Are small greening areas enhancing bird diversity? Insights from community-driven greening projects in Boston

Green space is an important component of the urban landscape, providing ecosystem services for city dwellers and supporting biodiversity. In many Gities, green space is concentrated in large areas, while the rest is dispersed in small patches like pocket parks, gardens or street trees. Such small-scale green space is often the target of greening initiatives but little is known about their value for supporting and conserving biodiversity. To assess the value of such initiatives for biodiversity, we used birds as an indicator. We examined bird communities at small greening projects (n = 12), nearby randomly chosen urban sites (n = 12), and large parks (n = 6) in Boston, MA, in relationship to underlying landscape patterns. Our results show that large parks harbor a distinct and rich bird community. The other sites, regardless of the presence of greening projects, were very similar to each other. However, most sites with greening projects had higher species richness than the random urban site in their vicinity. The main factor associated with this appears to be the patch size of green space and to a lesser extent, tree cavities. Even small increases of a few hundred square meters were associated with an increase in bird richness. Having more trees with cavities was also beneficial for species richness. Small greening projects appear to be most valuable for urban biodiversity if they target preserving, increasing and connecting existing green space. This may represent a tradeoff with environmental justice criteria for new green space. (C) 2013 Elsevier B.V. All rights reserved.