Ecological Indicators (Oct 2023)
Are bees attracted by flower richness? Implications for ecosystem service-based policy
Abstract
Agri-environmental policies aim to reverse the degradation of ecosystem services in rural landscapes by implementing biodiversity-based land-use solutions. One such agri-environmental measure is the contract for bee-forage fields in Estonia. We developed a multi-site experiment to estimate the effect of plant diversity on the quality properties of flower-based services, such as flowering duration (indicating functional stability) and the foraging activity of insect pollinators (indicating functional intensity). Each site consisted of eight randomly ordered strip-segments forming a flower diversity gradient.The period of abundant flowering was longer in all kinds of species mixture than in monocultures. However, the foraging activity of honey bees and bumblebees was greatest in monocultures and in a low-diversity mixture, while a balanced high-diversity mixture was least attractive. Foraging activity was lowered when an abundant melliferous plant species was flowering within a high-diversity mixture (i.e. high species richness, but low evenness). The extended flowering of species mixtures did not compensate for the lower daily visitation rate.We challenge the largely biodiversity-oriented agricultural policy designs. This case study provides evidence that plant species richness is not a comprehensive indicator of the service provision quality of an ecosystem. Specifically, low-diversity flower areas are the best foraging sites for bees and other flower visitors. A field mosaic of various monocultures and low-diversity mixtures seems to be the ecologically most efficient rural landscape design to support bees and other potential pollinators. Suggested and marketed pollinator-oriented seed mixtures should be quantitatively tested for ecological efficiency.
