Individual study: Ecological Compensated Areas (ECAs) have no consistent effect on biodiversity across taxa in Aargau, Switzerland
Roth T., Amrhein V., Peter B. & Weber D. (2008) A Swiss agri-environment scheme effectively enhances species richness for some taxa over time. Agriculture, Ecosystems & Environment, 125, 167-172
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Increase the proportion of semi-natural habitat in the farmed landscape
A 2007 site comparison study of 516 survey points across the canton of Aargau, Switzerland (Roth et al., 2008) found no consistent effects on biodiversity across taxa. For birds, plants and butterflies, but not for snails, there were more species on Ecological Compensation Area (ECA) than non-ECA sites in the first survey (9.7 vs 7.7 bird species, 19.2 vs 14.6 plant species and 7.3 vs 5.6 butterfly species on ECA and non-ECA sites respectively). There were 4-5 snail species on both ECA and control sites. Changes over time were different on ECA plots than non-ECA plots for plants and snails, but not for birds and butterflies. Between the first survey (1996-2000) and the second survey (2001-2005), numbers of vascular plant and snail species increased on ECAs (by 5.1 and 1.4 species, respectively) but not on non-ECA fields. Across the whole landscape, the number of bird species increased and the number of butterfly species decreased between the two surveys, but the changes were similar on ECA and non-ECA sites. Sampling was based on a regular 2 x 2 m grid system across the entire 1403 km² of the canton of Aargau. Plants, birds, butterflies and snails were surveyed at each grid point. Whether the land or some of the 100 m radius circle plot (for the bird survey) were designated as ECA was recorded. All plots were surveyed twice, five years apart, with the first survey taking place in 1996-2000 and the second in 2001-2005. The authors note that ECAs were typically established on farmland with potential for maximum biodiversity gain, which may have affected the relative numbers of species found in the first survey.
Increase the proportion of natural/semi-natural vegetation in the farmed landscape
A 2007 site comparison study of 181 plots in the canton of Aagau, Switzerland (Roth et al. 2008), found that, on average, two more bird species were identified in ecological compensated areas (10 species on average) than in non-ecological compensated areas (9 species). Although on average two more bird species were found in the second set of surveys (carried out from 2001-2005) than in the first set (1996-2000), this increase was uniform in both ecological compensated areas and non-ecological compensated areas. One hundred and twenty 100 m radius circle plots that contained some land designated as an ecological compensated area were compared with 61 plots not containing any ecological compensated areas. The authors note that ecological compensated areas were typically established on promising farmland with the potential for “maximum biodiversity gain”, which may have affected the relative species richness of ecological compensated areas and non-ecological compensated areas.