Tropical forest biodiversity at high risk from climate change due to temperature change under canopies: Study 

Humid tropical forests are worldwide hotspots for terrestrial biodiversity but climate change-induced warming is affecting how they operate, says a new study

A new study has found significant shifts in below-canopy climate conditions in a considerable area of tropical forests around the world. The study compared how overall temperature change across the past 30 years affected the degree of below-canopy temperature in these forests. This included globally important national parks, Indigenous reserves and large tracts of ecologically unfragmented areas.

The study said that changes in species composition and significant declines in animal, insect and plant populations have been observed in tropical lands. According to the study, these changes are attributed to warming temperatures. For example,  the abundance of terrestrial and near-ground insectivore bird species has declined in primary tropical forests in the Brazilian Amazon since the 1980s. The evidence, as per the study, said that these species respond to warming by closely tracking cooler microclimates.

As per the researchers, the idea that tropical forest canopies lessen the severity of climate change impacts has been called into question due to their analysis of changes in below-canopy climatic conditions throughout the world. 

This is because the majority of species live within or below the canopy, providing them with a buffer against extreme temperatures. Additionally, under forest canopies, direct sunlight is strongly reduced and evapotranspirative cooling is increased, which dampens temperature fluctuations compared with open habitats and resulting in cooler below-canopy maximum temperatures, warmer minimum.

Moreover, novel climates—those with no recent historic analogues—are predicted to appear first in the tropics and subtropics, they added.  

The study modelled the hourly below-canopy climate conditions of 3,00,000 tropical forest locations globally between 1990 and 2019. The study showed that recent small increases in below-canopy temperature (<1 °C) have led to highly novel temperature regimes across most of the tropics.

Why are tropical forests important?

Over 62% of vertebrate species and over 75% of flowering plant species are found in tropical forests, making them the most diverse terrestrial ecosystems in the world, according to the study.

Humid tropical forests are worldwide hotspots for terrestrial biodiversity, impacting climate regimes, terrestrial carbon cycles, and species conservation. However, clearing, selective logging, wildfires, and increasingly frequent extreme weather events—like blowdowns and droughts—caused by climate change are eroding the ecological integrity of tropical forests worldwide. 

Impact on forest ecosystems

The study noted evolutionary history means that tropical forest organisms evolved under a narrower range of climate conditions than extratropical biota and can therefore tolerate a smaller margin of warming above their most favourable thermal conditions. 

As a result of lower natural climate variability, many tropical forest species have narrow realised climate niches and are not pre-adapted to warmer conditions.

Need for tropical forest restoration

According to the study, initiatives for forest restoration should focus on enhancing the interior area, total size, and connectedness of fragmented refugia—areas where a population of organisms can endure a time of unfavourable conditions. To further prevent additional harm to the world’s tropical forest ecosystems, it is also essential to reduce carbon emissions globally and restore highly threatened forests. 

The study also identified areas where temperature changes have been low despite ongoing climatic change. Although many are highly fragmented and dispersed across continents, especially in Africa, these tropical forests are the best candidates to act as climate refugia and are crucial to conservation efforts. Their usefulness as refugia will depend on their connectivity to areas with unfavourable climates, enabling species range-shifts.

It is critical to address the drivers of deforestation and degradation and that intact candidate refugia are urgently and vigorously protected, via legal protection, carbon payments or empowering indigenous communities, the study said. 

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