Abstract
Abstract. Understanding the relationships between plant traits and ecosystem properties at large spatial scales is important for predicting how compositional change will affect carbon cycling in tropical forests. In this study, we examine the relationships between species wood density, maximum height and above-ground, coarse wood production of trees ≥10 cm diameter (CWP) for 60 Amazonian forest plots. Average species maximum height and wood density are lower in Western than Eastern Amazonia and are negatively correlated with CWP. To test the hypothesis that variation in these traits causes the variation in CWP, we generate plot-level estimates of CWP by resampling the full distribution of tree biomass growth rates whilst maintaining the appropriate tree-diameter and functional-trait distributions for each plot. These estimates are then compared with the observed values. Overall, the estimates do not predict the observed, regional-scale pattern of CWP, suggesting that the variation in community-level trait values does not determine variation in coarse wood productivity in Amazonian forests. Instead, the regional gradient in CWP is caused by higher biomass growth rates across all tree types in Western Amazonia. Therefore, the regional gradient in CWP is driven primarily by environmental factors, rather than the particular functional composition of each stand. These results contrast with previous findings for forest biomass, where variation in wood density, associated with variation in species composition, is an important driver of regional-scale patterns in above-ground biomass. Therefore, in tropical forests, above-ground wood productivity may be less sensitive than biomass to compositional change that alters community-level averages of these plant traits.
Highlights
Understanding the roles of species composition and abiotic factors on ecosystem properties at large spatial and temporal scales is important for predicting how feedbacks from compositional change might influence patterns of carbon cycling (Hooper et al, 2005)
We focus on the role of two traits, wood density and species maximum height, for determining the patterns of above-ground, coarse wood production of trees ≥10 cm diameter (CWP-Mg C ha−1 a−1) in Amazonian forests
There is a correlation between the functional composition and CWP of Amazonian forests (Fig. 3), our results suggest that the variation in trait values does not cause the regional variation in CWP (Table 3, Fig. 4)
Summary
Understanding the roles of species composition and abiotic factors on ecosystem properties at large spatial and temporal scales is important for predicting how feedbacks from compositional change might influence patterns of carbon cycling (Hooper et al, 2005). Spatial variation in average maximum height is less well-studied, but a pantropical comparison of the composition of the understorey community in several large plots, found that a Western Amazon forest had a high abundance of small stature species (LaFrankie et al, 2006). Such spatial variation in community-level traits implies that they could have an important role in determining variation in stand-level processes
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