Minimal expansion of shrubland on the Tibetan Plateau over the past three decades

Abstract

Shrubland expansion is a globally occurring phenomenon under global change and has caused a wide range of ecological consequences. However, due to the visual similarity between shrubland and grassland, the accuracy of shrubland interpretation and its spatial distribution varies across different products, making shrub encroachment on the Tibetan Plateau (TP) uncertain. To address these challenges, we developed a phenology-based and pixel-wise method utilizing the Landsat, Sentinel-1, and Sentinel-2 image archives to map shrubland distribution from 1990 to 2022 across the TP. We also investigated the factors affecting shrubland distribution. Using the Random Forest (RF) model, we achieved moderate to high accuracies (Kappa ​= ​0.70–0.81) in predicting shrubland distributions, and we found that shrubland primarily occupies transitional zones between forest and grassland. In the southeast TP, solar radiation intensity is the dominant factor explaining the spatial distribution of shrubland, whereas in arid regions, water availability is the most important. From 1990 to 2022, the shrubland area slightly increased from 3.40% to 4.71%, with expansion showing a clustered pattern, mainly in the shaded aspects of arid regions. The shrubland identification method proposed here shows potential applicability in other areas with similar environmental conditions, such as arid landscapes or high-altitude ecosystems with pronounced seasonal vegetation dynamics. It also plays a crucial role in evaluating vegetation responses to climatic changes.