CMG Landscape Designer, Kate Lenahan, traveled to San Luis Obispo September 26-28 to attend the 2019 California Urban Forests Conference. This year’s conference discussed the impacts of climate change on urban forests and the urban lumber industry– presenting current research on climate-appropriate tree selection, urban canopy management, and wood reuse in California. As CMG works to capture more carbon, understanding what species and planting strategies will be most climate adaptive and carbon positive will be key to balancing our projects’ emissions in the future.
Day 1 of the conference focused on climate change and the urban forest, examining the effects of projected shifts in heat, drought, and accompanying pests on trees in California’s cities, as well as the communities that most need them. Presentations by Drs. Matt Ritter and Igor Lacan underscored that careful tree selection today will be critical to maintaining a healthy urban forest under increasingly stressful conditions. Lacan and McBride’s work on space-for-time substitution outlines a framework to project climate and species shifts in California cities, using the canopies of warmer cities to anticipate which common species will not tolerate future conditions.1 The loss of trees will be greatest inland, where temperatures are projected to rise more than on the coast. Planting urban forests with greater biodiversity now, argues Dr. Ritter, may protect against their decline over time. Out of 60,065 tree species in the world, only approximately 1.7% of them are selected for urban forests.2 If many of California’s common urban tree species will no longer be suitable in a warmer climate, there’s a good chance that others–represented in this uncaptured biodiversity–will be successful. “Common garden” studies through UC Davis are ongoing to test urban-appropriate trees for California’s future cities.
Day 2 focused on the urban lumber industry, picking up where Friday’s foresters left off, addressing the end of life uses of our cities’ trees. Most often, removed trees are trucked to landfills or ground for mulch. Although mulch releases some carbon to the soil, most carbon stored in mulch wood is eventually emitted back tot he atmoshere as it decomposes. Dr. Sam Sherrill explained that every year, and estimated back to the atmosphere as it decomposes. Dr. Sam Sherrill explained that every year, as estimated 3 to 4 billion board feet of wood are disposed in these ways3, representing approximately 7.1-9.5 million tons of carbon. Urban lumber offers an alternative; recycling trees as hardwood products like architectural finishes and site elements could retain a significant store of carbon, stored as long as these products exist. In 2017, buildings accounted for 44% of San Francisco’s GHG emissions, or 2.2 million tons4 (for comparison, the average car emits 5.1 tons of carbon dioxide annually). As the California urban lumber industry organizes and develops standards, it could become a powerful tool for designers of the built environment to offset construction impacts.
- McBride, Joe, and Lacan, Igor. “The impact of climate-change induced temperature increases on the suitability of street tree species in California (USA) cities.” Urban Forestry & Urban Greening, 2018. 34, 348-356. https://www.sciencedirect.com/science/article/pii/S1618866718300013
- Ritter, Matt. “California Tree Selection: Factors to Consider in an Era of Climate Chaos and Decreasing Diversity.” 2019 California Urban Forests Conference, 27 Sept. 2019, Ludwick Community Center, San Luis Obispo, CA. Conference Presentation.
- Sherrill, Sam. “Atmospheric Carbon Dioxide and Carbon Storage in Wood Products.” 2019 California Urban Forests Conference, 27 Sept. 2019, Ludwick Community Center, San Luis Obispo, CA. Conference Presentation.
- San Francisco Department of the Environment. “San Francisco’s Carbon Footprint.” Accessed 7 Oct. 2019. https://sfenvironment.org/carbonfootprint