Agricultural systems face several challenges that threaten their capacity to feed the world while maintaining a healthy and functional environment. Climate change, together with soil degradation, biodiversity loss, resource scarcity and invasive species, is a major threat to agricultural systems worldwide. In this context, new practices have been proposed to circumvent or minimize these threats. Yet, these mostly focus on the farm or plant level (e.g., breeding for stress‐tolerant species), while frequently overlooking belowground components (e.g., soil organic carbon accrual). By interlinking above‐ and below‐ground components, the likelihood of limiting the negative effects of current threats to agricultural systems can be maximized. This review explores current knowledge regarding agroforestry and its effects on belowground components as a key property in the reducing effects of climate change. We first review tree effects on key soil properties of agricultural systems. We synthesize evidence regarding agroforestry systems response to current environmental threats that are related to climate change. We continue by discussing how soil processes play a fundamental role in the capacity of agroforestry systems to cope with climate change. We conclude by proposing options on how resilience of agroforestry systems could be further enhanced.

Summary: The ability of soil microbial communities to withstand and recover from disturbance or stress is important for the functional stability of forest ecosystems. However, the relationship between the community responses of soil microbes and variation in tree mixtures vs functional composition remains poorly understood. We investigated soil biochemical properties and soil microbial resistance and resilience to drought in three 4‐year‐old tree monocultures (Acer saccharum Marsh, Larix laricina (Duroi) K. Koch and Pinus strobus L.) and two tree species combinations (L. laricina/A. saccharum and L. laricina/P. strobus) planted in a high‐density tree field experiment located in southern Quebec, Canada. The experimentally imposed drought stress consisted of maintaining soil material for 30 days at 25% of water‐holding capacity (WHC). Microbial biomass was assessed immediately after the water stress (resistance) and 15 and 30 days following drought (resilience). Results showed that tree communities influenced soil chemistry, soil respirometry properties and microbial resistance and resilience. We measured significant non‐additive (i.e. both synergistic and antagonistic) effects of mixing tree species in some of the soil biochemical properties measured, mostly in the L. laricina/A. saccharum mixture. However, we did not find non‐additive effects of tree mixtures on microbial resistance and resilience. A structural equation modelling analysis revealed that resistance and resilience were mostly modulated by direct effects of community‐weighted means (CWM) of leaf litter lignin content and mineralizable N, and by indirect links from tree density and CWM of leaf litter N content via mineralizable N. This study suggests that tree species identity surpassed species mixtures as a key driver of soil microbial resistance and resilience. We showed a trade‐off between microbial resistance and resilience in soil food webs, which is consistent with ecological theory. Our results indicate that differences in functional traits between tree species may rapidly be reflected in divergent soil biochemical properties and that these differences can in turn drive soil microbial resistance and resilience to drought.

In comparison with conventional agriculture, agroforestry systems improve the delivery of multiple ecosystem services and support greater biodiversity. Yet, the effects of agroforestry on various ecosystem services and biodiversity vary worldwide between climatic regions and system types, and studies often focus on measuring a small number of services or biodiversity indicators. We conducted a quantitative summary of multiple large‐scale meta‐analyses comparing service delivery or biodiversity between agroforestry systems and conventional agricultural systems to capture the global effect of agroforestry on agroecosystem multifunctionality. Data were aggregated from 20 meta‐analyses, many of them global, and response ratios were calculated to assess relative effects of agroforestry systems worldwide on multiple categories of biodiversity indicators and production, regulation, and support services. By combining different datasets that addressed specific ecosystem services or biodiversity indicators and analyzing 3075 comparisons between agroforestry systems and their conventional counterparts, we found that agroforestry enhanced ecosystem service delivery and biodiversity globally by an average of 23%. The effects were more pronounced on supporting and regulating services and biodiversity than on production services. The vast majority of analyzed services and biodiversity indicators were enhanced in agroforestry systems, while few were either not affected or affected negatively. Among ecosystem services analyzed along an aridity gradient, only soil organic carbon (SOC) stocks and forage production varied significantly. The positive effects of agroforestry on SOC stocks were stronger in drier conditions, while those on forage production followed a quadratic trend, with maximal benefits in arid conditions. Our results suggest that broad‐scale adoption of agroforestry in conventional agriculture could benefit agroecosystem multifunctionality globally without sacrificing productivity and would help support sustainable food production.