Forest structure and composition alleviate human thermal stress

Abstract

Current climate change aggravates human health hazards posed by heat stress. Forests can locally mitigate this by acting as strong thermal buffers, yet potential mediation by forest ecological characteristics remains underexplored. We report over 14 months of hourly microclimate data from 131 forest plots across four European countries and compare these to open-field controls using physiologically equivalent temperature (PET) to reflect human thermal perception. Forests slightly tempered cold extremes, but the strongest buffering occurred under very hot conditions (PET >35°C), where forests reduced strong to extreme heat stress day occurrence by 84.1%. Mature forests cooled the microclimate by 12.1 to 14.5°C PET under, respectively, strong and extreme heat stress conditions. Even young plantations reduced those conditions by 10°C PET. Forest structure strongly modulated the buffering capacity, which was enhanced by increasing stand density, canopy height and canopy closure. Tree species composition had a more modest yet significant influence: that is, strongly shadecasting, small-leaved evergreen species amplified cooling. Tree diversity had little direct influences, though indirect effects through stand structure remain possible.Forests in general, both young and mature, are thus strong thermal stress reducers, but their cooling potential can be even further amplified, given targeted (urban) forest management that considers these new insights.

Tree diversity increases forest temperature buffering

“…1), tree diversity-enhanced temperature buffering may impact forest biodiversity under global warming by reducing the thermophilization of below-canopy communities 7,15,16 . Finally, forest temperature buffering also alleviates heat stress for humans, and our findings indicate that tree species richness may amplify this effect far stronger than previously reported 32 .…”

“…There is ample evidence that forests buffer temperature extremes 2,3,9 and that species identities matter for temperature buffering 4,25 , but the role of tree diversity has largely remained hidden. The few former studies on the role of tree species composition for temperature buffering reported predominantly non-significant effects of species richness 25,32,34 . Positive effects were rare and only found for specific mixtures 4 .…”

Plant diversity stabilizes soil temperature

“…functioning. A few recent studies have shown that plants can buffer air temperature inside forests [12][13][14][15] . However, whether plants can contribute to buffering soil temperature is still unclear.…”

“…Thus, mitigating the effects of extreme weather events on soil temperature fluctuations can contribute to stable ecosystem functioning. A few recent studies have shown that plants can buffer air temperature inside forests 12–15 . However, whether plants can contribute to buffering soil temperature is still unclear.…”

Preface: Celebrating the 100th anniversary of chemical sciences in Nanjing University

“…Fortunately, we know that heat stress can be buffered, in part, by vegetation in cities 24 . Urban green spaces, and especially urban forests, have proven an effective means through which to ameliorate heat stress through shading and transpirational cooling [25][26][27] . The buffering effect of urban green space is influenced by its area relative to the area of the city and its spatial configuration 28,29 .…”