European agroforestry has no unequivocal effect on biodiversity: a time-cumulative meta-analysis

Abstract

Background Agroforestry is a production system combining trees with crops or livestock. It has the potential to increase biodiversity in relation to single-use systems, such as pastures or cropland, by providing a higher habitat heterogeneity. In a literature review and subsequent meta-analysis, we investigated the relationship between biodiversity and agroforestry and critically appraised the underlying evidence of the results. Results Overall, there was no benefit of agroforestry to biodiversity. A time-cumulative meta-analysis demonstrated the robustness of this result between 1991 and 2019. In a more nuanced view silvopastoral systems were not more diverse in relation to forests, pastures or abandoned silvopastures. However, silvoarable systems increased biodiversity compared to cropland by 60%. A subgroup analysis showed that bird and arthropod diversity increased in agroforestry systems, while bats, plants and fungi did not. Conclusion Agroforestry increases biodiversity only in silvoarable systems in relation to cropland. But even this result is of small magnitude, and single-study effect sizes were heterogeneous with sometimes opposing conclusions. The heterogeneity suggests the importance of other, usually unmeasured variables, such as landscape parameters or land-use history, influencing biodiversity in agroforestry systems.

Reply to: “Research on agroforestry systems and biodiversity conservation: what can we conclude so far and what should we improve?” by Boinot et al. 2022

“…In our recent meta-analysis [ 1 ], we have shown that agroforestry has no overall positive effect on biodiversity, but we found an effect of small magnitude comparing agroforestry with cropland. In a comment, Boinot et al [ 2 ] raised concerns about our definitions of agroforestry and biodiversity, the selection of the control sites used in our meta-analysis and the applicability of our results for conservation.…”

“…Indeed, we have included studies for which control locations were close to the treatment sites and this may potentially underestimate the effect of agroforestry on biodiversity. We have tested whether this was the case by excluding the sites that Boinot et al regard as inappropriate [for code and data see Additional file 1 and 2 ]. The conclusion from the meta-analysis did not change after discarding the case-control comparisons criticized (Fig.…”

Research on agroforestry systems and biodiversity conservation: what can we conclude so far and what should we improve?

“…Despite the strong enthusiasm of the agroforestry research community, a recent systematic review of agroforestry experiments in the Global South concludes that rigorous evidence on the effects of agroforestry on agricultural productivity, ecosystem services, and human well-being remains extremely limited [ 63 ]. Similarly, through their meta-analysis, Mupepele et al [ 1 ] point out that we should not take for granted the positive effects of agroforestry on biodiversity. We add that we should not prematurely underestimate the potential of agroforestry either.…”

“…We carefully read the protocols of studies comparing agroforestry systems with arable crops or open pastures, as our primary interest is the benefit of agroforestry systems in agricultural landscapes. We found that at least 11 out of 28 studies included in the meta-analysis by Mupepele et al [ 1 ] did not have adequate control sites. Many studies were designed to assess the distribution of taxa within agroforestry systems [ 7 – 11 ], not to assess the effect of agroforestry relative to other cropping systems.…”

“…In their meta-analysis, Mupepele et al [ 1 ] defined agroforestry as a “collective name for diverse land-use systems integrating tree husbandry with livestock or arable cultivation”. Fields bordered by riparian fields margins and hedgerows were excluded as “they are not really under silvicultural use”.…”