Urbanization is generally thought to have a negative effect on wild bee communities. For example, increasing impermeable land surface is likely accompanied by decreased green space and reduced habitat and foraging for wild bees. Desire to lower the ecological impact of urbanization has led to the inclusion of green spaces and undisturbed areas into urban landscapes. Determination of the most effective size and shape of urban green spaces will help to maximize the benefits of these efforts. In particular, wild bee communities may be especially sensitive to green space fragmentation. To determine the impact of urban green space fragmentation on wild bee communities, this study sampled bees along an urban gradient in Southeastern Massachusetts, from 2016 to 2019. The ratio of forest edge to area at the spatial scales 300, 500, 750, and 1000m-radii was calculated using ArcGIS pro and used as a measure of fragmentation.
Results/Conclusions
The proportion of forest area and wild bee abundance was positively and significantly correlated at all spatial scales with the highest correlation at 1000m (R= 0.74; p < 0.05). Similarly, richness was positively and significantly correlated with the proportion of forest area at all spatial scales with the highest correlation at 1000m (R= 0.87; p < 0.05). Forest edge was negatively and significantly correlated with abundance at 750m (R= -0.75; p < 0.05) and 1000m (R= -0.63; p < 0.05), while negatively and significantly correlated with richness at 750m (R= -0.62; p < 0.05). Fragmentation (the ratio of forest edge to forest area) had a strong negative correlation with bee abundance at 750m (R= -0.82, p < 0.05) and 1000m (R= -0.86, p < 0.05), and a strong negative correlation with bee richness at 750m (R=-0.89, p < 0.05) and 1000m (R=-0.83, p < 0.05). These data suggest that increasing forest proportion and increasing fragmentation are both predictive of abundance and richness of wild bees in an urban setting. Optimization of green space size may help ameliorate the impact of urbanization on wild bee communities.