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Scale-dependent relationships between tree species richness and ecosystem function in forests
Author
Ryan A. Chisholm
Year
2013
Journal Title
Journal of Ecology
Institution
British Ecological Society
Pages
1-11
Call Number
JA0545-14
Keywords
biodiversity, biomass, complementarity, determinants of plant community diversity
and structure, productivity, sampling effects, species diversity, trees
Abstract:
1. The relationship between species richness and ecosystem function, as measured by productivity or biomass,
is of long-standing theoretical and practical interest in ecology. This is especially true for forests, which represent
a majority of global biomass, productivity and biodiversity.
2. Here, we conduct an analysis of relationships between tree species richness, biomass and productivity in 25
forest plots of area 8–50 ha from across the world. The data were collected using standardized protocols, obviating
the need to correct for methodological differences that plague many studies on this topic.
3. We found that at very small spatial grains (0.04 ha) species richness was generally positively related to productivity
and biomass within plots, with a doubling of species richness corresponding to an average 48%
increase in productivity and 53% increase in biomass. At larger spatial grains (0.25 ha, 1 ha), results were
mixed, with negative relationships becoming more common. The results were qualitatively similar but much
weaker when we controlled for stem density: at the 0.04 ha spatial grain, a doubling of species richness corresponded
to a 5% increase in productivity and 7% increase in biomass. Productivity and biomass were themselves
almost always positively related at all spatial grains.
4. Synthesis. This is the first cross-site study of the effect of tree species richness on forest biomass and productivity
that systematically varies spatial grain within a controlled methodology. The scale-dependent results are consistent
with theoretical models in which sampling effects and niche complementarity dominate at small scales, while
environmental gradients drive patterns at large scales. Our study shows that the relationship of tree species richness
with biomass and productivity changes qualitatively when moving from scales typical of forest surveys (0.04 ha) to
slightly larger scales (0.25 and 1 ha). This needs to be recognized in forest conservation policy and management.
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