Tree shade, temperature, and human health: evidence from invasive species-induced deforestation.
By providing shade and through evapotranspiration, trees and forests moderate temperatures, and thus, can indirectly affect human health, an economic variable of interest. In this paper, we measure the temperature and temperature-induced health effects of quasi-random tree cover loss caused by an invasive species, the emerald ash borer (EAB). We use monthly temperature data on the near-universe of US counties containing the invasive over 1995-2014 to estimate a temperature dose-response relationship. Then, dose-response results are integrated into a bioeconomic-health model to study the mortality and morbidity consequences of temperature fluctuations. We find that highest and mean monthly temperatures are increased by 0.28°F and 0.09°F, respectively, after EAB detection. There is also a 2.1% higher probability of experiencing at least one ≥90°F day per month after EAB. Bioeconomic model results suggest that an invasive-caused 10% loss of forest canopy leads to increases in mean temperature that result in a maximum of 0.12 per 100,000 additional annual deaths and a maximum of 10.0 per 100,000 additional annual emergency department visits. At peak impact, invasive-induced tree loss creates $1 million in annual mortality and morbidity temperature-related costs. Cumulative health costs of a 10% loss of tree canopy are $17.9 million over 25 years.