Some percentage of leaves from tropical forests are already exposed to such temperatures that prevent their normal functioning
A new study has pointed out new dangers of climate change — tropical trees could become so hot their leaves undergo necrosis. The tree leaves may die, leading to ‘mass leaf death’, or even stop conducting photosynthesis altogether.
The study Tropical forests are approaching critical level thresholds was published in Nature journal on August 23.
The mean temperatures are high in tropical forests and their day and seasonal variations are comparatively small, the study said. The average temperatures have increased by 0.5 degrees Celsius per decade in some tropical regions.
Read more: El Niño effect: Even in drought-tolerant forests, seedlings more likely to die
Even small changes in the temperature brought on by the warming planet can have great impact on the plant species, it added.
Weather phenomenon like climate pattern El Nino are becoming more pronounced, it said. Tropical forests may experience reduced transpirational cooling (movement of water through a plant and out of its leaves and other aerial parts into the atmosphere). This can expose them to destructive temperatures.
If individual leaf temperatures increased over 46.7 degrees Celsius, the leaves stopped conducting photosynthesis, showed calculations made by researchers using multiple models. If prolonged, the leaves died.
A small percentage — 0.01 per cent — of all leaves in the tropical forests are already exposed to such temperatures that prevent their normal functioning, the paper found.
The mean canopy temperature can increase by a maximum of 4.4°C either due to a drop in soil moisture or from an increase in dead leaves, as the models further showed.
Read more: Hunting has affected more than half of tropical forests: Study
“Our work suggests that a tipping point in metabolic function in tropical forests could occur with 3.9°C with a variable of 0.5°C of additional warming, which is more than expected for tropical forests under Representative Concentration Pathways or RCP 2.6, but less than RCP 6 or 8.5,” it noted.
According to Intergovernmental Panel on Climate Change, RCP 2.6 scenario is when carbon emissions start declining by 2020, while RCP 6 is a greenhouse gases stabilisation scenario in which total radiative forcing is stabilised after 2100 by deploying a range of technologies and strategies.
If the global temperatures increase by 3.9 degrees Celsius, these forests may collapse undergoing mass leaf damage, the study further stated. The scenario would occur in case of RCP 8.5 considering that no steps are taken to mitigate the impacts of climate change.
These leaves may not undergo irreversible damage until prolonged exposure to heat that may lead to desiccation, the scientists said. But if the situation persists, the entire tree could die as it would not be able to regrow the leaves. Tropical trees may use non-structural carbohydrate reserves to revive the leaves in later years, it added.
However, these possibilities are highly uncertain. It is because if the tree loses its natural abilities to reflush leaves and fails to reduce evaporative cooling, in which case the tree may die.
The models indicate that tree death could come sooner than expected due to the combined effects of mechanisms and their interactions such as “carbon starvation, hydraulic limitation and fire, among others.”
Even at lower temperatures or partial canopy death can negatively impact the capacity of carbon dioxide uptake feedbacks that could result in accelerating climate change impacts. Temperature range between 2 and 8.1°C, where 2 being the lowest and latter the highest, results in leaf death, the study showed.
Deforestation and fragmentation of forests can increase or destabilise local temperatures, the paper warned. The effects of climate change combined by local deforestation may already be pushing the hottest tropical forest such as the southeast Amazon regions towards critical thermal threshold, it added.
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Tropical forests may experience reduced transpirational cooling that can expose them to destructive temperatures. Photo: iStock.png)
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