Data from: Land-use intensity and the effects of organic farming on biodiversity: a hierarchical meta-analysis

The benefits of organic farming to biodiversity in agricultural landscapes
continue to be hotly debated, emphasising the importance of precisely
quantifying the effect of organic vs. conventional farming. We conducted
an updated hierarchical meta-analysis of studies that compared
biodiversity under organic and conventional farming methods, measured as
species richness. We calculated effect sizes for 184 observations garnered
from 94 studies, and for each study we obtained three standardised
measures reflecting land-use intensity. We investigated the stability of
effect sizes through time, publication bias due to the ‘file-drawer’
problem, and consider whether the current literature is representative of
global organic farming patterns. On average, organic farming increased
species richness by about 30%. This result has been robust over the last
30 years of published studies and shows no sign of diminishing. Organic
farming had a greater effect on biodiversity as the percentage of the
landscape consisting of arable fields increased; i.e. it is higher in
intensively farmed regions. The average effect size and the response to
agricultural intensification depend on taxonomic group, functional group,
and crop type. There is some evidence for publication bias in the
literature; however, our results are robust to its impact. Current studies
are heavily biased towards Northern and Western Europe and North America,
while other regions with large areas of organic farming remain poorly
investigated. Synthesis and recommendations. Our analysis affirms that
organic farming has large positive effects on biodiversity compared with
conventional farming, but that the effect size varies with the organism
group and crop studied, and is greater in landscapes with higher land-use
intensity. Decisions about where to site organic farms to maximise
biodiversity will, however, depend on the costs as well as the potential
benefits. Current studies have been heavily biased towards agricultural
systems in the developed world. We recommend that future studies pay
greater attention to other regions, in particular, areas with tropical,
subtropical and Mediterranean climates, in which very few studies have
been conducted.