Pongsak Sahunalu

Habitat differentiation of Lauraceae species in a tropical lower montane forest in northern Thailand

Dependency on topographical habitat was examined for Lauraceae tree species in a lower montane forest using a large-scale research plot established at Doi Inthanon National Park, northern Thailand. Twenty species of 10 genera of Lauraceae were recorded in a 7.5-ha part of the plot; Lauraceae accounted for 18% of the total basal area. Lauraceae was the most species-rich and most abundant family in the plot. In a cluster analysis based on the matrix of spatial associations between species, two clusters were recognized. Members of one cluster seemed to associate with lower-elevation habitats, and members of the other associated with habitats on ridges. By subdividing the study plot into 20 m × 20 m squares, a discriminant analysis could be applied to the presence–absence data for the 17 species that had sufficient population density. The predictor variables used were the relative elevation, slope inclination, slope direction (transformed to deviation from SSW) and slope convexity for each of the squares. The discriminant models were tested statistically by applying the random shift technique. The models were significant for 11 of the species (65% of the species examined) and were associated with the topographical condition of the habitat. Stepwise selection of the predictor variables for these 11 species revealed that relative elevation and slope convexity were the most important factors for predicting the presence or absence of the Lauraceae species. Both these variables were considered to indicate the hydrological condition of the habitat.

Soil carbon/nitrogen ratio as a site quality index for some South-east Asian forests

The carbon-nitrogen (C/N) ratio of soil organic matter is related to the patterns of nitrogen immobilization and mineralization during organic matter decomposition by micro-organisms (Swift et al. 1979). Its value decreases as decomposition proceeds (Swift et al. 1979), is negatively correlated with the rate of nitrogen mineralization in decomposition experiments by soil incubation (Tsutsumi 1987a), and can indicate the decomposition rate in terrestrial ecosystems (Jordan 1985). The studies of soil carbon and nitrogen in tropical forest ecosystems (Jordan 1985), such as lowland rain forests (Uhl & Jordan 1984, Yoda & Kira 1982), seasonal forests (Hase & Folster 1982), and montane rain forests (Edwards 1982, Edwards & Grubb 1982), and various types of forests along altitudinal gradients (Marrs et al. 1988, Yoda & Kira 1969), have suggested an increase of the soil C/N ratio with a decrease in temperature and an increase in moisture (Jenny 1941). However, it also depends on the nitrogen contents of the litter itself (Jordan 1985, Swift et al. 1979), local variations in soil conditions according to topography and parent material (Tsutsumi 1987b). In an analysis of the structure and environmental relationships of seven tropical forest stands, Jordan (1985) found that the first principal component, which accounted for 63% of the ecosystem variance, was highly correlated (r = 0.94) with total soil nitrogen. Nitrogen has great effect on plant growth, affecting cell number and cell size (Chapin 1980). The availability of soil nitrogen to plants is determined largely by its mineralization during the decomposition of organic matter (Jordan 1985, Swift et al. 1979). Therefore we may expect a relationship between the C/N ratio and tree growth. This was

Habitat divergence in sympatric Fagaceae tree species of a tropical montane forest in northern Thailand

Spatial distributions of many tropical trees are skewed to specific habitats, i.e. habitat specialization. However, habitats of specialist species must be divergent, i.e. habitat divergence, to coexist in a local community. When a pair of species specialize in the same habitat, i.e. habitat convergence, they could not coexist by way of habitat specialization. Thus, analyses of habitat divergence, in addition to habitat specialization, are necessary to discuss coexistence mechanisms ofsympatric species. In this study, the habitat specialization and habitat divergence along topographic gradients of eight sympatric tree species of the Fagaceae were studied in a 15-ha study plot in a tropical lower montane forest in northern Thailand. A statistical test with torus shift randomizations for 9 6 73 trees of Fagaceae revealed significantly biased distributions for all of the species, for at least one of the four topographic variables used: elevation, slope inclination, aspect and convexity. Slope convexity was the most critical topographic variable, along which all but one species had significantly skewed distributions. Out of 112 possible combinations of species pairs and topographic variables, 18 (16%) and two pairs (1.8%) showed significant habitat divergence and habitat convergence, respectively. The observed habitat divergence alone could not completely explain the coexistence of the eight species. There was a gradation in the habitat position of each species, with relatively large overlaps between species distributed in similar habitats, and small overlaps between species associated with contrasting habitats, respectively. The gradual changes in the habitats of the species suggested that dividing the species into a small number of distinct habitat groups, such as ridge and valley specialists, would not be straightforward.

Intra- and interspecific variation in wood density and fine-scale spatial distribution of stand-level wood density in a northern Thai tropical montane forest.

Tropicaltreewooddensityisoftenrelatedtootherspecies-specificfunctionaltraits,e.g.size,growthrateand mortality. We would therefore expect significant associations within tropical forests between the spatial distributions of stand-level wood density and micro-environments when interspecific variation in wood density is larger than intraspecific variation and when habitat-based species assembly is important in the forest. In this study, we used wood cores collected from 515 trees of 72 species in a 15-ha plot in northern Thailand to analyse intra- and interspecific variationinwooddensityandthespatialassociationofstand-levelwooddensity.Intraspecificvariationwaslowerthan interspecific variation (20% vs. 80% of the total variation), indicating that species-specific differences in wood density, rather than phenotypic plasticity, are the major source of variation in wood density at the study site. Wood density of individual species was significantly negatively related to maximum diameter, growth rate of sapling diameter and mortalityofsaplings.Stand-levelmeanwooddensitywassignificantlynegativelyrelatedtoelevation,slopeconvexity, saplinggrowthrateandsaplingmortality,andpositivelyrelatedtoslopeinclination.East-facingslopeshadsignificantly lower stand-level mean wood densities than west-facing slopes. We hypothesized that ridges and east-facing slopes in the study forest experience strong and frequent wind disturbance, and that this severe impact may lead to faster stand turnover, creating conditions that favour fast-growing species with low wood density.

Semiquantitative color profiling of soils over a land degradation gradient in Sakaerat, Thailand.

In this study, we attempted multivariate color profiling of soils over a land degradation gradient represented by dry evergreen forest (original vegetation), dry deciduous forest (moderately disturbed by fire), and bare ground (severely degraded) in Sakaerat, Thailand. The soils were sampled in a dry-to-wet seasonal transition. Values of the red–green–blue (RGB), cyan–magenta–yellow–key black (CMYK), L*a*b*, and hue–intensity–saturation (HIS) color models were determined using the digital software Adobe PhotoshopTM. Land degradation produced significant variations (p < 0.05) in R, C, Y, L*, a*, b*, S, and I values (p < 0.05). The seasonal transition produced significant variations (p < 0.05) in R, G, B, C, M, K, L*, b*, and I values. In discriminating the soils, the color models did not differ in discriminatory power, while discriminatory power was affected by seasonal changes. Most color variation patterns had nonlinear relationships with the intensity of the land degradation gradient, due to effects of fire that darkened the deciduous forest soil, masking the nature of the soil as the intermediate between the evergreen forest and the bare ground soils. Taking these findings into account, the utilization of color profiling of soils in land conservation and rehabilitation is discussed.

Density effects and self-thinning in even-aged pure stands ofEucalyptus camaldulensis Dehn

The competition density effect and changes of mean total tree weight (w) and stand density (ρ) during course of self-thinning were examined in even-aged pure stands ofEucalyptus camaldulensis Dehn. which were planted in the tropical monsoon region. The level of competition was controlled by changing the initial stand density from 625 trees ha−1 to 40,000 trees ha−1. Hozumis model was used to describe thew-ρ trajectory with aging of each stand and thew-ρ relation between stands of different densities at each time. The higher density produced trees of smaller mean tree sizes. The higher the density, the sooner self-thinning began. The growth curve ofE. camaldulensis followed the logistic growth curve where both maximum size and intrinsic growth rate change with time. Mean intrinsic growth rate was maximized at initiation of growth after lag time and then gradually decreased as time progressed. Hozumis model was considered to be the best model with wide applicability for describing and comparing the growth characteristics during the course of self-thinning among different species, especially in tropical forest plantations, in which many diverse species were used for reforestation.

Combinations of trees and crops in the taungya method as applied in Thailand

In Thailand the taungya reforestation method has been practiced primarily in order to rehabilitate wasteland, particularly under the Forest Village Programme. While various combinations of trees and crops are found in the taungya method on a minor scale, the major combinations are teak with upland rice in the north, fast-growing trees with cassava in the northeast, fast-growing trees with maize in the west, and para-rubber or fast-growing trees with fruit trees in the south. These combinations relate to the differences in climatic conditions, mainly the duration of the rainy season.

Characteristics and management of tin mine tailings in Thailand

Summary Soil characteristics of tin mine tailings are generally low fertility and unfavourable physical conditions for supporting plant growth resulting from heavy disturbance during tin mining. Management of the tailings for further uses may be dependent upon the ownership of the tailing land. Attempts to utilize the tailings for agricultural use through experiments and trials have been made by the Tin Mine Spoil Research Station among others. These included forest tree planting, growing of agricultural crops and improvement of the soil by several methods to elevate the fertility status and create a more favourable condition for plant growth. Successful methods consist of chemical fertilizer either used directly or by mixing with manure and other materials that are likely to improve the physical properties of tailings and ameliorate toxic conditions. There is still not large-scale application of the research findings due to difficulties in initial improvement of the topographic condition of the tailings and the economic situation of the owner. Future studies on mine tailings aim at lowering the cost of reclamation by using locally available materials to improve both physical and chemical conditions through the recycling of organic wastes and to improve planting methods so as to gain more plant production.

A preliminary study of changes in forest stratification along environmental gradients in Southeast Asia

Changes in forest stratification along environmental gradients in Southeast Asian forests were studied, by applying Quantification Method I to the records of tree height inventories and environmental conditions in 29 study forest stands. To stratify individual trees into subpopulations in a stand, an empirical and graphical method was used. After stratifying all the component individuals of the stand into subpopulations, the number of subpopulations per stand and mean tree height per subpopulation were calculated and adopted as indices of forest stratification. Of the two indices, the latter index changed linearly with respect to the maximum tree height in the stand. Hence, the number of subpopulations and the maximum tree height as a substitute for mean tree height per subpopulation were biotic dependent variables in the application of Quantification Method I, while abiotic independent variables were the following six categorized environmental factors: the number of wet months with over 100 mm month−1 rainfall in a year, occurrence of fog, mean annual temperature, magnesium accumulation in mineral soil, soil water drainage, and forest fire. It was concluded that these biotic and abiotic variables were the components of multivariate regression models, which successfully explained the development of forest stratification in terms of habitat conditions.