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This study was conducted in the alluvial forest and heath forest in the lowland tropical forest of Sepilok Forest Reserve, Sabah, Malaysia. The main objective was to assess how forest structure regulates rainfall partitioning in both forests. Field monitoring involved a series of forest inventory work to determine the forest stand characteristics. Mann Whitney U test was performed to compare physical characteristics between the two forests. Meanwhile rainfall partitioning was quantified by measuring the throughfall (Tf) for a period of 12 months in ten (15 x 15 m) Tf plots and a simple linear regression was conducted to obtain a regression model to estimate Tf. In terms of stand structure characteristics, data in the alluvial forest indicates wider variation. Percentage of Tf as of gross rainfall (Pg) is higher in the heath forest than in alluvial forest with the value of 89.5 % and 76.8 %, respectively. Representative trees were selected for stemflow (Sf) estimation at each forest type. The estimated Sf is 0.2 % in alluvial forest and 0.5 % in heath forest. In this study, tree diameter at breast height (Dbh) and height as well as aboveground biomass were identified to have some influence in Tf and Sf production. Keywords: rainfall partitioning; gross rainfall; throughfall; stemflow; Mann Whitney U; simple linear regression

Trade-offs in wood anatomical characteristics reflect different strategies used by trees to deal with water transport in response to variation in environmental conditions. To study vascular strategies for Bornean rainforest trees, we compared water transport-related anatomical characteristics in branch wood between the common tree species Vatica dulitensis (Dipterocarpaceae) from old-growth forest and the common pioneer tree species Macaranga gigantea (Euphorbiaceae) from selectively logged forest. We hypothesised that the vessel traits of the pioneer species would reflect the need to capture and transport resources to support its fast growth rate (resource-acquisitive strategy), while the species of the old-growth forest would display more conservative vessel traits (resource-conservative strategy). We found that M. gigantea had significantly greater vessel area, hydraulically weighted diameter, vessel area to number ratio, and potential hydraulic conductivity than V. dulitensis. These results suggest that vessel traits of the common old-growth species would ensure high hydraulic safety during occasional drought when soil moisture is limited, while the common species of selectively logged forest possesses an efficient water transport system but its vessels would confer lower hydraulic safety during drought conditions. These contrasting vascular strategies highlight the potential for divergent responses of species of Bornean forest trees to future climatic extremes.

We measured the terminal velocity of helicopter-like fruit from the Dipterocarpaceae family and present a model predicting the terminal velocities for all dipterocarp species in the Malesiana region. A ballistic model of seed dispersal using the observed terminal velocities predicted dispersal distances of 17–77 m under normal atmospheric conditions. These data are of applied use in parametizing models of species coexistence, forest regeneration and habitat connectivity in Southeast Asian tropical forests. Abstrak Kami telah melakukan pengiraan untuk menguji halaju terminal (terminal velocity) pada buah dari keluarga Dipterocarpaceae di Malaysia dan membentangan kertas kerja ini bagi tujuan untuk menunjukkan keputusan yang telah diperolehi. Dengan menggunakan Model Ballistik, penyebaran biji melalui pemerhatian halaju terminal (terminal velocitiy), penyebaran biji mampu dilakukan pada jarak 17m hingga 77m dalam keadaan cuaca yang normal. Data-data yang dihasilkan dari penelitian ini dapat digunakan untuk menguji “species coexistence”, pertumbuhan semula hutan dan pertalian habitat (habitat connectivity) Hutan Tropika di Asia Tenggara.

The lowland tropical forests of Southeast Asia are dominated by a single family of canopy and emergent trees, the Dipterocarpaceae. The seeds of dipterocarps are gravity or gyration dispersed. Short distance and limited seed dispersal via these mechanisms result in the aggregation of related individuals and strong fine-scale spatial genetic structure (FSGS). In logged and fragmented forests, where gene flow may be disrupted, tree species with strong FSGS are predicted to exhibit increased inbreeding, which consequently can erode genetic diversity, fitness and might limit the potential for natural regeneration of dipterocarps. Developing a set of indirect operational indicators for FSGS provides a solid basis for informing conservation and management of forest genetic resources in logged forests. Our main objective was to use an information theoretic approach to identify these indicators of FSGS in dipterocarps. We quantify FSGS in 19 dipterocarp species across four forest sites in Malaysian Borneo, India and the Seychelles. We detected FSGS in 15 (79%) of our study species, most of which displayed significant inbreeding. Our results suggest that wood density and flower size offer useful indicators of FSGS. We propose some simple guidelines to allow forest managers to account for FSGS when planning approaches to maintain genetically diverse stands in logged dipterocarp forests. The integration of improved understanding of genetic processes is essential for conserving forest tree genetic resources and ensuring the resilience of logged forests.

Less than half of anthropogenic carbon dioxide emissions remain in the atmosphere. While carbon balance models imply large carbon uptake in tropical forests, direct on-the-ground observations are still lacking in Southeast Asia. Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 per year (95% CI 0.14–0.72, mean period 1988–2010) in above-ground live biomass carbon. These results closely match those from African and Amazonian plot networks, suggesting that the world’s remaining intact tropical forests are now en masse out-of-equilibrium. Although both pan-tropical and long-term, the sink in remaining intact forests appears vulnerable to climate and land use changes. Across Borneo the 1997–1998 El Niño drought temporarily halted the carbon sink by increasing tree mortality, while fragmentation persistently offset the sink and turned many edge-affected forests into a carbon source to the atmosphere., The existence of a pan-tropical forest carbon sink remains uncertain due to the lack of data from Asia. Here, using direct on-the-ground observations, the authors confirm remaining intact forests in Borneo have provided a long-term carbon sink, but carbon net gains are vulnerable to drought and edge effects.

Developing a robust and cost-effective method for accurately estimating tropical forest’s carbon pool over large area is a fundamental requirement for the implementation of Reducing Emissions from Deforestation and forest Degradation (REDD+). This study aims at examining the independent and combined use of airborne LiDAR and Landsat 8 Operational Land Imager (OLI) data to accurately estimate the above-ground biomass (AGB) of primary tropical rainforests in Sabah, Malaysia. Thirty field plots were established in three types of lowland rainforests: alluvial, sandstone hill and heath forests that represent a wide range of AGB density and stand structure. We derived the height percentile and laser penetration variables from the airborne LiDAR and calculated the vegetation indices, tasseled cap transformation values, and the texture measures from Landsat 8 OLI data. We found that there are moderate correlations between the AGB and laser penetration variables from airborne LiDAR data (r = −0.411 to −0.790). For Landsat 8 OLI data, the 6 vegetation indices and the 46 texture measures also significantly correlated with the AGB (r = 0.366–0.519). Stepwise multiple regression analysis was performed to establish the estimation models for independent and combined use of airborne LiDAR and Landsat 8 OLI data. The results showed that the model based on a combination of the two remote sensing data achieved the highest accuracy (R2adj = 0.81, RMSE = 17.36%) whereas the models using Landsat 8 OLI data airborne LiDAR data independently obtained the moderate accuracy (R2adj = 0.52, RMSE = 24.22% and R2adj = 0.63, RMSE = 25.25%, respectively). Our study indicated that texture measures from Landsat 8 OLI data provided useful information for AGB estimation and synergistic use of Landsat 8 OLI and airborne LiDAR data could improve the AGB estimation of primary tropical rainforest.