The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼ 40,000 and ∼ 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼ 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼ 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

The marked biogeographic difference between western (Malay Peninsula and Sumatra) and eastern (Borneo) Sundaland is surprising given the long time that these areas have formed a single landmass. A dispersal barrier in the form of a dry savanna corridor during glacial maxima has been proposed to explain this disparity. However, the short duration of these dry savanna conditions make it an unlikely sole cause for the biogeographic pattern. An additional explanation might be related to the coarse sandy soils of central Sundaland. To test these two nonexclusive hypotheses, we performed a floristic cluster analysis based on 111 tree inventories from Peninsular Malaysia, Sumatra, and Borneo. We then identified the indicator genera for clusters that crossed the central Sundaland biogeographic boundary and those that did not cross and tested whether drought and coarse-soil tolerance of the indicator genera differed between them. We found 11 terminal floristic clusters, 10 occurring in Borneo, 5 in Sumatra, and 3 in Peninsular Malaysia. Indicator taxa of clusters that occurred across Sundaland had significantly higher coarse-soil tolerance than did those from clusters that occurred east or west of central Sundaland. For drought tolerance, no such pattern was detected. These results strongly suggest that exposed sandy sea-bed soils acted as a dispersal barrier in central Sundaland. However, we could not confirm the presence of a savanna corridor. This finding makes it clear that proposed biogeographic explanations for plant and animal distributions within Sundaland, including possible migration routes for early humans, need to be reevaluated.climate change | human migration | plant distribution | sea-level change

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To rehabilitate degraded forestlands and conserve the remaining forests in Kalimantan, effective measures are needed that accommodate various land uses in the landscape. We present a pragmatic model for prioritizing target areas for rehabilitation and discuss a potential approach, combining traditional reforestation and the forest management methods of local Dayak tribes with the operations of a commercial tree plantation venture, to promote the rehabilitation of elements of the tropical lowland rainforest. We characterized the vegetation and land use in the study area and assume that rehabilitation and conservation value will be maximized by concentrating rehabilitation efforts around forest patches with high cultural and economic value to the local Dayaks. We simulated potential enlargement of these culturally important forests and built a model to calculate a rehabilitation value for each forest fragment and fragment group with easily measurable criteria of vegetation and area. The model gives priority to areas where large continuous areas of culturally important forests already exist and/or will be created. The individual culturally important forest patches and their total area in the landscape are small, but even a small potential enlargement may be enough to establish relatively large concentrations. The potential matrix area for rehabilitation is dominated by young successional woody vegetation. Forested areas, although heavily degraded, connect several culturally important forest concentrations and are the most desirable target for rehabilitation. A well-managed commercial tree plantation can enhance conditions for the protection and rehabilitation of degraded forestlands through traditional reforestation and forest management methods.