Alley cropping agroforestry systems: Reservoirs for weeds or refugia for plant diversity?

Promoting generalist predators of crop pests in alley cropping agroforestry fields: Farming system matters

“…However, alley cropping alone was not enough to promote predominantly seedfeeding carabids (granivorous and omnivorous) and cursorial spiders in crop alleys. The presence of overwintering habitats and trophic resources in UVS might not have compensated for the very poor weed flora observed in fields under conventional farming (Boinot et al, 2019a). Indeed, previous studies have shown that organic farming favors seed-feeding carabids and spiders (Feber et al, 1998;Batáry et al, 2012;Diekötter et al, 2016), presumably because of the presence of a rich and abundant weed flora that provides additional habitats (e.g.…”

“…Climate is sub-Atlantic (hot summers and cool winters) and annual precipitation usually varies from to 900 mm. From a previous study assessing the effect of alley cropping on plant communities (Boinot et al, 2019a), vegetation surveys were carried out in May 2017 in fields growing either winter wheat (Triticum aestivum L.) or winter barley (Hordeum vulgare L.), half under conventional farming and half under organic farming (i.e. generally more diverse crop rotations, without pesticides and inorganic fertilizers).…”

“…Conversely to our expectations, granivorous carabids (mostly represented by Harpalus dimidiatus) and cursorial spiders were even less active in crop alleys than in pure crop controls under conventional farming. In alley cropping systems, they probably foraged in UVS where plant and invertebrate resources are more abundant and diversified than in crop alleys (Boinot et al, 2019a;Boinot et al, 2019b), resulting in a retention effect. This result is consistent with those from Wamser et al (2011), who showed that high availability of overwintering habitats in the landscape reduces or delays the spillover of carabid beetles in fields under conventional farming.…”

“…First, the total activity-density of seed-feeding carabids (granivorous and omnivorous) was doubled in crop alleys of alley cropping systems as opposed to pure crop controls. This could be explained by (i) the presence of UVS that are favorable overwintering habitats for seed-feeding carabids in alley cropping systems (Boinot et al, 2019b), and (ii) a rich and abundant weed flora enhancing habitat and resource availability under organic farming, including associated phytophagous and detritivore prey (Batáry et al, 2012;Diehl et al, 2012;Boinot et al, 2019a), thereby favoring the spillover of predators associated to UVS towards crop alleys (i.e. source effect).…”

“…This increased interspersion of AEI and cropped areas within fields themselves can affect ecosystem service flows (Mitchell et al, 2015). Although very few studies have focused on the ecological functions of UVS, it has been shown that they are important refugia for many plants and invertebrates (Boinot et al, 2019a;Boinot et al, 2019b;Pardon et al, 2019;D'Hervilly et al, 2020). UVS provide overwintering habitats for most spiders and for carabid species sensitive to agricultural intensification (characterized by a predominantly granivorous diet and a large body length), whereas small and carnivorous carabids overwinter mostly in crop alleys (Boinot et al, 2019b).…”