Climate sensitivity and radial growth of five urban tree species in Toronto, Canada

Source abstract

Urban trees provide critical ecosystem services yet face compounding stressors from anthropogenic climate change and the urban heat island. We investigated the impact of climate on radial growth of five commonly planted tree species in Toronto (Canada): red oak ( Quercus rubra ), sugar maple ( Acer saccharum ), Norway maple ( Acer platanoides ), European linden ( Tilia spp.), and Austrian pine ( Pinus nigra ). Increment cores were collected from 179 trees growing both along city streets and trees growing in urban parks. Static and moving correlation analyses were used to evaluate relationships between detrended ring-width chronologies and monthly temperature and precipitation, and generalized additive mixed models (GAMM) were used to compare basal area increment (BAI) trends between species and locations. Norway maple and sugar maple showed significant negative correlations with summer temperature that have strengthened in recent decades, coinciding with declining BAI. Park red oak and Park linden had the highest BAI and showed limited climate stress, although red oak growth is increasingly negatively related to summer temperature, and Street red oak and Street linden have declined over the past decade. Differences between park and street trees were species-specific: Street Norway maple grew consistently more slowly than Park Norway maple, Street linden and Street red oak have recently fallen behind their park counterparts, and no location effect was found for sugar maple or Austrian pine. Austrian pine showed little climate sensitivity but relatively low BAI. These results highlight species- and location-specific vulnerabilities of Toronto’s urban forest to ongoing climate change, with implications for urban forest management for cities with humid continental climate conditions.