The assumption that tropical forest canopies offer protection from the effects of climate change is unfounded, says a researcher from the University of Cambridge.
Tropical forests - crucial strongholds for biodiversity - are under threat as temperatures rise in the world’s most diverse terrestrial ecosystems, the new study published this week in the journal Nature Climate Change reveals.
Conventional wisdom holds that the forest subcanopy and understorey – where direct sunlight is reduced – would be insulated from the worst climate change impacts by the shielding effect of the forest canopy.
However, in the study - which used a microclimate model to examine temperatures beneath the rainforest canopy across the global tropics between 2005 and 2019 - most of the world’s undisturbed tropical forests experienced climate conditions at least partially outside the range of historic conditions. Many areas had transitioned to almost entirely new temperature averages, but temperatures beneath the canopy in rainforests remained relatively stable. The wildlife beneath the canopy evolved within this narrow range of temperatures, leaving it poorly adapted to deal with temperatures outside this range.
Recent studies in largely undisturbed, or primary lowland tropical forests have found changes in species composition and significant declines in animal, insect, and plant populations. These changes are attributed to warming temperatures and are consistent with the findings of the new research.
“Tropical forests are the true powerhouses of global biodiversity, and the complex networks of species they contain underpin vast carbon stocks that help to mitigate climate change," said Professor David Edwards at the University of Cambridge’s Department of Plant Sciences, a co-author of the study. “A severe risk is that species are no longer able to survive within tropical forests as climate change intensifies, further exacerbating the global extinction crisis and degrading rainforest carbon stocks.”
Dr Alexander Lees, Reader in Biodiversity at Manchester Metropolitan University and a fellow co-author, added: “Our study challenges the prevailing notion that tropical forest canopies will mitigate climate change impacts and it helps us understand how to prioritise conservation of these key areas of biodiversity effectively.
“It is paramount that distant, wealth-related drivers of deforestation and degradation are addressed and that the future of those forests acting as climate refuges is secured by effecting legal protection, and by empowering indigenous communities.”
Lead author of the study, Dr Brittany Trew, conservation scientist for the Royal Society for the Protection of Birds, concluded: “Our research shows that climate change is already impacting vast areas of pristine tropical forest globally.
“To provide species with the best chance to adapt to these changes, these forests must be protected from additional human-induced threats.”
The study was made possible through a global collaboration that included researchers at Mountains of the Moon University, Uganda; Universidade Federal do Pará, Brazil; the Brazilian Agricultural Research Corporation and Universidad Nacional de San Antonio Abad del Cusco, Perú. It was funded by the National Science Foundation (NSF).
