Small-scale, diverse horticultural systems and semi-natural grasslands support complementary pollinator populations

Pollinating insects are of great importance in natural ecosystems and agricultural landscapes. Despite their crucial role for food production, safeguarding pollination services is becoming increasingly challenging due to pollinator declines. Habitat loss and agricultural intensification are among the main drivers, causing a substantial reduction in the availability of floral resources. Despite efforts, the uptake of measures to halt these declines in agricultural landscapes is low. Implementation of a novel crop production system is therefore proposed as a solution to ensure food security whilst concomitantly minimising environmental degradation and the associated biodiversity loss. Agricultural diversification is one such strategy that is known to promote multiple ecosystem services. Yet, the effects of agricultural diversification on pollinator populations in farm-scale, observational studies remains understudied. Here, we examine the importance of small-scale, diverse horticultural systems (SDHS) to support wild pollinator communities. Floral resources and wild pollinators were sampled in both SDHSs and semi-natural grasslands (SNG) in 16 landscapes in Flanders, Belgium. During late summer, these SNGs provide and important source of floral resources, thereby serving as a benchmark habitat to which the SDHSs are compared. Our study highlights the value of SDHSs as they provide diverse and abundant floral resources compared to SNGs. Moreover, pollinator species richness and abundance were comparable between the two habitats. Conversely, floral resource and pollinator community composition differed, indicating that different pollinator communities used the complementary resources provided by both habitat types. Furthermore, we show that SNGs represent the most specialised habitat type. We therefore argue that SDHSs can be considered to be an additional, complementary source of floral resources to those provided by SNGs. However, these SDHSs cannot substitute SNGs, given the importance of these grasslands for pollinators.