A new study reveals that leaves of several agroforestry and forest species in Karnataka’s Western Ghats are regularly exposed to dangerously high temperatures, putting their health and the region’s economy at serious risk. Many species have already surpassed critical heat thresholds that impair photosynthesis and may cause irreversible damage.
Study Site in Karnataka Shows Early Signs of Thermal Stress
Researchers conducted a 4.5-month-long study in 2023 at Hosagadde village near Sirsi, a region frequently experiencing temperatures above 40°C. They monitored 13 agroforestry crops and 4 native forest species, using T₅₀ the temperature at which a leaf’s photosynthetic ability drops by 50% as a key stress marker. The findings show that many leaves are crossing this threshold far too often.
Crops Like Coffee, Cocoa, Lemon at Risk
Among agroforestry species, commercially valuable crops like cardamom, cinnamon, citrus, clove, cocoa, coffee, lemon, pepper, rambutan, and vanilla were studied. Cocoa, cinnamon, coffee, and lemon experienced leaf temperatures that could potentially cause damage, though exposures often lasted less than 10 minutes. Even such brief exposure, researchers noted, hints at the increasing stress tropical crops face under a warming climate.
Native Forest Trees Also Vulnerable
For native species such as kindal (Terminalia paniculata) and ironwood (Memecylon umbellatum), researchers observed episodes where leaf temperatures crossed safe physiological limits. The kindal, a deciduous tree, and ironwood, an evergreen species, may already be experiencing early effects of climate change.
Leaf Temperatures Soaring 10–12°C Above Air Temperature
At times of peak sunlight, leaf temperatures were found to be 10–12°C hotter than surrounding air, mainly due to direct solar exposure. This caused visible signs of damage in some plants, like blackened leaf tips. However, experts caution that factors like water stress or pests may also play a role.
The study highlights that while brief exposures may not immediately kill leaves, repeated stress could lower plant resilience. Many tropical species already operate close to their thermal limits. Future warming of 2°C–4°C could severely narrow the “thermal safety margins” the buffer between average leaf temperature and the T₅₀ threshold leaving crops with little room to survive extreme events.
What This Means for Farmers and Forests
The crops studied are central to Western Ghats’ agroforestry economy. Damage to cardamom, pepper, vanilla, and other valuable crops could have wide-reaching effects on both livelihoods and biodiversity. The study urges for targeted strategies to improve crop heat resilience and monitor real-world thermal thresholds, not just lab estimates.