The Lawn is Buzzing: Increasing insect biodiversity in urban greenspaces through low-intensity mowing

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The Lawn is Buzzing: Increasing insect biodiversity in urban greenspaces through low-intensity mowing

Abstract

Greenspaces have become the anvil where stewards and practitioners are forging innovative, evidence-based actions to meet biodiversity targets in urban environments, catalysing a wave of co-designed research/practice projects aimed at assessing the ecological changes brought about by urban greening and generating the evidence that biodiversity objectives are being met. Their full potential often remains unrealised due to entrenched management practices, as best exemplified by high-intensity mowing, which has given rise to the most ubiquitous greenspaces feature worldwide: the turfgrass lawn. Lawns are notoriously deficient at supporting insect communities due to their simplified vegetation structure and low plant diversity, and the compounded effect of frequent mowing on forb growth, which limits their capacity to come into flower and supply floral resources to pollinators and other flower visitors. Addressing these shortcomings can be readily achieved by reducing mowing intensity, resulting in greater vegetation height, flower cover and plant diversity – effectively transforming lawns into a more complex grassland-type ecosystem. This approach is particularly enticing to practitioners pursuing positive, cost-effective biodiversity outcomes while upholding their commitment to core ecological restoration and biodiversity conservation projects.

Here, we demonstrate how transitioning a lawn from high- to low-intensity mowing regimes led to pronounced increases in the number of indigenous insect species, evident both for the whole community and on assemblages of functionally similar species, including detritivores, herbivores, predators, parasitoids and pollinators. We further identify a positive effect of vegetation height on the community and species-specific probabilities of occurrence of indigenous species, which was consistently strong for detritivores, herbivores and parasitoids. We also show that the number of indigenous species associated with our low-intensity mowing treatment markedly exceeded that of 43 high-intensity mowed lawns previously surveyed throughout the study area, and that the effect of vegetation height across our field experiment gradient was substantially stronger than that of the existing high-intensity lawns gradient. Our findings provide compelling evidence that reducing lawn mowing intensity yields positive ecological outcomes for functionally diverse indigenous insect communities, charting a course for stakeholders tasked with demonstrating how evidence-based greening actions can be a sound investment to meet local, regional and global biodiversity targets.

Keywords: Co-design, Detritivores, Flower-visitors, Functional assemblages, Greening, Hierarchical community models, Nature in cities, Parasitoids, Pollinators, Predators, Urban ecology, Urban environments