died very recently of uncertain causes. Ground cover was light. There were no old seed trees left in or surrounding the plot. Very few species were observed growing from old stumps or were coppicing. The 3- and 6-year-old abandoned Lisu fields more closely resembled grassland than secondary forest, with scattered shrubs and trees. The succession in the 12-year-old Lisu abandoned field showed rather scattered trees with small crowns, the ground being covered with Imperata cylindrica grass. The stem basal area of P. kesiya and of tree species combined increased with age from the 7- to the 21year-old stands and declined in the 28-year-old plot, due perhaps to the extraction of approximately 40% of the pines in this plot at the age of 20. The stem basal area of other trees in the plantation plots varied between 1.88 and 7.75 m2/ha, with a peak in the 12year-old plot. In the abandoned Lisu field plots the stem basal area increased from 0 to 7.94 m2/ha from the 3-year-old to the 12-year-old plot (Fig. 1). For the stem basal area, the Bitterlich variable radius method
measurement of larger samples gives an indication of how plot data represents a whole stand (Kramer and Akc¸a, 1982). The 7-, 21- and 28-year-old plantation plots seemed to show statistically correct results, as the ratio of plot data to Bitterlich data was below 10%. For the 12-year-old plantation the stem basal area of pines and of other trees collected as plot data was not similar enough to the Bitterlich measurements to allow this plot to be representative of the whole 12-year-old stand. In fact, the Bitterlich data showed that the 12year-old plantation plot data overestimated the stem basal area of other trees, but underestimated the stem basal area of pines. However, Fig. 1 shows the Bitterlich measurements of the stem basal area at dbh for the pine plantation plots and the abandoned Lisu fields. The ratio of pines to other tree species is an indication of the degree of stand dominance by non-pine species. Fig. 2 shows the number of trees per ha for the plantation plots of different ages and for the abandoned Lisu fields plots. The density of P. kesiya declined with increasing age of the pine stands whereas the density of all other tree species increased with time, both in the plantations and the abandoned Lisu fields. The 12-year-old plantation was almost five times higher in density of tree individuals than the non-planted one. 3.2. Species composition and diversity The number of trees andthe number of tree species was low in the 7-year-old plantation plot (13 tree spp.) and in all abandoned Lisu field plots (4–24 tree spp.), but almost equally high in the 12-, 21- and the 28-year-old plantation plots (41–47 tree spp.), respectively, showing the highest numbers (47 tree spp.) in the 12-year-old plantation plot (Tables 2, 3, 4 and 5). Most tree species common in the 12-, 21- and 28-year-old plantation plots, such as Alstonia glaucescens, Berrya mollis, Engel-
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183 Table 6 Sørensen’s index of similarity (ISs) for all vascular plant species in P. kesiya plantations and in natural succession plots in abandoned Lisu fields P21 P12 P7 L12 L6 L3
35 35 19 18 13 13 P28
35 23 14 9 6 P21
22 18 18 10 P12
13 14 33 P7
22 18 L12
24 L6
P, P. kesiya plantation; L, natural succession in abandoned Lisu fields; numbers indicate years after afforestation/length of abandonment.
hardia spicata, Eugenia cumini, Ficus hirta, Gluta, Michelia baillonii, Phyllanthus emblica and Schima wallichii, have mostly pioneer characteristics, but are components of the potential forest types at that elevation and soil condition. These tree species are widely distributed in the survey area. Most of these species were lacking in the abandoned Lisu fields. Fagaceae species, mainly Castanopsis and Lithocarpus species,were once common in the different types of oak forests of the region. Six Fagaceae species were recorded in the 12year-old plantation plot, three and two in the 21- and 28year-old plots, respectively, and none in all other plots. Climber species were rarely common to two or more plots. Eupatorium adenophorum, a herb, was found in every plot. Most grass species (five) were recorded in the 28-year-old plantation. Four grass species were found in the 6-year-old abandoned Lisu fields and three grass species were found in both the 7-year-old plantation and the 3-year-old abandoned Lisu fields. Grass species made up 13% of all species in this plot, indicating a grass dominated area. A list of all species, categorized by life form, is presented in Tables 2–5. Sørensen’s index of similarity (ISs) values ranged from 6 to 35 among plots. The ISs values comparing the plantation plots with the abandoned Lisu fields were very low (6–18), except for the 3-year-old abandoned Lisu field compared to the 7-year-old plantation (ISs = 33). Intermediate ISs values of 35 were found for comparisons of the 12-, 21- and 28-yearold plantation plots. Comparisons among the Lisu fields also showed relatively low ISs values, indicating a low degree of similarity in species composition among them (Table 6). Species composition was also investigated through
181
a complementarity check. In seven plots totalling 1.12 ha, the fraction of locally available species found still seems small, as the cumulative number of species was still increasing from 197 species in the sixth plot to 216 species in the seventh plot (Fig. 3). In other words, 19 out of 45 species (42%) in the 12-yearold abandoned Lisu field were not surveyed previously. Newly listed species declined slowly from 58 to 38, 28, 23, 23 and finally 19 (Fig. 3). With 216 species of vascular plants and 112 tree species recorded in seven plots covering 1.12 ha, species diversity is apparently quite high in the survey area. 3.3. Seed dispersal Old seed trees growing in the plantations were rare in the vicinity of the stands studied. The majority of tree species, 55 out of 104, were dispersed by animals of all kinds. Thirty-six out of these 55 tree species were dispersed by birds. Seed dispersal characteristics were not obtained for 14 tree species. Animal dispersed tree species were more frequent in the plantation plots. In the 3-, 6- and 12-year-old abandoned Lisu fields 50, 42 and 46%, respectively, were dispersed by animals. In the 7-, 12-, 21- and 28-yearold plantations 46, 57, 56 and 51%, respectively, were dispersed by animals. Most tree species of the potential lower montane oak and pine-oak forests (e.g. Fagaceae and some Myrsinaceae and Moraceae spp.) are dispersed by animals. These trees were almost exclusively found in the 12-, 21- and 28-
Fig. 3. Complementarity of vascular plant species in 7-, 12-, 21and 28-year-old P. kesiya plantation plots and in 3-, 6- and 12-yearold abandoned Lisu fields. The plot size is 1600 m2 for all plots.
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Table 7 Number of tree species according to seed dispersal mode in P. kesiya plantations and in natural succession plots in abandoned Lisu fields
P7 P12 P21 P28 L3 L6 L12 Total no. of tree species
Wind
Dehiscence
Birds only
All animals
No. tree spp.
5 10 11 13 1 5 10 25
3 9 5 13 1 3 5 22
4 14 17 16 1 6 9 36
6 27 23 22 2 8 11 55
13 47 41 45 4 19 24 112a
P, Pinus kesiya plantation; L, natural succession in Lisu abandoned fields; numbers indicate years after afforestation/length of abandonment. a Manner of seed dispersal not identified for 14 species.
year-old plantation plots, while relatively few were found in the 12-year-old abandoned Lisu fields (Table 7).
4. Discussion Twenty-eight years after plantation of P. kesiya on abandoned swidden plots a well structured forest had developed. The 12-year-old plantation site was much better developed with respect to structure and species diversity than the abandoned Lisu agricultural site of the same age. The stem basal area was almost twice as high. Species composition of the 12-year-old plantation plot seemed to be closer to the potential forest type than the 12-year-old abandoned Lisu fields. It appears that the declining stem basal area of P. kesiya trees from the 21-year-old plantation to the 28year-old plantation was replaced by the stem basal area of other tree species. Secondary diseases seemed to be of no importance in pine afforestations until the age of 20. After that, dying pines may even contribute to enhanced natural succession by creating gaps, similar to the logging operations in the 28-year-old plot which had reduced the stem basal area. Many of the tree species found in the plots were in fact tree seedlings or very small saplings which may or may not survive this stage. All plots showed a rather sharp decline in the number of individuals
and species with higher dbh, prolonged in the 28year-old plantation plot. It seemed as if other trees couldn’t survive at a sufficient rate as the plantations grew older. This suggests that creating gaps of various sizes, as was done in the 28-year-old plot, eventually leads to better structured stands. Koop and Siebel (1993) have already tried various conversion management measures in temperate forest plantations with promising results. It would be useful to apply and monitor different silvicultural treatments in tropical environments to validate this hypothesis. The cutting of pines might then not only benefit the regeneration process, but also generate economic benefits. Eupatorium adenophorum, E. odoratum, Polygonum chinense and Pteridium aquilinum were found in most plots, indicating severe disturbances of the survey sites. The number of vascular plant species and the number of tree species in the plantation plots was much higher than in the succession on abandoned Lisu fields, indicating that reforestation of severely disturbed areas with P. kesiya might indeed speed up the successional process and allow new species to thrive. It was shown that the fraction of species found in seven plots (total area of 1.12 ha) is far from complete for the area surveyed. The overall number of tree species found (112) is very high, indicating an area of high diversity (Elliott et al., 1989). The study revealed that birds and other animals contribute to forest regeneration as seed dispersers. Parrotta (1993) has observed a significant negative correlation between seedling density and distance to the nearest possible seed source. However, as seed trees were scarce in the vicinity of the plots, animals must have carried the seeds from far away. Ewel (1983) has stated that the high net productivity of successional ecosystems supports large animal populations. This suggests that an important role of pine plantations in the natural regeneration process induces habitat as well as plant composition interactions. Feeding, breeding and roosting visits alone provide opportunities for seed dispersal. Two possible ways of enhancing regeneration are proposed, i.e. effective wildlife protection and habitat development such as the planting of species attractive to animals to lure them into the plantation. The regeneration process of forests is always subject to disturbances. It is important to know which
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
disturbances prevail in a given surrounding to protect the regeneration from damage. For the study site the development of new agricultural methods is a permanent threat, which could be addressed by participatory land use planning methods (Limchoowong and Oberhauser, 1996). It is nowadays widely accepted that uncontrolled fires as another widespread disturbance cause severe damage to the highland ecosystem, although not all interrelations are yet fully understood (Elliott et al., 1989). One important aspect is that once a previously damaged area burns the successional development starts again at a very early stage. Any restoration through plantation has to take these disturbances and the social and cultural implications into account. Acknowledgements This study was conducted during a 3-year term of development assistance by the German Development Service (DED) to the Thai-UN Sam Muen – Highland Development Project. The author wishes to express his gratitude to Mr Samer Limchoowong, former director of the Thai-UN Sam Muen – Highland Development Project. He supported this study from its initiation until the end. The author also wishes to thank the late Dr Tem Smitinand, retired director of the Royal Forest Departments’ herbarium, for his field plant identification. Dr James F. Maxwell provided invaluable help in identifying seed dispersal mechanisms and cross-checking species. The staff of Watershed Development Unit Khun Khong and of the Sam Muen Project, Royal Forest Department, were extremely helpful in providing facilities and support for the study. Many thanks to Mr Bradford Withrow-Robinson for his critical comments and editing of the manuscript. References Elliott, S., Maxwell, J.F. and Beaver, O.P., 1989. A transect survey of monsoon forest in Doi Suthep-Pui National Park. Nat. Hist. Bull. Siam Soc., 37: 137–171.
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Ewel, J., 1983. Succession. In: F.B. Golley (Editor), Tropical Rain Forest Ecosystems, A. Structure and Function. Elsevier, Amsterdam, pp. 217–223. Kanjunt, C. and Oberhauser, U., 1996. Successional forest development in abandoned swidden plots of Lisu, Hmong and Karen ethnic groups (in Thai – English version available through authors). In: B. Boontawee (Editor), Supplementary Papers of the National Forestry Conference 1995 A century of Forestry in Thailand. RFD, Bangkok, pp. 129–133. Kijkar, S., 1987. Pines in Thailand. Silviculture Branch. RFD, Bangkok (in Thai). Koop, H. and Siebel, H.N., 1993. Conversion management towards more natural forests: evaluation and recommendations. In: M.E.A. Broekmeyer, W. Vos and H. Koop (Editors), European Forest Reserves. Pudoc, Wageningen, pp. 199–201. Koskela, J., Kuusipalo, J. and Sirikul, W., 1995. Natural regeneration dynamics of Pinus merkusii in northern Thailand. For. Ecol. Manage., 77: 169–179. Kramer, H. and Akc¸a, A., 1982. Leitfaden fuer Dendrometrie und Bestandesinventur. J.D. Sauerla¨nder’s Verlag, Frankfurt am Main, 251 pp. (in German). Limchoowong, S. and Oberhauser, U., 1996. Can villagers manage the highland resources. In: F. Turkelboom, K. Van Look-Rothschild and K. Van Keer (Editors), Highland Farming: Soil and the Future, pp. 16–18, Soil Fertility Conservation Project, Maejo University Thailand – Catholic University of Leuven, Belgium, pp. 13–22. Mueller-Dombois, D. and Ellenberg, H., 1974. Aims and Methods of Vegetation Ecology. Wiley, New York, 547 pp. Parrotta, J.A., 1993. Secondary forest regeneration on degraded tropical lands: the role of plantations as ‘foster ecosystems’. In: H. Lieth and M. Lohmann (Editors), Restoration of Tropical Ecosystems. Kluwer, Dordrecht, pp. 63–73. Phugjaroon, W. and Kaewamphut, T., 1993. Structure of a Hill Evergreen Forest at Watershed Development Unit 26, Chiang Mai Province. Research Section, Watershed Management Division, RFD, Bangkok, 41 pp. (in Thai with English abstract). Pielou, E.C., 1995. Biodiversity versus old-style diversity: measuring biodiversity for conservation. In: T.J.B. Boyle and B. Boontawee, (Editors), Measuring and Monitoring Biodiversity in Tropical and Temperate Forests. CIFOR, Bogor, pp. 5–17. RFD, 1993. Statistics of Forest in Thailand. Planning division, RFD, Bangkok. Santisuk, T., 1988. An account of the vegetation of northern Thailand. Geoecological Research 5, Franz Steiner Verlag Wiesbaden GmbH, Stuttgart, 103 pp. Werner, W.L., 1996. Pinus in Thailand. Geoecological Research 7, Franz Steiner Verlag Wiesbaden GmbH, Stuttgart, 287 pp. (in German).
Secondary forest regeneration beneath pine (Pinus kesiya) plantations in the northern Thai highlands: a chronosequence study Ulrich Oberhauser* John-F.-Kennedy-Str. 41, 73037 Goeppingen, Germany Accepted 9 May 1997
Abstract Northern Thailand has witnessed rapid and extensive forest loss over the past 30 years for many reasons. In response to this, the Royal Forest Department has pursued a highland reforestation program which has led to 1500 km2 of established Pinus kesiya plantations. Present forest management objectives, however, favor more natural mixed forests. Research was carried out in a highland area (1400 km2) of Chiang Mai Province in order to answer the following questions. Does planting of P. kesiya on abandoned agricultural areas effect the rate of natural forest succession? How do these plantations change structurally through the years? Four pine plantations, aged 7, 12, 21 and 28 years, similar in stand and site conditions, were selected and also compared to unplanted regenerating fields aged 3, 6 and 12 years. Basal area, distribution of trees, species composition, diversity and seed dispersal mechanisms were examined. Results of the study revealed a high number of vascular species in the 12-, 21- and 28-year-old plots. An increasingly complex forest structure could be observed as mid- and low-level canopies had developed and other species replaced pines in the overstorey. Increasing numbers of animal dispersed tree species became established in the older plantations. Recovery of woody vegetation was faster in plantations than in areas not afforested with P. kesiya. Over time, the basal stem area of pines which had died or had been cut was replaced by the basal area of other tree species. It appears that P. kesiya plantations can enhance establishment of mixed forests. The implications of afforestations with pine, stand management practices, such as density and fire management, wildlife enhancement and possible disturbances, are also discussed. 1997 Elsevier Science B.V. Keywords: Pinus kesiya; Natural regeneration; Plantation; Diversity; Conversion management
1. Introduction During the years from 1961 to 1991, forest cover in Thailand decreased from 53 to 26.7%. This has occurred despite various measures undertaken by the Royal Thai Government, such as banning of logging concessions, establishing protected areas (including National Parks and Wildlife Sanctuaries) and launching reforestation programs. The northern mountains are of major importance to Thailand’s development. * Tel.: +49 7161 68281; fax: +49 7161 927316.
They are the watershed for the four major rivers forming the Chao Phraya river that supplies the Central Plain, Thailand s center of rice production and Bangkok metropolis. The current goal of the Royal Forest Department (RFD) is to achieve 40% forest cover nationwide, of which 28% is to be in protected areas. Most northern watersheds are located in this protected area system. It is estimated that about 320 km2 of forest area is destroyed every year in the north, mainly by forest fires, logging and swidden cultivation. In the 1960s the RFD promoted establishment of Pinus kesiya plantations. Initially on a limited scale,
0378-1127/97/$17.00 1997 Elsevier Science B.V. All rights reserved PII S0378-1127 (97 )0 0203-X
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 1 Characteristics of study plots in P. kesiya plantations and in natural succession plots in abandoned Lisu fields Plot codea
Altitude (masl)
Slope (%)
Aspect
Soil
P. kesiya (no./plot)
Vegetative cover
P7 P12 P21 P28 L3 L6 L12
1290 1330 1320 1250 1200 1200 1200
47 49 43 50 25 35 50
E E N-E E E S-W S
Podzolic Podzolic Podzolic Podzolic Podzolic Podzolic Podzolic
98 45 82 33 0 0 0
Plantation/weed/grass Plantation/forest Plantation/forest Forest Grasses and climbers Weed, shrub Shrub, saplings
a
P, P. kesiya plantation; L, natural succession in abandoned Lisu fields; numbers indicate years after plantation/length of abandonment.
this effort was expanded in the 1970s and carried out by 113 Watershed Development Units. As a result, approximately 1500 km2 of P. kesiya plantations in northern Thailand are now covered with these pine plantations (RFD, 1993). P. kesiya is a three-needled pine native to Thailand. It is one of the most intensively studied tree species in Thailand (Kijkar, 1987; Koskela et al., 1995; Werner, 1996). The provenances used are usually of local origin. This species occurs naturally in two distinct vegetation types, i.e. lower montane pine-oak forest and pine-deciduous dipterocarp forest (Santisuk, 1988). The latter has rarely been converted to agriculture or to pine plantations. Lower montane pine-oak forest may be considered a severely disturbed stage of a lower montane oak forest influenced by biotic (burning, grazing, cutting) or edaphic factors. It is best developed on elevations ranging from 1000–1400 m, though some pines can be found as low as 600 m and as high as 1900 m. The pines in the lower montane pine-oak forest are up to 40 m tall and grow mostly on ridges and on steep slopes. It is the climax type on many afforestation sites. P. kesiya thrives well on red to yellow granitic soil types (Santisuk, 1988). Today, a mixture of species is used in most afforestations. The more common species on higher elevations are Prunus ceraoides, Docynia indica, Betula alnoides and Schima wallichii. However, P. kesiya still makes up some 50% of all trees planted today. This study aimed to evaluate the potential of P. kesiya afforestations as catalysts for natural forest regeneration. The current management goal is to establish diverse, site adapted, multistory and sustainably manageable forests which fulfill watershed functions with little damage to the environment. Can this be achieved
within a reasonable length of time by planting pines on severely disturbed and degraded sites in watershed areas?
2. Materials and methods 2.1. Site description The study site was located in Watershed Development Unit No. 26, Khun Khong, on a mountain ridge between the Taeng and Ping rivers 100 km north of Chiang Mai, in the districts of Chiang Dao and Wiang Haeng, Chiang Mai Province in northern Thailand. Soils were sandy to loamy lateritic podsols. These types of soil cover vast areas of the highlands in the western parts of northern Thailand. The entire area is mountainous with an altitude of 1100–1500 m. Average temperatures range between 10 and 27°C, with occasional frosts. Average annual rainfall is approximately 2000 mm which falls within a 5-month period (Phugjaroon and Kaewamphut, 1993). The study site is in an area formerly cultivated by Lisu people, whose agricultural practices are commonly classified as ‘long cultivation – very long fallow’. In this cultivation system forest is cleared and cultivated for several years before being abandoned due to declining soil fertility, increasing weed pressure and erosion. Grasses and herbs soon cover abandoned fields which regenerate very slowly and are prone to wild fires. In 1965 the Royal Forest Department planted the first pines in areas where the forests were already destroyed in order to produce wood for the developing paper industry. In 1973 the Watershed Management Division took over and continued to grow pines to
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
protect and rehabilitate watersheds. Today Khun Khong has some of the oldest native pine plantations in mainland Southeast Asia. The afforestation activities resulted in 3724 ha of man-made forests in Khun Khong. The annual reforestation area for the 7-, 12-, 21- and 28-year-old plantations were 89, 128, 80 and 80 ha, respectively. Prior to afforestation the study site was subject to three different kinds of disturbances. The first disturbance, grazing, hunting and some burning, led to a lower montane pine-oak forest. The second and most severe disturbance was the clearing of the forest for agriculture which left only a few seed trees and eliminated most coppicing species. The third was frequent and ongoing disturbance by fire, cattle and tree cutting. The initial spacing of the pine trees was 4 × 4 m. There were no major differences in site preparation during the planting program. Native trees were never cut intentionally and fire was not used during site preparation. In the first 3 years after planting, weeding was carried out in a combination of strip and local point weeding. In all activities the workers were instructed to retain native trees. No fires were recorded in the 7- and 12-year-old plots, however, the 21- and 28-year-old sites each had a ground fire (Phugjaroon, pers. commun.). The plots were chosen so as to be as similar as possible concerning soil, aspect, altitude, slope and all other relevant charac-teristics, of which Table 1 gives a short overview.
Fig. 1. Stem basal area of P. kesiya and other tree species in 7-, 12-, 21- and 28-year-old P. kesiya plantations (Bitterlich method) and in 3-, 6- and 12-year-old abandoned Lisu fields (plot data).
173
Fig. 2. Number of P. kesiya and other tree species in 7-, 12-, 21and 28-year-old P. kesiya plantation plots and in 3-, 6- and 12-yearold abandoned Lisu fields.
2.2. Data collection Single 0.16-ha (40 × 40 m) sample plots were selected in 7-, 12-, 21- and 28-year-old P. kesiya plantations. In each plot all vascular plant species were surveyed from October to December 1994. Identification was done directly in the field. Trees .1 cm dbh and .2 m in height were recorded. This lower size limit was chosen based on the judgment that these trees can survive even heavy grass competition and some early-season ‘cold’ fires. These trees are no longer subject to the disturbances which influence seedling mortality. Dbh was also measured in each plot by using the Bitterlich variable radius method (Mueller-Dombois and Ellenberg, 1974). Background information collected for each plantation site included previous forestry activities (weeding techniques, pruning, thinnings and extractions), ecological conditions (fire, insect infestations, grazing of cattle, storms, water levels, stream flows and wildlife) and socio-economic issues (villagers’ perceptions, income generation and non-wood forest products). For the regenerating tree species present in the plots seed dispersal mechanisms were identified. Successions of 3, 6 and 12 years of abandoned Lisu fields located on a neighboring mountain ridge were chosen as control plots. These data were published in a related study of vascular plant species composition and tree basal area by Kanjunt and Oberhauser (1996). Data collection methods and sample plot area were identical to those in this study.
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 2 List of vascular tree species and seed dispersal mode Tree species
Family
P. kesiya plantationa P7
Acacia concinna Actinodaphne sp. (prob. sikkimensis) Albizia chinensis Albizia lebbekoides Albizia odoratissima Albizia procera Alstonia glaucescens (Winchia callophylla) Aporusa villosa Archidendron clypearia ssp. clypearia var. clypearia Ardisia sp. Artocarpus sp. prob. rigidus ssp. asperulus Beilschmiedia sp. Berrya ammonilla Berrya mollis Bombax anceps (kerrii) Bouea oppositifolia Callicarpa arborea Calophyllum polyanthum Camellia sp. (prob. connata) Castanopsis diversifolia Castanopsis echinocarpa Castanopsis ferox Cleistanthus sp. Croton oblongifolius Dalbergia assamica Dalbergia fusca Dalbergia sp. Diospyros glandulosa Diospyros undulata (var. cratericarpa) Elaeocarpus sp. Engelhardia spicata var. spicata Erythrina seberosa Eugenia cumini Eurya acuminata Fernandoa adenophylia Ficus hirta Ficus hispida Ficus sp. Fragraria fragrans Glochidion sp. Glochidion sp. Gluta usitata Gmelia arborea Grewia disperma Haldina cordifolia
Leg/Mimosoideae Lauraceae Leg/Mimosoideae Leg/Mimosoideae Leg/Mimosoideae Leg/Mimosoideae Apocynaceae Euphorbiaceae Leg/Mimosoideae
+
+
+
+
+
Elaecarpaceae Juglandaceae
+
+
+ +
+
+
Lauraceae Tiliaceae Tiliaceae Bombaceae Anacardiaceae Verbenaceae Gutifereae Theaceae Fagaceae Fagaceae Fagaceae Euphorbiaceae Euphorbiaceae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Ebenaceae Ebenaceae
P21
P28
Seed dispersal modeb
L3
w
L6
L12
+ +
Myrsinaceae Moraceae
Leg/Papillionideae Myrtaceae Theaceae Bignoniaceae Moraceae Moraceae Moraceae Potaliaceae Euphorbiaceae Euphorbiaceae Anacardiaceae Verbenaceae Tiliaceae Rubiaceae
P12
Abandoned Lisu fields
+
+ +
+ + + + +
+ + +
+
+ + +
+ +
+ + + + +
+ + + +
+ + +
+ +
+ +
+
+ +
+
+ +
+ + + +
+ + + + +
b
+ + +
+
+ +
+ +
+ +
+ +
+
+
+ + +
+ + + + + +
+ +
+ +
+ + +
+
+
+
+
+ + + +
a
+
+
+
+
+ + +
+
+
+ + + +
+
+
+
+
+ +
+ +
+ + +
+
+
+
+ +
+ + +
+
d
+
+
+ +
+ +
+ + +
+ + +
+ + +
+ + +
175
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183 Table 2 continued
Tree species
Family
P. kesiya plantationa P7
Helicia nilagirica Heliciopsis terminalis Holarrhena antidysenterica (pubescens?) Holigaria longifolia (kurzii?) Lagerstroemia venusta Lannea coromandelica Lithocarpus elegans Lithocarpus fenestratus Lithocarpus finetii Lithocarpus polystachyus Lithocarpus trachycarpus Lithocarpus vestitus Litsea monopetala Litsea sp. Mallotus cochinchinensis ( = paniculata) Mallotus philippensis var. philippensis Manglietia garrettii Markhamia stipulata Meliosma pinnata Michelia baillonii Michelia rajaniana Neocinnamomum caudatum Olea sp. Oroxylum indicum Pandanus furcatus Paramichelia baillonii Phoebe flores Phyllanthus emblica Pinus kesiya Protium serratum Prunus arborea var. montana Pyrenaria camelliiflora Rhus (Toxicodendron) rhetzoides Sarcosperma arborea Schima wallichii Sterculia sp. Sterculia sp. Stereospermum colais Stereospermum neuranthum Styrax benzoides Ternstroemia gymnanthera Toona microcarpa (ciliata) Turpinia pomifera Vitex pinnata Walsura robusta Wendlandia tinctoria ssp. floribunda Xantolis (Pouteria) cambodiana
+
Sapotaceae
P28
Seed dispersal modeb
L3
w
L6
+ +
L12
+ +
+
+
+ +
+
+ +
+
+ +
+ +
+ +
+
+ + + + +
+
+ +
+ +
+ +
+
+
+
+
+ + +
+ +
+ + + + + + + + +
+ +
a
+
+
+
b
+ +
+
+ +
+ +
d
+
+ + +
Euphorbiaceae Magnoliaceae Bignoniaceae Meliosmaceae Magnoliaceae Magnoliaceae Lauraceae Oleaceae Bignoniaceae Pandanaceae Magnoliaceae Lauraceae Euphorbiaceae Pinaceae Burseraceae Rosaceae Theaceae Anacardiaceae Sapotaceae Theaceae Sterculiaceae Sterculiaceae Bignoniaceae Bignoniaceae Styragaceae Theaceae Meliaceae Staphylaceae Verbenaceae Meliaceae Rubiaceae
P21
+ +
Protaceae Proteaceae Apocynaceae Anacardiaceae Lythraceae Anacardiaceae Fagaceae Fagaceae Fagaceae Fagaceae Fagaceae Fagaceae Lauraceae Lauraceae Euphorbiaceae
P12
Abandoned Lisu fields
+ + + + + + + +
+ +
+ +
+
+
+
+
+
+ +
+
+ + +
+
+
+ + +
+ +
+
+ + + +
+
+
+
+
+ + +
+ +
+ + + +
+ + +
+
+ + + +
+
+ + + + + +
+ + +
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 2 continued
Tree species
Family
P. kesiya plantationa P7
Unidentified Unidentified Unidentified Unidentified Unidentified Unidentified Small trees Alseodaphne vestitus Antidesma acidum Callicarpa rubella Canthium (Fagerlindia) horridum Ficus prostrata Glochidion acuminatum Heteropanax fragrans Litsea cubeba Maesa montana Rhus chinensis (montana) Saurauia roxburghii Symplocos sp. Wendlandia paniculata Xanthophyllum sp. Trees Percentage of spp./plot a
+ + +
Rubiaceae Unidentified Unidentified Unidentified Unidentified Unidentified
Lauraceae Euphorbiaceae Verbenaceae Rubiaceae Moraceae Euphorbiaceae Araliaceae Lauraceae Myrsinaceae Anacardiaceae Actinidiaceae Symplogaceae Rubiaceae Polygalaceae
P12
+ +
P21
+ +
+
+
+ +
13 43
47 70
Seed dispersal modeb
L3
w
L6
L12
d
+ + +
+ + +
41 57
b
a
+
+
+ +
P28
Abandoned Lisu fields
+ 45 69
+ + + +
+
+ + + + +
+
+ 4 13
19 43
+ 24 53
25
22
+ + +
+ + +
+
+
+ + + +
+ + + + +
36
+ 55
Number equals years of abandonment. w, wind; d, dehiscence; b, birds; a, all animals.
b
2.3. Data analysis Dbh data were used to calculate stem basal area per plot and per dbh class, both for P. kesiya and for other trees. Stem basal area information was used as an estimate of dominance. The floristic composition of the sample plots was compared by using Sørensen’s index of similarity (ISs) for all vascular plants. This index, which does not take into account species abundance, measures the ratio of the common species (c) to the average number of species occurring in two samples (A and B) in percent (Mueller-Dombois and Ellenberg, 1974): ISs = 2c=(A + B) × 100 Species composition in the plantation plots were also compared to the 3-, 6- and 12-year-old abandoned Lisu fields. A complementarity check, in
which the cumulative number of vascular plant species was calculated, from youngest to oldest plots was used to estimate the proportion of the local flora surveyed in the study plots (Pielou, 1995). Seed dispersal mechanisms for tree species were categorized as wind, dehiscence (seed transported over short distance without wind), birds only and all animals.
3. Results 3.1. Structural characteristics In the 7-year-old plantation P. kesiya was the dominant species. The ground was densely covered with grasses and herbs, mainly Eupatorium adenophorum. Very few seed trees still remained at the ridge on top
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
of the plot. Coppicing and stump regeneration were recorded in very few cases. The 12-year-old plantation site had a dense canopy
cover consisting of pines and many other tree species. Different canopy layers and tree sizes had developed among the non-pine species. Ground cover was rela-
Table 3 List of vascular shrubby species and seed dispersal mode Shrubby species
Family
P. kesiya plantationa P7
Sapindaceae Sapindaceae Myrsinaceae Compositae Urticaceae Urticaceae Urticaceae Buddlejaceae Leg/Papillionideae
Clausena excavata Clerodendrum (Volkameria) fragrans Clerodendrum serratum Clerodendrum serratum var. wallichii Desmodium sp. Euodia lepta (triphylla?) Eurya nitida Ficus subincisa Flemingia lineata Flemingia sootepensis Flemingia sp. Helicteres sp. Itea macrophylla Kydia calycina Leea indica Leea sambucina (rubra) Melastoma normale var. normale Melastoma sp. Randia sp. Sambucus javanica Sauropus sp. Securinega leucopyus Sida sp. Strobilanthes sp. Viburnum sp. Viburnum sp. Volkameria fragrans Unidentified Shrubs Percentage of spp./plot
Rutaceae Verbenaceae
+
Verbenaceae Verbenaceae
+ +
P28
L3
w
L6
+ +
b
a
+ +
+
+ +
+
+
+ + + +
+
+ +
+
+
+ +
+
3 5
+
+
+ 7 10
+ + +
+
+ +
+ 2 3
+
+ +
+
5 17
d
+
+
+ +
Melastomaceae Rubiaceae Sambucaceae Euphorbiaceae Euphorbiaceae Malvaceae Acanthaceae Caprifoliaceae Caprifoliaceae Verbenaceae Acanthaceae
L12
+
+
Leg/Papillionideae Rutaceae Theaceae Moraceae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Sterculiaceae Iteaceae Malvaceae Leeaceae Leeaceae Melastomaceae
Number equals years of abandonment. w, wind; d, dehiscence; b, birds; a, all animals.
b
P21
Seed dispersal modeb
+
Allophyllus cobbe Allophyllus sootepensis Ardisia sp. Blumea balsamifera Boehmeria chiamaiensis Boehmeria sp. Boehmeria sp. Buddleja asiatica Cajanus cajan
a
P12
Abandoned Lisu fields
8 26
10 23
+ +
5 11
0
2
2
2
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
Table 4 List of vascular climber plant (inc. woody climbers, vines) and seed dispersal mode Climber species
Family
P. kesiya plantationa P7
Acacia comosa Acacia megaladena Argyreia sp. Argyreia speciosa ( = nervosa) Asparagus filicifolia Clematis smilacifolia Connarus sp., prob. semidecadendrus Dalbergia foliacea Dalbergia volubilis Derris sp. Derris sp. Dioscorea alata Dioscorea pentaphylla Diploclisia glaucescens Embelia ribes Embelia stricta Heterosmilax sp. Jasminum bifarium Maytenus marcanii Maytenus sp. Millettia extensa Mucuna pruriens Mussaenda sanderiana Paederia sp. Passiflora siamensis Piper sp. Pueraria sp. Rubus alceifolius Rubus sp. Shuteria sp. Shuteria sp. Smilax lanceifolia Smilax ovalifolia Smilax perfoliata Smilax sp. Smilax sp. Spatholobus compar Spatholobus sp. Tetrastigma sp. Thunbergia grandiflora Urena lobata Unidentified Unidentified Unidentified Climbers Percentage of spp./plot
P21
P28
Seed dispersal modeb
L3
w
d
b
a
0
0
0
0
+
Leg/Mimosoideae Leg/Mimosoideae Convolvulaceae Convolvulaceae
+
L6
+
+
+
+ +
+
+
+
+ +
+ + + + +
+
+
5 17
+ +
7 10
+ +
+
+ + + +
+
+ + 12 17
+
+
+
+
+ +
+
+ +
+
+ + +
+
+
+
+
+ +
+ +
L12
+
+
Liliaceae Ranunculaceae Connaraceae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Leg/Papillionideae Dioscoreaceae Dioscoreaceae Menispermaceae Myrsinaceae Myrsinaceae Smilacaceae Oleaceae Celastraceae Celastraceae Leg/Papillionideae Leg/Papillionideae Rubiaceae Rubiaceae Passifloraceae Piperaceae Leg/Papillionideae Rosaceae Rosaceae Leg/Papillionideae Leg/Papillionideae Smilacaceae Smilacaceae Smilagaceae Smilacaceae Smilagaceae Leg/Papillionideae Leg/Papillionideae Vitaceae Thunbergiaceae Malvaceae Leguminosae Leguminosae Leguminosae
P12
Abandoned Lisu fields
7 11
9 29
5 11
9 20
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U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183 Table 5 List of vascular herbs (inc. ferns), grasses and unidentified species and seed dispersal mode Family
P. kesiya plantationa P7
Herbs (incl. ferns) Alpinia (Zingiber) zerumbet Alpinia bracteata Alpinia sp. Alpinia sp. Artemesia dubia Artemesia roxburghiana Compositae sp. Costus laeta Crotalaria sp. Curculigo recurvata ( = Molineria capitulata) Curculigo sp. prob. latifolia Eupatorium (Ageratina) adenophorum Eupatorium (Chromolaena) odoratum Gerbera perperasum Polygonum chinense Pteridium aquilinum var. wightianum Scleria perpurascens Thelypteris sp. Unidentified Vernonia cinerea Vernonia sp. Herbs Percentage of spp./plot Grasses Imperata cylindrica Microstegium vagans Neyraudia reynaudiana Panicum montanum Panicum sp. Setaria glauca Setaria palmifolia Thysanolaena latifolia Unidentified Unidentified Grasses Percentage of spp./plot Unidentified species Unidentified Unidentified Unidentified Percentage of spp./plot
Zingiberaceae
P12
+
P21
+
Hypoxidaceae
+
w
d
b
a
0
0
0
0
+
+
L6
+
+
+
+
+ + +
4 13
+ +
+ +
+
+ +
+
6 9
+
+
3 10
+ + +
+
+
1 1
2 3
+
+
+
+
+
+ +
+
8 11
+
+
+ 4 6
+ + + + + 5 8
0 0
0 0
0 0
+
6 19
+ 5 11
5 11
+
+
+
+ + +
+ + +
4 13
3 7
2 4
0
0
0
0
0 0
+ + 2 5
0 0
0
0
0
0
Unidentified Unidentified 0 0
L12
+
+
Cyperaceae Thelypteridaceae Unidentified Compositae Compositae
Poaceae Gramineae Gramineae Gramineae Gramineae Gramineae Gramineae Gramineae Graminae Graminae
L3
+
Compositae Compositae Polygonaceae Dennstaedtiaceae
Seed dispersal modeb
+
Zingiberaceae Zingiberaceae Zingiberaceae Compositae Compositae Compositae Costaceae Leg/Papillionideae Hypoxidaceae
Compositae
P28
Abandoned Lisu fields
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Table 5 continued
Family
Total number of species (Tables 2–5) a
P. kesiya plantationa
Abandoned Lisu fields
Seed dispersal modeb w
P7
P12
P21
P28
L3
L6
L12
30
67
72
65
31
44
45
d
b
a
Number equals years of abandonment. w, wind; d, dehiscence; b, birds; a, all animals.
b
tively light. No pine regeneration was observed, whereas other trees had regenerated well and were regularly distributed throughout the plot. A small number of native seed trees were left at the top of the ridge outside of the plot. Stump regeneration and coppicing were observed more frequently than in all other plots. In the 21-year-old plantation some pine mortality was noted. Many tree seedlings were recorded in a ground cover dominated by E. adenophorum. The middle canopy was almost absent. Many climbers were recorded. There were no seed trees left in or outside the plot. Coppicing and stump regeneration was not obvious. The 28-year-old plantation stand was dominated by P. kesiya, but was structurally rich in species, canopy layers and tree sizes. A relatively high number of standing pines had died very recently of uncertain causes. Ground cover was light. There were no old seed trees left in or surrounding the plot. Very few species were observed growing from old stumps or were coppicing. The 3- and 6-year-old abandoned Lisu fields more closely resembled grassland than secondary forest, with scattered shrubs and trees. The succession in the 12-year-old Lisu abandoned field showed rather scattered trees with small crowns, the ground being covered with Imperata cylindrica grass. The stem basal area of P. kesiya and of tree species combined increased with age from the 7- to the 21year-old stands and declined in the 28-year-old plot, due perhaps to the extraction of approximately 40% of the pines in this plot at the age of 20. The stem basal area of other trees in the plantation plots varied between 1.88 and 7.75 m2/ha, with a peak in the 12year-old plot. In the abandoned Lisu field plots the stem basal area increased from 0 to 7.94 m2/ha from the 3-year-old to the 12-year-old plot (Fig. 1). For the stem basal area, the Bitterlich variable radius method
measurement of larger samples gives an indication of how plot data represents a whole stand (Kramer and Akc¸a, 1982). The 7-, 21- and 28-year-old plantation plots seemed to show statistically correct results, as the ratio of plot data to Bitterlich data was below 10%. For the 12-year-old plantation the stem basal area of pines and of other trees collected as plot data was not similar enough to the Bitterlich measurements to allow this plot to be representative of the whole 12-year-old stand. In fact, the Bitterlich data showed that the 12year-old plantation plot data overestimated the stem basal area of other trees, but underestimated the stem basal area of pines. However, Fig. 1 shows the Bitterlich measurements of the stem basal area at dbh for the pine plantation plots and the abandoned Lisu fields. The ratio of pines to other tree species is an indication of the degree of stand dominance by non-pine species. Fig. 2 shows the number of trees per ha for the plantation plots of different ages and for the abandoned Lisu fields plots. The density of P. kesiya declined with increasing age of the pine stands whereas the density of all other tree species increased with time, both in the plantations and the abandoned Lisu fields. The 12-year-old plantation was almost five times higher in density of tree individuals than the non-planted one. 3.2. Species composition and diversity The number of trees andthe number of tree species was low in the 7-year-old plantation plot (13 tree spp.) and in all abandoned Lisu field plots (4–24 tree spp.), but almost equally high in the 12-, 21- and the 28-year-old plantation plots (41–47 tree spp.), respectively, showing the highest numbers (47 tree spp.) in the 12-year-old plantation plot (Tables 2, 3, 4 and 5). Most tree species common in the 12-, 21- and 28-year-old plantation plots, such as Alstonia glaucescens, Berrya mollis, Engel-
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183 Table 6 Sørensen’s index of similarity (ISs) for all vascular plant species in P. kesiya plantations and in natural succession plots in abandoned Lisu fields P21 P12 P7 L12 L6 L3
35 35 19 18 13 13 P28
35 23 14 9 6 P21
22 18 18 10 P12
13 14 33 P7
22 18 L12
24 L6
P, P. kesiya plantation; L, natural succession in abandoned Lisu fields; numbers indicate years after afforestation/length of abandonment.
hardia spicata, Eugenia cumini, Ficus hirta, Gluta, Michelia baillonii, Phyllanthus emblica and Schima wallichii, have mostly pioneer characteristics, but are components of the potential forest types at that elevation and soil condition. These tree species are widely distributed in the survey area. Most of these species were lacking in the abandoned Lisu fields. Fagaceae species, mainly Castanopsis and Lithocarpus species,were once common in the different types of oak forests of the region. Six Fagaceae species were recorded in the 12year-old plantation plot, three and two in the 21- and 28year-old plots, respectively, and none in all other plots. Climber species were rarely common to two or more plots. Eupatorium adenophorum, a herb, was found in every plot. Most grass species (five) were recorded in the 28-year-old plantation. Four grass species were found in the 6-year-old abandoned Lisu fields and three grass species were found in both the 7-year-old plantation and the 3-year-old abandoned Lisu fields. Grass species made up 13% of all species in this plot, indicating a grass dominated area. A list of all species, categorized by life form, is presented in Tables 2–5. Sørensen’s index of similarity (ISs) values ranged from 6 to 35 among plots. The ISs values comparing the plantation plots with the abandoned Lisu fields were very low (6–18), except for the 3-year-old abandoned Lisu field compared to the 7-year-old plantation (ISs = 33). Intermediate ISs values of 35 were found for comparisons of the 12-, 21- and 28-yearold plantation plots. Comparisons among the Lisu fields also showed relatively low ISs values, indicating a low degree of similarity in species composition among them (Table 6). Species composition was also investigated through
181
a complementarity check. In seven plots totalling 1.12 ha, the fraction of locally available species found still seems small, as the cumulative number of species was still increasing from 197 species in the sixth plot to 216 species in the seventh plot (Fig. 3). In other words, 19 out of 45 species (42%) in the 12-yearold abandoned Lisu field were not surveyed previously. Newly listed species declined slowly from 58 to 38, 28, 23, 23 and finally 19 (Fig. 3). With 216 species of vascular plants and 112 tree species recorded in seven plots covering 1.12 ha, species diversity is apparently quite high in the survey area. 3.3. Seed dispersal Old seed trees growing in the plantations were rare in the vicinity of the stands studied. The majority of tree species, 55 out of 104, were dispersed by animals of all kinds. Thirty-six out of these 55 tree species were dispersed by birds. Seed dispersal characteristics were not obtained for 14 tree species. Animal dispersed tree species were more frequent in the plantation plots. In the 3-, 6- and 12-year-old abandoned Lisu fields 50, 42 and 46%, respectively, were dispersed by animals. In the 7-, 12-, 21- and 28-yearold plantations 46, 57, 56 and 51%, respectively, were dispersed by animals. Most tree species of the potential lower montane oak and pine-oak forests (e.g. Fagaceae and some Myrsinaceae and Moraceae spp.) are dispersed by animals. These trees were almost exclusively found in the 12-, 21- and 28-
Fig. 3. Complementarity of vascular plant species in 7-, 12-, 21and 28-year-old P. kesiya plantation plots and in 3-, 6- and 12-yearold abandoned Lisu fields. The plot size is 1600 m2 for all plots.
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Table 7 Number of tree species according to seed dispersal mode in P. kesiya plantations and in natural succession plots in abandoned Lisu fields
P7 P12 P21 P28 L3 L6 L12 Total no. of tree species
Wind
Dehiscence
Birds only
All animals
No. tree spp.
5 10 11 13 1 5 10 25
3 9 5 13 1 3 5 22
4 14 17 16 1 6 9 36
6 27 23 22 2 8 11 55
13 47 41 45 4 19 24 112a
P, Pinus kesiya plantation; L, natural succession in Lisu abandoned fields; numbers indicate years after afforestation/length of abandonment. a Manner of seed dispersal not identified for 14 species.
year-old plantation plots, while relatively few were found in the 12-year-old abandoned Lisu fields (Table 7).
4. Discussion Twenty-eight years after plantation of P. kesiya on abandoned swidden plots a well structured forest had developed. The 12-year-old plantation site was much better developed with respect to structure and species diversity than the abandoned Lisu agricultural site of the same age. The stem basal area was almost twice as high. Species composition of the 12-year-old plantation plot seemed to be closer to the potential forest type than the 12-year-old abandoned Lisu fields. It appears that the declining stem basal area of P. kesiya trees from the 21-year-old plantation to the 28year-old plantation was replaced by the stem basal area of other tree species. Secondary diseases seemed to be of no importance in pine afforestations until the age of 20. After that, dying pines may even contribute to enhanced natural succession by creating gaps, similar to the logging operations in the 28-year-old plot which had reduced the stem basal area. Many of the tree species found in the plots were in fact tree seedlings or very small saplings which may or may not survive this stage. All plots showed a rather sharp decline in the number of individuals
and species with higher dbh, prolonged in the 28year-old plantation plot. It seemed as if other trees couldn’t survive at a sufficient rate as the plantations grew older. This suggests that creating gaps of various sizes, as was done in the 28-year-old plot, eventually leads to better structured stands. Koop and Siebel (1993) have already tried various conversion management measures in temperate forest plantations with promising results. It would be useful to apply and monitor different silvicultural treatments in tropical environments to validate this hypothesis. The cutting of pines might then not only benefit the regeneration process, but also generate economic benefits. Eupatorium adenophorum, E. odoratum, Polygonum chinense and Pteridium aquilinum were found in most plots, indicating severe disturbances of the survey sites. The number of vascular plant species and the number of tree species in the plantation plots was much higher than in the succession on abandoned Lisu fields, indicating that reforestation of severely disturbed areas with P. kesiya might indeed speed up the successional process and allow new species to thrive. It was shown that the fraction of species found in seven plots (total area of 1.12 ha) is far from complete for the area surveyed. The overall number of tree species found (112) is very high, indicating an area of high diversity (Elliott et al., 1989). The study revealed that birds and other animals contribute to forest regeneration as seed dispersers. Parrotta (1993) has observed a significant negative correlation between seedling density and distance to the nearest possible seed source. However, as seed trees were scarce in the vicinity of the plots, animals must have carried the seeds from far away. Ewel (1983) has stated that the high net productivity of successional ecosystems supports large animal populations. This suggests that an important role of pine plantations in the natural regeneration process induces habitat as well as plant composition interactions. Feeding, breeding and roosting visits alone provide opportunities for seed dispersal. Two possible ways of enhancing regeneration are proposed, i.e. effective wildlife protection and habitat development such as the planting of species attractive to animals to lure them into the plantation. The regeneration process of forests is always subject to disturbances. It is important to know which
U. Oberhauser / Forestry Ecology and Management 99 (1997) 171–183
disturbances prevail in a given surrounding to protect the regeneration from damage. For the study site the development of new agricultural methods is a permanent threat, which could be addressed by participatory land use planning methods (Limchoowong and Oberhauser, 1996). It is nowadays widely accepted that uncontrolled fires as another widespread disturbance cause severe damage to the highland ecosystem, although not all interrelations are yet fully understood (Elliott et al., 1989). One important aspect is that once a previously damaged area burns the successional development starts again at a very early stage. Any restoration through plantation has to take these disturbances and the social and cultural implications into account. Acknowledgements This study was conducted during a 3-year term of development assistance by the German Development Service (DED) to the Thai-UN Sam Muen – Highland Development Project. The author wishes to express his gratitude to Mr Samer Limchoowong, former director of the Thai-UN Sam Muen – Highland Development Project. He supported this study from its initiation until the end. The author also wishes to thank the late Dr Tem Smitinand, retired director of the Royal Forest Departments’ herbarium, for his field plant identification. Dr James F. Maxwell provided invaluable help in identifying seed dispersal mechanisms and cross-checking species. The staff of Watershed Development Unit Khun Khong and of the Sam Muen Project, Royal Forest Department, were extremely helpful in providing facilities and support for the study. Many thanks to Mr Bradford Withrow-Robinson for his critical comments and editing of the manuscript. References Elliott, S., Maxwell, J.F. and Beaver, O.P., 1989. A transect survey of monsoon forest in Doi Suthep-Pui National Park. Nat. Hist. Bull. Siam Soc., 37: 137–171.
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Ewel, J., 1983. Succession. In: F.B. Golley (Editor), Tropical Rain Forest Ecosystems, A. Structure and Function. Elsevier, Amsterdam, pp. 217–223. Kanjunt, C. and Oberhauser, U., 1996. Successional forest development in abandoned swidden plots of Lisu, Hmong and Karen ethnic groups (in Thai – English version available through authors). In: B. Boontawee (Editor), Supplementary Papers of the National Forestry Conference 1995 A century of Forestry in Thailand. RFD, Bangkok, pp. 129–133. Kijkar, S., 1987. Pines in Thailand. Silviculture Branch. RFD, Bangkok (in Thai). Koop, H. and Siebel, H.N., 1993. Conversion management towards more natural forests: evaluation and recommendations. In: M.E.A. Broekmeyer, W. Vos and H. Koop (Editors), European Forest Reserves. Pudoc, Wageningen, pp. 199–201. Koskela, J., Kuusipalo, J. and Sirikul, W., 1995. Natural regeneration dynamics of Pinus merkusii in northern Thailand. For. Ecol. Manage., 77: 169–179. Kramer, H. and Akc¸a, A., 1982. Leitfaden fuer Dendrometrie und Bestandesinventur. J.D. Sauerla¨nder’s Verlag, Frankfurt am Main, 251 pp. (in German). Limchoowong, S. and Oberhauser, U., 1996. Can villagers manage the highland resources. In: F. Turkelboom, K. Van Look-Rothschild and K. Van Keer (Editors), Highland Farming: Soil and the Future, pp. 16–18, Soil Fertility Conservation Project, Maejo University Thailand – Catholic University of Leuven, Belgium, pp. 13–22. Mueller-Dombois, D. and Ellenberg, H., 1974. Aims and Methods of Vegetation Ecology. Wiley, New York, 547 pp. Parrotta, J.A., 1993. Secondary forest regeneration on degraded tropical lands: the role of plantations as ‘foster ecosystems’. In: H. Lieth and M. Lohmann (Editors), Restoration of Tropical Ecosystems. Kluwer, Dordrecht, pp. 63–73. Phugjaroon, W. and Kaewamphut, T., 1993. Structure of a Hill Evergreen Forest at Watershed Development Unit 26, Chiang Mai Province. Research Section, Watershed Management Division, RFD, Bangkok, 41 pp. (in Thai with English abstract). Pielou, E.C., 1995. Biodiversity versus old-style diversity: measuring biodiversity for conservation. In: T.J.B. Boyle and B. Boontawee, (Editors), Measuring and Monitoring Biodiversity in Tropical and Temperate Forests. CIFOR, Bogor, pp. 5–17. RFD, 1993. Statistics of Forest in Thailand. Planning division, RFD, Bangkok. Santisuk, T., 1988. An account of the vegetation of northern Thailand. Geoecological Research 5, Franz Steiner Verlag Wiesbaden GmbH, Stuttgart, 103 pp. Werner, W.L., 1996. Pinus in Thailand. Geoecological Research 7, Franz Steiner Verlag Wiesbaden GmbH, Stuttgart, 287 pp. (in German).