Direct and indirect effects of agricultural land cover on avian biodiversity in eastern Canada

Abstract

Agriculture is one of the largest threats to global biodiversity. However, most studies have focused only on the direct effects of agriculture on biodiversity, and few have addressed the indirect effects, potentially over or under-estimating the overall impacts of agriculture on biodiversity. The indirect effect is the response not to the agricultural cover types or operations per se, but instead, to the way that agriculture influences the extent and configuration of different types of natural land cover in the landscape. We used structural equation modelling (SEM) to evaluate the direct, indirect, and total effects of agriculture on species richness of three bird guilds: forest birds, shrub-edge birds, and open country birds. We found that forest bird richness was driven by the negative indirect effect of cropland via forest loss. Shrub-edge and open country bird richness increased with the amount of agriculture land covers; however, importantly, we found negative indirect effects of agriculture on both guilds via a reduction in more natural land covers. This latter result highlights how we would have over-estimated the positive effects of agriculture on shrub-edge and open country bird richness had we not measured both direct and indirect effects (i.e., the total effect size is less than the direct effect size). Overall, our results suggest that a bird-friendly agricultural landscape in our region would have forest that is configured to maximize forest edge, and a high proportion of perennial forage within the agricultural portion of the landscape.

Local and regional‐scale effects of hedgerows on grassland‐ and forest‐associated bird populations within agroecosystems

“…For example, species such as eastern phoebe, which had weak but nonsignificant positive associations with LWFs at the local scale, tended to be most strongly influenced by the proportion of forested habitat in more natural areas and LWFs in agriculturally intensive regions. Strategies that maximize forest edge within agroecosystems by combining small forest or shrub retention patches with LWFs may be most effective in supporting populations for a greater range of species (Rabbetts et al, 2023).…”

Bird and Bat Diversity and Abundance in Agroecosystems in Relation to Drainage Hedgerow and Landscape Structure

“…found a positive effect of forest amount on forest bird diversity and abundance in roadside surveys of forest area-sensitive birds in urban and agricultural landscapes Rabbetts et al (2023). found a negative association between forest bird species richness and cropland amount, which they attributed to the indirect effects of loss of forest cover.…”