Trends of forest phenology studies in India-challenges and opportunity for satellite remote sensing and near surface sensors

Phenology, for being pulse of the ecosystem, elucidates the complex relationship between climate and vegetation, serving as a vital indicator of climate change. India, a biodiversity hotspot, has forests classified into 5 major groups, 16 subgroups, and 255 subtypes based on climatic, edaphic, and successional variations, displaying varying phenological traits. Recent advancements in technology have revolutionized our ability to collect valuable data across various spatial and ecological scales. Despite the abundant observational data capturing phenological changes at various scales, remote sensing remains a relatively less explored tool for operational forest phenology monitoring in Indian forest ecosystems. This comprehensive review explores the latent potential of long-term satellite remote sensing data supported with near surface sensor system networks to reveal complex patterns of phenological dynamics within a spectrum of diverse forest types in India. We found that, majority of the research has predominantly focused on field-based observations limited to moist and dry tropical forests, followed by montane temperate and subtropical forests driven by their ecological importance, higher accessibility, and their sensitivity to climate change impacts. Through the utilization of advanced satellite sensors (e.g., MODIS, Landsat, and Sentinel) thorough investigations have successfully examined the dynamics of vegetation in forest phenological studies. Looking ahead, integrated studies with diverse monitoring methods are crucial for upscaling phenological observations robustly. These advances are necessary to precisely quantify the impacts of a changing world on forest phenology.