Urban forests can help connect city dwellers with nature and mitigate effects of climate change. Despite providing shade, dissipating heat through evapotranspiration and storing carbon through photosynthesis, urban trees and shrubs themselves, however, may be under risk to climate change.
In this study, researchers analysed the potential impacts of future climate change on 3,000+ tree and shrub species in 164 cities across 78 countries based on the Global Urban Tree Inventory. For these, the authors collected occurrence records from GBIF and sPlotOpen (an open-access, global dataset of vegetation plots), and characterized the climatic niches of each species based on data on temperature and precipitation.
For each city, they calculated the potential exposure to climate change as the difference between future and current climate. Then, for each species-by-city combination, they calculated a safety margin, indicating the tolerance to climate conditions exceeding upper or lower limits. Finally, based on cities' intrisic exposure and species' safety margins, the authors derived an overall risk to climate change.
Their analysis predicted the highest exposures to climate change in Helsinki (Finland), Winnipeg (Canada) and Minneapolis (USA). Overall, up to 65 per cent of species were currently exceeding their margins. In Barcelona (Spain), Niamey (Niger) and Singapore, this applied to 100 per cent of species present.
The authors estimated that by 2050, up to 76 per cent of all urban trees and shrubs would be at risk. The proportion of species at risk for cities tended to increase towards the equator. They found the highest risks in cities projected to have warmer and drier climates, in countries with low resilience to climate change, highlighting Pretoria (South Africa) and New Delhi (India) as examples.