Urban greenspaces promote warmer soil surface temperatures in a snow-covered city

Abstract

The complex ecological and socioeconomic interactions that exist in urban areas create novel abiotic environments and novel ecosystems. Microclimates in urban areas have been studied during the summer months; however, climate change is also increasing the frequency of extreme cold outbreaks during winter. Quantifying microclimatic variation in soil surface temperatures, the level at which most plants and animals persist, can help predict the effects of climate on biota in temperate and high-latitude cities. Using fine-scale temporal and spatial data, we investigated how air temperature and snow characteristics interact with land cover and land use to drive variation in soil surface temperatures in greenspaces throughout a mid-sized city in the United States. We found that snow reduced variability in soil surface temperatures, which remained around 0 °C when snow depth was greater than or equal to 20 cm, with air temperature and snow depth interacting strongly to drive this effect. Tree cover promoted warmer soil surface temperatures regardless of snow cover, with relatively warmer soil surface temperatures in natural areas and residential yards compared to those in public landscaped areas (e.g., managed parks). In fact, under extremely low air temperatures (∼−30 °C), the warming effect of urban forests reached 4 °C, which provided substantial buffering from extreme cold. Our results highlight the potential for urban greenspaces with trees and snow to serve as refugia for organisms in the winter, and subsequently preserve essential ecosystem services provided by urban biodiversity. Consequently, urban planners should aim to maximize tree cover where possible and supplement greenspaces with vegetation (i.e. shrubs and leaf litter) that promotes snow retention during the winter.