Identification and spatial pattern analysis of alpine timberline by remote sensing methods in Yarlung Zangpo Grand Canyon

As an important ecotone, the alpine timberline is the boundary between closed-canopy montane forest and alpine vegetation, and is highly sensitive to global and regional climate changes. We provided a way to identify and extract the alpine timberline in Yarlung Zangpo Grand Canyon Nature Reserve by using remote sensing data and spatial analysis based on land use/land cover classification and NDVI distribution characteristics. Combining DEM data, the influence of slope and aspect on the distribution of alpine timberline was explored. The results showed that the alpine timberline in Yarlung Zangpo Grand Canyon is transitional timberline, with the upper boundary approximately distributed at the elevation of 3422-4373 m, the lower boundary at approximately 3270-4164 m, with a width of about 110-280 m. Alpine timberline was mainly distributed on steep and very steep slopes ranging from 25° to 45°. The maximum elevation of both the upper and lower boundaries occurred on steep slopes. The distribution of alpine timberline varies with aspects, with sunny slopes having a higher boundary than shady slopes.