Wild bee abundance in temperate agroforestry landscapes: Assessing effects of alley crop composition, landscape configuration, and agroforestry area

Agroforestry has the potential to provide multiple products and services from agricultural land, including bioenergy feedstock and habitat for wild bees. Our goal is to assess how variation in alley crop composition, landscape configuration, and total agroforestry area affects wild bee habitat in Illinois. First, different agroforestry crops may provide different floral and nesting resources for bees. Second, policy and economic factors may affect the total area and configuration of land devoted to agroforestry within a landscape. Third, farmers' operational preferences will affect area and configuration; they may be more willing to convert entire fields to agroforestry than to convert small patches within fields. We use the Lonsdorf model, a spatially explicit assessment of bee abundance, to model how wild bee habitat in hypothetical alternatives to an Illinois landscape is affected by alley crop composition (willow and row crops or willow and prairie), landscape configuration (alley cropping in subfield patches or in entire fields), and total alley crop area (12, 24, or 29% of the agricultural land). Our results indicate that the alley crop composition and area are important influences on the modeled nesting bee abundance index at the scale of both the landscape and the field. Although the configuration of agroforestry plantings significantly predicts bee abundance at the field scale, it is not an important factor when assessing bee abundance at the level of the landscape.