Influence of within-field understory vegetation strips on plant and invertebrate communities in alley cropping agroforestry systems

Sébastien Boinot defended his PhD thesis on agroforestry in the "Tropical and mediterranean cropping system functioning and management” joint research unit (UMR System), which is under the authority of the CIRAD Performance of Tropical Production and Processing Systems department (Persyst), the INRA Environment and Agronomy department (EA), the Montpellier SupAgro Environments, Production, Resources and Systems department (MPRS) and the CIHEAM-IAMM.

The current intensive food production is one of the main causes of biodiversity extinction worldwide. Alley cropping agroforestry, in which arable crops are grown between tree rows, represents a great opportunity for the reintegration of semi-natural habitats within fields. Tree rows are associated with non-crop vegetation, hereafter called understory vegetation strips (UVS). Given the spatial configuration and the important extent of UVS within crop fields, it is likely that both the dispersal of living organisms and the amount of refugia for biodiversity are increased in alley cropping agroforestry compared to pure crop systems.

This could result in enhanced ecosystem services and/or disservices, depending on the nature of favored species (e.g. competitive weeds, invertebrate pests, natural enemies). The objective of this PhD thesis was to describe the response of plant and invertebrate communities to alley cropping agroforestry and farming systems (conventional vs organic) and assess both the positive and negative effects of UVS on biodiversity conservation and biological control of weeds and crop pests.

A production field network was used to sample plant and invertebrate communities in alley cropping agroforestry systems and pure crop controls, while an experimental site was used to study invertebrate overwintering in agroforestry systems. We described both the taxonomic and functional structures of communities to better understand their responses to agroforestry systems and, for invertebrates, their potential effects on biological control.

Our studies confirmed that UVS are valuable habitats for plant and invertebrate diversity conservation. UVS do not appear to be a source of troublesome weeds or to favor the overwintering of dominant pests, but greatly affect the spillover of ground-dwelling predators in negative or positive ways depending on the farming system.

The results obtained from this PhD thesis fill a knowledge gap about the biodiversity of temperate agroforestry systems and provide insights for the management of agroecological infrastructures, which are established to favor functional biodiversity and reduce the use of agrochemicals.

Picture of the PhD thesis cover of Sébastien Boinot taken in one of the alley cropping agroforestry fields surveyed in the Gers department, South West France.