PS 29-149
Selecting trees for urban forests in the California Central Valley using climate specific risk factors
Urban forests are green infrastructure investments that provide many socio-ecological benefits to society. However, the perpetuation of these benefits depends on urban forests’ resilience to stress brought on by global change, in particular, climate change. Projected climatic shifts will change temperature, precipitation and the incidence of pest, disease and storm patterns. The tolerance of urban trees to these stressors varies considerably among species. The United States Forest Service, Urban Ecosystems and Social Dynamics Program, collected 29 urban tree inventories from across the state of California. These data were then used to develop municipal tree inventory report cards for each municipality based on risk factors of over-abundance, age and overall pest vulnerability. These report cards have since served as a valuable tool for scientists, managers and the general public to assess and adapt their urban tree planting strategies. We have expanded this tool to include risk factors based on climate change; increased minimum temperatures, drought, pest damage, species invasiveness, habitat specificity and storm severity. The objective was to create a tool which would assist managers in choosing appropriate tree species based on projected changes in their urban ecosystem resulting from climate change.
Results/Conclusions
We focused our effort on the California Central Valley, using USDA Hardiness Zones, which is projected to be home to 11.4 million people in 2040. Using eight municipal urban tree inventories, we determined which tree species are most important based on their relative basal area abundance. Each of the top 12 species was scored as to its vulnerability to increased minimum temperatures, drought, pest damage, species invasiveness, habitat specificity and storm damage. Scores for each risk factor were tallied to derive composite grades. Species with the lowest grades are projected to be most vulnerable to climate change impacts, and thus should no longer be planted in large numbers. Additionally, these indicators will be valuable in selecting tree species for trials that are presently well suited to more southerly climates, but due to climate change may be favorable for planting in the Central Valley. Likewise, these additions will serve as valuable tools in the planning of resilient urban forests to the effects of climate change in the California Central Valley and is adaptable to different climate zones, making it applicable to a wide audience outside of the Central Valley.