Rising temperatures will make Miami’s street life even more exotic

Species in humid, tropical regions frequently experience dangerously high heat. The danger of high temperatures is especially pronounced in cities due to the urban heat island effect. Trees can greatly reduce surface temperatures and mitigate the urban heat island effect through evapotranspiration and by reflecting solar radiation before it is absorbed by impervious surfaces. However, trees may also be physiologically susceptible to the effects of climate change as high temperatures exceed their physiological limits. In this study, we assessed how the urban tree community in subtropical Miami (Florida, USA) will be impacted by climate warming and how impacts will differ between native and exotic tree species. We calculated the thermal safety margin (TSM) in Miami for each of 235 tree species as the difference between the maximum temperature experienced by a species within its range and the current and future (2100) projected maximum temperature in the city. We also combined TSMs, a metric of resilience to heat, with each species’ drought, wind, and salt tolerance to identify species that are resilient to multiple relevant stressors. We found that by 2100 Miami will be too hot for 16–41 % of the tree species currently planted in the city, depending on the climate change scenario. Native tree species will be disproportionately impacted compared to exotics, likely because most exotic species originate in the tropics, whereas most species native to Miami are primarily subtropical or temperate. The species that are more resilient to multiple stressors include mostly native species, several of which are ideal shade trees. Urban greening initiatives should carefully consider tree plantings to optimize the long-term health of urban tree communities and the services that they can provide to cities in the future.