Local and landscape effects on arachnids in multistrata agroforestry systems: a global synthesis

Agroforestry systems are increasingly promoted as biodiversity-friendly production systems, yet the responses of non-insect arthropods to habitat structure and landscape context remain poorly synthesized. Arachnids play important roles in trophic regulation and ecosystem functioning, but their responses to agroforestry conditions have not been systematically assessed across spatial scales. We conducted a systematic review to evaluate how local and landscape-level variables influence arachnid assemblages in multistrata systems featuring perennial tree crops cultivated under a tree canopy. From 16 studies encompassing 88 reported relationships between explanatory variables and arachnid responses, we quantified the direction and consistency of effects using a directional index. Local-scale predictors showed a predominantly positive trend (directional index = + 0.35), with greater vegetation structural complexity, shade-tree diversity, canopy cover, and litter availability frequently associated with higher arachnid abundance, richness, or functional diversity. In contrast, landscape-scale predictors showed no consistent overall directional pattern (directional index = 0), reflecting the limited number of studies and variation in the spatial scales used to characterize landscape context . Overall, our synthesis indicates that structurally complex agroforestry systems can support diverse arachnid assemblages, highlighting the importance of maintaining vegetation complexity and resource availability within productive systems. The scarcity and heterogeneity of landscape-scale evidence represent a major research gap, limiting understanding of how landscape context shapes arachnid communities in agroforestry systems. By providing a scale-explicit synthesis, this study contributes to understanding arachnid responses to habitat structure and landscape context and identifies priorities for future research on biodiversity conservation in agroforestry landscapes.