For meta-analyses, a minimum of primary studies is required to compute a meaningful summary effect . Boinot et al. point out that it is too early for a meta-analysis on alley cropping agroforestry systems given that there are few studies with an unbalanced sampling of age and taxonomic groups. As we have not computed a summary effect size for alley cropping and it is not even an existing category in our meta-analysis, we assume that silvoarable systems are meant here. We agree that too few studies in silvoarable systems exist for each age and taxonomic group to derive very robust conclusions.
However, in the same breath, Boinot et al. conclude that our meta-analysis ‘most likely underestimates the positive effects’. We wonder about such a conclusion on ‘likely positive effects’ that are necessarily based on the same few primary studies that are said to be too few for meta-analysis. In the absence of good primary studies, no general conclusions can be drawn in either direction and it is unjustified to assume that there must be a strong positive effect of agroforestry on biodiversity. We however think that even with a low number of primary studies, a quantitative synthesis in form of a meta-analysis will outcompete the statement of each individual study and allow more general and evidence-based conclusions . Thus a systematic research synthesis increases the evidence base, even by including only few effect sizes . We also agree that there is room for improvement and welcome future and complementary efforts on different aspects of land use, biodiversity and by increasing the number of primary studies.
The effect of agroforestry on biodiversity may be influenced by local differences as Boinot et al. point out. We agree that local differences should be considered, if they have an influence on the impact of agroforestry on biodiversity. We want to remind that a fundamental idea of evidence-based practice is the identification of a causal link between an impact, e.g. a conservation measure, and an outcome of interest . These direct links are difficult to determine if unmeasured and locally differing variables additionally influence the outcome of interest, which is often the case in ecology. Consequently, the transferability of study results from one local context to another is not straightforward. Nevertheless, in the absence of knowledge about the local conditions under which agroforestry may be or not be beneficial for biodiversity, a meta-analysis across many local contexts synthesising systematically searched literature, is the best and most generalisable evidence we can have.