This study focuses on land use and land cover change and expansion of the Himalayan birch (Betula utilis D. Don) forest in the Nanda Devi Biosphere Reserve (NDBR) during a period of 23 years (1990–2013). It is based on two points of time, drawing on Landsat remote sensing data acquired from two different sensors: the Thematic Mapper (TM) in the year 1990 and the Operational Land Imager (OLI)/Thermal Infrared Sensor (TIRS) in 2013. The study revealed negative changes in vegetation cover, snow cover and river area. However, grasslands, open lands, agricultural lands and human settlements showed an increase in areas within the boundaries of NDBR. The results of the present study confirm a fair degree of variability in climate during the last few decades, leading to an increase in the density and expansion of pure and mixed Himalayan birch forest to the extent of 268 ha and 224 ha within the timberline ecotone (3200–4200 m Above sea level (Above sea level (ASL))). However, the timberline showed no advancement except for the increase in the number of Himalayan birch individuals within the existing boundaries of the timberline ecotone. The availability and abundance of seedlings/saplings beyond the treeline suggest great possibilities for the upward movement of the treeline in future. There is a need to explore the potential of new generation sensors with higher spatial or spectral resolution to accurately map even small patches of vegetation dynamics and produce accurate information on the differentiation between various species and vegetation types.