Unraveling meteorological drivers of leaf phenology in the Western Ghats, India

Abstract

Phenology, the study of periodic biological events in relation to biotic and abiotic factors, is a critical indicator of ecosystem dynamics, influencing carbon cycling, vegetation productivity, and ecosystem responses to climate change. The current study investigates phenological dynamics and net primary productivity (NPP) trends across tropical forests in the Central Western Ghats, India, emphasizing the role of climatic factors such as temperature, relative humidity, soil moisture, precipitation, and photosynthetically active radiation (PAR). Using satellite-derived MODIS NDVI data and near-surface remote sensing data from PhenoCam, the study shows a significant delay in leaf flushing (7 days/decade) and advancement of leaf fall (13 days/decade) in tropical semi-evergreen forests, which experience a shortened length of seasons by 17 days/ decade. However, the dry deciduous and thorn forests show an increasing season length of 7 days/decade. The climatic variables, such as minimum temperature and relative humidity, drive leaf flushing, while maximum temperature and PAR control leaf senescence in these forest types during a short period of preseason length. The study also shows a closer alignment between MODIS and PhenoCam-derived phenological metrics for the tropical semi-evergreen forests. A declining NPP trend is observed in semi-evergreen and moist deciduous forests (−4.0 × 10⁻³ kg C/m². year), contrasting with increases in dry deciduous and thorn forests, with annual temperature significantly controlling NPP trends (r ∼ -0.6, p = 0.001). Additionally, soil moisture shows a positive correlation with NPP in dry forest areas. This is the first comprehensive study from the Central Western Ghats that integrates satellite and near-surface phenological observations with a wide range of climatic variables to examine forest phenology and productivity. The findings offer novel insights into the climate sensitivity of tropical forest ecosystems and provide a valuable scientific basis for climate-resilient forest conservation and management strategies.