The altitudinal gradient of vegetation of the Barisan range in a coastal region near Padang, West Sumatra, was studied in 10 plots (0.1-6.55 ha) distributed from 600 to 1780 m. Trees with a diameter at breast height of more than 10 cm were employed for classification of the vegetation. Four vegetation zones, two types of montane and two types of lowland vegetation, were recognized based on cluster analysis, floristic information, and the physiognomy of these forest stands. An upper zone of montane vegetation (Lower montane Fago-Myrtaceous forest) was distinguishable from a lower zone (Sub-montane Fago-Myrtaceous forest) due to the remarkable dominance of several species of Fagaceae and Myrtaceae, and its lower canopy height. The two zones of lowland vegetation (Upper hill dipterocarp forest and Mid-hill dipterocarp forest) were distinguishable by their species composition of Dipterocarpaceae and stratification of the stand. The altitudinal zonation corresponded well with classic zonation patterns previously reported for West Malesia, but the critical threshold altitudes were lower in comparison with those in other regions. The borderline between the lowland and montane vegetation, corresponding to a Kira’s warmth index of WI = 180 °C · month, was around 200 m lower in Padang than in other regions of West Malesia, and the critical altitude between the two zones of lowland vegetation was also around 300 m lower in Padang than on Mt. Kinabalu. The characteristics of altitudinal zonation in Padang were discussed with reference to the climatic features of this region, namely, the low temperature and hyperhumidity.

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The altitudinal distribution of Fagaceae in West Sumatra was studied on the basis of herbarium specimens and field tree censuses conducted at Gunung Gadut and Sipisang. Forty-two species were examined (Castanopsis: 8 spp., Quercus: 8 spp., Lithocarpus: 25 spp., and Trigonobalanus verticillata), and it was revealed that altitudinal distribution patterns vary among species and genera. The species richness of Fagaceae in West Sumatra was highest at 400-700 m, decreasing with increasing altitude above 700 m, while about half the total number of species occurred below 400 m. Though the altitudinal distribution patterns of some species were compressed toward a lower altitude in Gunung Gadut, species richness in Gunung Gadut and Sipisang regions were also highest at 400-700 m above sea level (76 % of 33 species were found growing in these regions), and more than half of the species were found at 150-400 m. Quercus showed gradual replacement/overlapping of higher/lower altitudinal species at a range of 700-1100 m, and Lithocarpus showed a remarkably high species richness at 400-700 m in both regions. The altitudinal diversity patterns of Fagaceae appeared to involve both species coexistence/concentration at particular altitudes and species replacement with changing altitudes. The high species richness of Fagaceae at 400-700 m was especially due to the coexistence and concentration of Lithocarpus species.

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The floristic composition of a tropical hill forest in Ulu Gadut, West Sumatra, Indonesia, was studied. High species diversity and differences in the floristic composition compared to other forests in West Malesia were observed. Based on the tree numbers of common species in 20 × 20m quadrats, habitat axes representing floristic composition were determined by detrended correspondence analysis. Axis 1 was significantly related to the slope convexity and stand height of a quadrat, indicating that the floristic composition is influenced not only by topography but also by growth stage and disturbance. The major disturbance in this forest prior to the study was local logging, the influence of which was found not only in the variation in floristic composition but also in vegetation development after disturbance. We concluded that the harvest of upper layer trees by local loggers enhanced the growth of lower layer tree species in this forest. The estimated original vegetation without logging differed from that of other forest stands in West Malesia because of its relatively low dominance of Dipterocarpaceae and high dominance of Fagaceae. This might have been caused by the lower temperature of the plot compared with other forests at similar altitudes in West Malesia regions. This climatic feature is also thought to contribute to the high diversity of the plot.

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This study aimed to clarify the impacts of recent dry weather on the stand dynamics of a tropical rainforest in Sumatra based on long-term observations of a 1-ha plot from 1981 to 2004 at approximately 1.5-year intervals. The west coastal area of Sumatra has suffered severe dry weather during the last decade due to Indian Ocean Dipole Mode events; droughts in 1994 and 1997 were particularly severe. During the study period, the basal area of the plot increased linearly over the first 10 years then tended to remain constant for the last 10 years. We assessed the influences of dry weather on this growth pattern by comparing growth traits of trees (growth, mortality and recruitment rates) among three periods of differing dry weather intensity, being 1981-1989, 1994-1999 and 1999-2004. These traits clearly changed among the three periods, and as a result we could assess the impacts of dry weather from their temporal correspondences. The major 24 genera in the study plot largely changed their basal area dominance during the 22 years. Soft wood genera (broad leaved trees) with higher growth rates increased and hard wood genera with lower growth rates decreased. These changes were caused by increased competition among trees due to the death and defoliation of many canopy trees under the severe water stress conditions. Increased numbers of soft wood genera means that the total biomass will decrease under these basal area conditions because of their low bulk density of woody organs and lower maximum height. This study suggests that the impacts of dry weather in this region might extend to montane forests in the cloud belt.

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Human impacts on a tropical rain forest were observed through stand structure and dynamics of a rural forest in Sumatra. Species composition has been successively changing through continuous and biased impact by local people under nearly dynamic equilibrium conditions in tree density and basal area. Soft wood species (broad-leaved trees with low stem hardness) with fast growth-rates tended to increase their dominance under higher human impact. Because of the lower bulk density of their stem wood and lower tree height, the stem biomass in a rural forest stand could be estimated at only a half of that of a mature forest even under the same basal area conditions. Turnover times of basal area in these rural forests were about 15 years and 25 years for open forest stands and closed forest stands, respectively. When we examined the productivity of several rural forest stands in the study area, an optimum curve could be drawn for the relationship between biomass and productivity. We propose a new criterion for the management of secondary forests based on their economical and environmental functions.

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Leaf longevity of tropical shrub species was examined with reference to the intensity of disturbance. Species with lower stem hardness likely prioritize a higher volume of growth at early growth stages over the physical strength of the stem. This trait is thought to be advantageous for species suffering frequent disturbance, thus it is believed that stem hardness could be used as a measure of adaptability to disturbance. The weight ratio of leaves to stalks on a twig is an important parameter to assess the leaf longevity satisfying the minimum maintenance costs of a twig. In this study, the leaf longevity of shrubs was shown to be reciprocally related to the weight ratio. Based on this relationship, it was revealed that these species gain suitable leaf longevity by regulating this weight ratio under conditions of the minimum maintenance. A positive correlation between leaf longevity and stem hardness was also observed among shrub species. Assessment of the niche of these species in a secondary sere according to stem hardness verified that leaf longevity increases with progressing succession as a result of regulation of the weight ratio.

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The aggressive reproduction strategy of the naturalized shrub Piper aduncum L., introduced from humid Neotropical regions, was studied in Sumatra paying special attention to fruit production and leaf longevity. A single piper shrub produced inflorescences throughout the year and the annual production of a mature inflorescence was estimated at 7.8 ton ha^-1 yr^-1. It was also shown to consume 100 kg of nitrogen per hectare for annual fruit production on the basis of its crown projection area, while 60 % of nitrogen in leaves and branches was reabsorbed with senescence and death. Average leaf longevity was 158 ± 48 days with an average turnover rate of 2.5 ± 0.51 yr^-1. This high turnover rate is considered advantageous for continuous fruit production from early growth stages through effective allocation and reabsorption of energy and nutrients. Next, a mathematical model for optimum leaf longevity was proposed taking into account the maintenance costs of a single branch. The model showed that the observed leaf longevity approximately satisfied the expected minimum maintenance cost of a mature branch. A short leaf life span could save stem and branch construction costs through effective leaf production with low biomass. Economical branch structures in terms of energy and nutrient use could allow allocation of more resources to fruit production. This prioritization of fruit production over construction of a durable stem and branches could be evaluated as an adaptive living strategy of this shrubby pioneer species. Based on the proposed model, the adaptive survival strategies of other species were discussed with special reference to the relationship between leaf longevity and branch structure.

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We examined the variation in forest structure, species diversity and floristic composition of trees for different minimum sizes (≥ 4.8 cm and ≥ 10 cm stem diameter) in six 0.25-ha plots of a tropical montane forest (1600 m above sea level) on Mount Kinabalu, Sabah, Malaysia. Four plots are parts of a 2.74-ha plot, and two are located 75 m and 200 m apart from the others. In all, the six plots are distributed in an area of approximately 8 ha (450 m × 175 m) on similar topography (sideslopes). Forest structure (e.g. stem density, basal area and estimated aboveground biomass) appeared to be similar among the six plots. Tree species richness per plot varied little (91-102 for stems ≥ 4.8 cm diameter and 60-72 for stems ≥ 10 cm diameter). Several indices of species diversity (or evenness) were also within narrow ranges, correlated with species richness. The dominance of species varied greatly among the six plots, but that of genus and family was relatively consistent. Analysis based on the 2.74-ha plot suggested that this reflected different habitat associations with microtopography among congeneric or confamilial species and intraspecific aggregation. Similarity indices based on presence/absence of species (e.g. Jaccard and S.rensen indices) were negatively correlated with spatial distances between plots (for stems ≥ 4.8 cm diameter), but those based on relative abundance of species were not. Indices of species diversity (or evenness) and similarity based on basal area were correlated between two minimum sizes (≥ 4.8 cm and ≥ 10 cm diameter), but those based on number of stem or presence/absence of species were not. We concluded that variations in forest structure, tree species diversity and floristic composition at genus and family levels were small at this spatial scale, and that the results obtained in any single 0.25-ha plot can be reasonably extrapolated to the other stands on similar topography in this area except dominance of species.

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