Yards increase forest connectivity in urban landscapes

Abstract

Tree canopy connectivity is important for supporting biodiversity. In urban landscapes, empirical examinations of habitat connectivity often overlook residential land, though yards and gardens often comprise a large portion of urban forests. We quantify structural composition (patches and paths), connectivity and fragmentation of an entire tree canopy network spanning 1220 Boston’s neighborhoods to assess the configuration of the urban forest potentially affecting tree-dependent wildlife species, such as some birds and arboreal mammals. The urban landscape was classified by land use, and residential yards were further subdivided into front yards, backyards, and corner yards. Structural composition, connectivity and fragmentation of the tree canopy was assessed using morphological spatial pattern and network analysis. Canopy metrics were then related to the land use of 349,305 property parcels. Back yard tree canopy cover was 65.23%. The majority of canopy links were on residential land (60.95% total), and particularly in backyards. Back yards contained the highest number of canopy fragments (48.65% total). Fragmentation of the canopy network peaked at ~ 23% of total canopy cover. Canopy fragmentation, distance among patches and their shape complexity were lower in neighborhoods with more tree canopy. The important role that yards have in sustaining canopy connectivity across urban landscapes poses challenges and opportunities. Urban land management and planning need to protect connectivity links within urban forests when located on private residential realm. A prioritization strategy aimed at expanding urban tree cover could focus on yards to ensure that urban landscape connectivity is maintained and increased.