Mapping forest phenological shift in Nilgiri Biosphere Reserve, Western Ghats: Response to climate change

In the present study, the spatiotemporal alterations in phenological metrics were analyzed in different forest types of Nilgiri Biosphere Reserve (NBR), Western Ghats, India with special reference to the impacts of changing climate on the forest phenology over two-phase periods (Phase 1: 2001-2010 and Phase 2: 2011-2020). Three phenological measures including the start/end/ length of the season (SOS/EOS/LOS) were obtained using 16 days of MODIS Enhanced Vegetation Index (EVI) dataset over the two decades. The study exhibited a gradual delay in SOS during phase 1, and an advancing SOS during phase 2 in the tropical forests of NBR. Delayed EOS was observed in all forest types in NBR barring Moist Deciduous Forests (MDF) during phase 1, while opposite trend of advancing EOS was observed in deciduous forests (MDF and DDF: Dry Deciduous Forests), but delayed EOS was observed in evergreen forests (SEF: Semi Evergreen Forests and WEF: Wet Evergreen Forests) during phase 2. These variations in forest phenology are linked with an increase in annual mean temperature (0.01 degrees C year-1) along with a decrease in annual mean precipitation (3.97 mm year-1) during 1950-2018 as observed using IMD-based meteorological datasets. The results highlighted reduction in the total LOS with a delayed SOS and advanced EOS in NBR, which were prevalent during phase 1 conversely to phase 2 due to the varied intensity of changes in climatic conditions. However, disaggregating decade-long intervals into 5year segments enables a finer resolution analysis of phenological trends. The study contributes to the development of long-term strategies for forest ecosystem restoration under the influence of global climate change by providing an insightful understanding of the non-systematic shifts in forest phenology attributed by rising warming impacts and erratic precipitation patterns.