Spatio-temporal analysis of trends in seasonal vegetation productivity across Uttarakhand, Indian Himalayas, 2000-2014

Himalayan mountain system in the Indian sub-continent are among the most ecologically sensitive environments and are also a repository of biodiversity, water and ecosystem services. Over the last two decades, land transformation related to exploitative land uses is among the main drivers of changing vegetation cover and productivity in western Himalayas. In a region where field based research is challenging due to heterogenous relief and high altitude, quantifying changes in vegetation photosynthetic activity using remote sensing can provide essential information regarding trends in vegetation cover and its linkages with anthropogenic impacts. We conducted seasonal trend analysis (STA) on MODIS NDVI time-series data (2000-2014) over Uttarakhand Himalayas and examined spatio-temporal patterns in vegetation trends and its association with altitudinal gradient and land use land cover (LULC) dynamics. In STA the first step determines the annual mean and seasonal NDVI patterns and the second step analyzes the non-parametric trend in magnitude and timing of the annual mean and seasonal NDVI cycle. To provide insights on the role of changing land use to detected changes in vegetation trend, we linked MODIS derived trends to land transformation processes using multi-temporal high spatial resolution imagery in Google Earth (GE). In total 3286.82 km(2) (6.9% vegetated area of Uttarakhand) showed significant trend (p < 0.01) in mean annual greenness. While areas <800 m elevation showed dominant negative trend in mean annual greenness (browning)), those between 800 and 1600 m showed mostly positive trend (greening) and majority of areas >1600 m were characterized by negative trend in mean annual greenness. Majority of intensively cultivated irrigated croplands in the Himalayan foothills as well as areas around growing urban centers showed widespread browning, which was contrastingly different from rainfed cultivation areas that showed dominant greening trend. Browning trend was observed to be consistent with increasing altitude, particularly in closed needle leaf forests and alpine shrublands, except areas where human impacts has led to more mixed patterns. Trends in the annual seasonal timing of NDVI indicated an earlier green-up for most parts of the Uttarakhand Himalayas. These results highlight fine scale spatial variations in seasonal vegetation trends and are in partial agreement with previous studies that report only increasing brownness detected at broader scale using much coarser spatial resolution time-series. (C) 2014 Elsevier Ltd. All rights reserved.