Examining Species Diversity and Urban Forest Resilience in the Milwaukee, Wisconsin (USA) Metropolitan Area

Abstract

Abstract Potential impacts from climate change and other disturbances expedite the need to address vulnerabilities of urban forests. Low species diversity is a contributor to high urban forest vulnerability, and this study examined 40 public and private tree inventories in the metropolitan area of Milwaukee, Wisconsin, USA. Applying an established vulnerability framework, this study helps to identify the current and future resilience of the urban forest in the face of climate change and other urban forest threats. A Milwaukee metropolitan area tree inventory was compiled and includes 439,974 trees. This inventory then was assessed under 2 climate change models through the end of the century (2070 to 2099). It also was assessed for species diversity under multiple diameter classes, and the Shannon Diversity Index was used to determine correlations between tree size and diversity. The resulting data analysis revealed a poorly diversified urban tree canopy in the Milwaukee metropolitan area. However, when looking at tree size and diversity, diversity increased as tree diameters decreased. Additional analysis revealed that under a low climate change scenario (RCP 4.5), only 9.5% of the overall inventory was within the moderate, moderate-high, or high vulnerability categories through the end of the century. Under a high climate change scenario (RCP 8.5), 55.52% of the inventory fell within those same vulnerability categories. Diameter class did not have a significant impact on vulnerability under either climate change scenario. This data can help inform urban forestry practitioners during species selection for planting trees in their communities.