The Dahomey gap is a savanna region separating the West African rainforests to two regions. We set two sites in this woody savanna, at north and south regions in purpose to examine the differences in tree community properties between sites and among canopy-closure types, and to reveal the factors affecting the differences. Two sites are ca. 225 km distant from each other and have different rainfall patterns. Six 1-ha plots in each site were studied, which cover three types of canopy-closure (closed, semi-open and open). We recorded 3,720 trees that are equal to or more than 5 cm diameter at the breast height, consisted of 70 species belonging to 34 families. Most abundant three species, Isoberlinia doka, Vitellaria paradoxa and Pericopsis laxiflora appeared in both sites. The detrended correspondence analysis (DCA) based on species abundance divided 12 plots into groups of north and south sites along the first axis, whereas canopy-closure types were not associated with DCA axes. At any given total tree height, trees in the north site had slenderer stems with narrower crowns than those in the south site. The specific leaf area was smaller in the north site. Between-site differences in species abundance and allometry are possibly driven by rainfall variation.

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Sparse vegetation (i.e. savannah and woodland) interspersed with patchy forests (i.e. rain forest and montane forest) is typical of many tropical regions. Forest trees seldom establish adjacent to these sparsely vegetated areas because the adjacent vegetation is often more resistant to fire and water stress, and competition from grass species. However, these limiting factors may not apply under a closed crown due to a facilitative effect. Here the effect of a closed crown on the establishment of montane forest trees in miombo woodland in northern Malawi was determined. Environmental conditions, the number of saplings of montane forest trees and their regeneration mode were all studied. Result showed that grass cover is reduced and water stress can be ameliorated under a closed crown of Brachystegia boehmii and Brachystegia floribunda, which are the dominant trees of miombo woodland. Numerous montane forest tree saplings were found under the closed crown. These results indicate that a closed crown of B. boehmii and B. floribunda has a facilitative effect on the establishment of montane forest tree in miombo woodland.

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Nutrient inputs via litterfall and associated nutrient accumulations and releases in the litter layer were investigated in 7-year-old Acacia mangium Willd. plantation stands in Indonesia. Annual N, Mg, Ca and K inputs via litterfall were 230-235, 21-26, 157-179 and 131-157kg ha^-1 yr^-1, respectively and the contributions of phyllode litterfall to these nutrient inputs were over 60%. Nutrient inputs via litterfall increased from dry to wet seasons being strongly associated with reproductive litterfall inputs as well as phyllode litterfall inputs. Annual mean N, Mg, Ca and K accumulations on the forest floor were 172-235, 12-14, 52-88 and 42-47kg ha^-1, respectively. There were no clear seasonal variations in nutrient amounts on the forest floor. The peak of mass loss of phyllode litter was observed in the late wet seasons, and its seasonal change was coincided with the rainfall seasonality. Reflecting mass losses of reproductive and twig litters, however, seasonal variability in mass loss of whole litter became more complex. Nitrogen and Mg releases from litter layer tended to increase in the late wet seasons being affected by the retarded releases of these nutrients from fleshly fallen litters in addition to the increased mass loss of phyllode litter in the periods. Calcium releases from litter layer showed no significant seasonal variations reflecting the irregular seasonal changes in Ca release from twig litter rich in Ca. Meanwhile, the seasonal variation in K release from litter layer coincided with the seasonal changes in K inputs via litterfall.

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We tested the hypothesis that soil microbial activity in an Acacia mangium plantation in South Sumatra, Indonesia, is limited by phosphorus (P) availability and not nitrogen (N) availability. An incubation experiment was conducted and soil respiration rates were measured after the addition of glucose, N, and P in different combinations on soil samples obtained from an Acacia mangium plantation. Results showed that P addition significantly stimulated CO₂ emissions, suggesting that soil microbial activity in the studied Acacia mangium plantation is limited by P availability. P addition also increased microbial P, supporting our suggestion. Meanwhile N addition did not increase, rather reduced CO₂ emissions, showing that N was not the main limiting factor for microbial activity in the studied soil. However, N addition significantly increased microbial N, implying that the composition of the microbial community changed. Our study suggests that P fertilization to an Acacia mangium plantation might stimulate the soil microbial activity to accelerate the soil organic matter decomposition.

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