Increasing urbanization creates environmental impacts on flora and human populations. The increase in impermeable surfaces drives rising urban temperature, surface water runoff, pollution, and pest abundance. Urban forests provide services that may mitigate some of these impacts. Benefits provided may be maximized by understanding urban stresses that effect tree condition. The study explores the relationship between tree condition and mortality to urban stresses, such as land cover and land usage. Canopy condition, as a metric of health, was expected to vary across the urban gradient and when analyzed at different spatial scales. This was explored by observing canopy condition in 200 street trees. Individuals of Tilia americana, Tilia cordata, Acer platanoides and Acer saccharnium were assessed within 1 km of intersecting transects along major roads of Toronto, ON. Across a gradient of urbanization, measured as proportion of impermeable surface, ArcGIS mapping tools and R programming language were used to determine landscape and site level impacts on tree condition. This study analyzed observations from 2018 – 2019 summers and make use of current and archival remote sensing landcover data. Determining the responses in tree condition in relation to environmental conditions will influence current local management and strategic plans for our urban landscape.
Results/Conclusions
Initial findings show tree geometry and size negatively relate to increases in paved surface area proportion. Lack of growing space, site histories and neighborhood age may play a role in addition to urban stresses directly influenced by increased paved surfaces, such as increased temperature and potential drought conditions. Though annual canopy condition did not significantly relate to impermeable percent cover, significant relationships between all tree species and spatial scales in relation to the proportion of paved surface were found. This suggests a strong relationship of urban conditions on overall growth, condition, and survival of these urban trees. The role of year to year variation in resource availability, temperature, and site history may explain some of the variation found in canopy condition. Further research will explore variation of resource allocation and estimated biomass to established allometric estimates in response to environmental conditions. Determining suitable predictive urban factors may inform management of species distributions to maximize urban forest services, control spread of non-native species, and forecast changes in urban forest health.