Abstract
We report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha−1 (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha−1) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- compared with neotropical forests. However, mean stem density is low (426 ± 11 stems ha−1 greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus–AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes.
Highlights
Comparative studies of the above-ground biomass (AGB) of tropical forests exist for South America [1,2,3] and Asia [4] but not for Africa
We identify the spatial filters significantly correlated with the residuals from the ordinary leastsquares (OLS) model, and re-run the identical explanatory variables as in the OLS model plus the selected filters, termed spatial eigenvector mapping (SEVM) models
C : N ratio was negatively related to AGB, i.e. higher phosphorous availability is related to higher AGB
Summary
Comparative studies of the above-ground biomass (AGB) of tropical forests exist for South America [1,2,3] and Asia [4] but not for Africa. A third possible class of effect is associated with the species pool available in a given forest that may systematically elevate or depress AGB via effects on either NPPWOOD or tw This may be important given evidence of the relationship between geology and tree species distributions [12,13], and contribute to the high AGB in Southeast Asian forests dominated by Dipterocarpaceae [4,6]. Amazonian AGB was not significantly related to mean annual air temperature, wood production was, negatively associated with it [3], and in Asia most of the best models relating AGB to environmental conditions do not include temperature [4], suggesting any AGB –temperature relationship may be relatively weak, or is being masked by other covarying factors We consider both temperature and precipitation as potential drivers of spatial variation in AGB.
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