Vegetation browning trend progressively leading to forest degradation in eastern himalaya in response to climatic and anthropogenic drivers

Abstract

Vegetation is a major natural resource that plays an important role in maintaining ecological balance. Vegetation in the eastern Himalaya has experienced severe consequences owing to deforestation, fragmentation, land use land cover (LULC) conversion and climate change. Disturbances in vegetation have a close connection to browning trend because they modify the terrestrial ecosystems. Remote sensing derived vegetation indices and the availability of long-term satellite data allowed us to infer greening and browning tendencies across the Northeast Region (NER) of India. The present study has employed almost four decades (1982–2020) of satellite data (i.e. NDVI and LAI) and climate data (precipitation, soil moisture, temperature, solar radiation) to deduce the spatial pattern of greening and browning trends over major vegetation ecosystems, namely forest, grassland and cropland. Statistical metrics such as the Mann–Kendall test (τ) and the Theil–Sen median trend were computed to understand the greening and browning including vegetation degradation. The key findings exhibited that a noticeable large-scale greening trend of forests persisted in the first period (1982–2000) and switched to browning in the latest period (2000–2020). The statistically significant areas of browning trends over forest regions in NER was 5.6% which increased to 10.7–15.6%. The browning trends over grassland were more pronounced in the southernmost part of NER. Such changes were ascribed mostly to persistent warming and declining soil moisture. This was further exacerbated by human-induced LULC change. Over croplands, greening was prominent in Assam in the latest period, whilst other regions switched to browning. Trend analysis gives critical information on temperature-induced moisture stress leading to browning that might have potential implications for the forest, grassland and agriculture ecosystems. Specifically, the areas at Ziro Valley of Arunachal Pradesh showed high risk of forest degradation (i.e. 19% of the total forest area of 1816.54 km2), whereas areas around the Loktak Lake in Manipur exhibited high risk of cropland degradation. The states in the southernmost part of NER showed high risk of grassland degradation. Nearly 20–27% of the areas were identified as high risk of degradation. The study underscores the potential areas of NER where land management strategies need attention in the context of complex climatic factors along the side of anthropogenic influences.