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| Aim Global patterns in primary productivity in natural ecosystems are important
for interpreting ecological processes and patterns of biodiversity. Net primary
productivity (NPP) on land has long been thought to be greatest in tropical forests
and to decrease towards the poles. However, it has recently been claimed that the
NPP of mid-latitude forests is as great as, or even greater than, that of tropical
forests and that ecologically relevant productivity peaks at mid-latitudes. Here we
evaluate these hypotheses by testing for relationships between latitude and productivity
using a range of forest productivity datasets.
Location Global.
Methods We apply ordinary least squares regression and t-test analyses to published
latitude–productivity data for forests, specifically updated to include an
expanded dataset for the previously data-poor tropics, and we evaluate the relationship
between the primary productivity of forests and modelled vascular plant
species richness.
Results Contrary to the recent claims, we found strong support for a negative
relationship between latitude and annual NPP of forests with all datasets, and NPP
was significantly greater in tropical forests than in temperate forests.Vascular plant
richness was positively correlated with NPP.
Main conclusions NPP of forests increases towards the equator. Given that
species richness also increases towards the equator, and that vascular plant richness
correlates with NPP, these results are consistent with recent meta-analyses showing
that the relationships between productivity and species richness of both plants and
animals in natural ecosystems are predominantly positive. These results are congruent
with ecological theories that predict a positive relationship between species
richness and productivity, and they indicate that there is no need to explain peaked
richness–productivity relationships over broad spatial extents, since they do not
appear to exist. | |
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