The Impact of Climate Change on Street Trees in California (Marsh Hall, 360 Prospect St)

September 14, 2017 - 12:00pm to 1:00pm

Joe McBride, UC Berkeley

Professor Emeritus of Landscape Architecture & Environmental Planning

Professor Emeritus of the Departments of Landscape Architecture & Environmental Planning and Environmental Science, Policy and Management, UC Berkeley. During his 44 year career at the University of California he taught courses in ecological analysis, forest ecology, urban forestry, and California Landscapes. He currently teaches Urban Ecology and hydrology at the University of Navarra in Pamplona, Spain. His research has focused on various aspects of urban forestry as well as studies of forest succession. The urban forest research includes studies of the effects of trees on air pollution in urban areas, transition of wildland forest to urban forests, the influence of biome characteristics on urban forests around the world, the reconstruction of urban forest destroyed by warfare, and the impact of climate change on street trees in California. McBride received a B.S. in forestry from the University of Montana and M.S. (Forestry) and Ph.D. (Botany) degrees from the University of California, Berkeley. Marsh Rotunda, 360 Prospect Street 12 p.m. - 1 p.m. Free and open to the public. Lunch provided.

The Impact of Climate Change on Street Trees in California

Climate change will alter the species composition of urban tree populations through a combination of modified precipitation regimes and increased temperatures. Likely changes in the composition of common street tree species in California were examined using the ‘space-for- time’ substitution method. Sixteen cities covering the climatic range of the state (“representative city”) were paired with a “warm city” counterpart, where the climate of today approximates the climate of the representative city in 2099. Of the 140 tree species found, as many as 83 species may be unsuitable for the future warmer climate in specific cities. This change is geographically non-uniform, with greater losses (up to 100% of common species unsuitable for future climate) found in cities away from the coast. In contrast, applying the “climate envelope” approach, i.e., assessing climate suitability of tree species from published sources based on the geographic distribution of a species, reduces the number of unsuitable species to as few as 14, although a more rigorous “professional judgment” approach that accounts for the substantial gaps in the “climate envelope” information results in 56 unsuitable tree species. The difference between the observed and estimated results (83 unsuitable species vs. 56) is likely caused by the climate envelope information insufficiently accounting for the irrigation needs of newly-planted street trees in the Mediterranean-type climates like California. The results of this study demonstrate the viability of the ‘space-for- time’ substitution method for evaluating possible climate change effects on urban trees, and suggest both an immediate need to re-evaluate the planting palette of street trees, and a long-term imperative to trial new tree species.