Global Alpine Treeline Ecotone Dynamics (1985-2020)

Keywords: Alpine treeline ecotone, Vegetation dynamics, Elevational gradient, Mountain ecosystem, LANDSAT
Abstract Type: Paper Abstract

Abstract

In mountainous regions worldwide, tree species do not persist above certain elevations due to short growing seasons and thus yield the terrain to short-stature vegetation, which causes the “Alpine Treeline Ecotone (ATE)”, a critical ecological transition zone from montane forests to alpine tundra areas. Under the recent human-mediated climate change, upper regions in the mountains often experience more rapid variations in temperature than adjacent low-lying areas, contributing to weaker temperature gradients in ATEs. A better understanding of how primary productivity has varied in the world’s ATEs over the past decades under the potentially more homogenized temperature is crucial for predicting the consequences of environmental change on mountain ecosystem functioning. Here, we leveraged a global climatology product and other pertinent environmental factors (e.g., elevation, hydrology, landforms, and land cover) to construct approximately 2.1 million elevational transects in the identified ATEs worldwide. Based on the 30-m annual maximum “greenness” indices derived from the LANDSAT archive during 1985-2020, we observed that 96.6% of the world’s ATEs were “greening” during the study period. Regarding primary productivity, 52.6% of the transects became more homogenized along the elevational gradient, primarily in boreal regions. Our findings indicate that the responses of ATEs to the changing climate vary by region and elevation, which can help to improve projections of future vegetation dynamics in mountain ecosystems worldwide.