Global distribution and climatic controls of natural mountain treelines

Abstract

Mountain treelines are thought to be sensitive to climate change. However, how climate impacts mountain treelines is not yet fully understood as treelines may also be affected by other human activities. Here, we focus on “closed‐loop” mountain treelines (CLMT) that completely encircle a mountain and are less likely to have been influenced by human land‐use change. We detect a total length of ~916,425 km of CLMT across 243 mountain ranges globally and reveal a bimodal latitudinal distribution of treeline elevations with higher treeline elevations occurring at greater distances from the coast. Spatially, we find that temperature is the main climatic driver of treeline elevation in boreal and tropical regions, whereas precipitation drives CLMT position in temperate zones. Temporally, we show that 70% of CLMT have moved upward, with a mean shift rate of 1.2 m/year over the first decade of the 21st century. CLMT are shifting fastest in the tropics (mean of 3.1 m/year), but with greater variability. Our work provides a new mountain treeline database that isolates climate impacts from other anthropogenic pressures, and has important implications for biodiversity, natural resources, and ecosystem adaptation in a changing climate.

Upward‐moving mountain treelines: An indicator of changing climate

“…Research on the distribution of mountain treelines and treeline responses to climate change is critical in a changing world. He et al (2023) provided an exemplar for this field, as it not only develops a globally consistent way of detecting and monitoring closed‐loop treelines in mountains, but also complements previous studies on how natural treelines are responding to changes in climate (Camarero et al, 2021; Korner & Paulsen, 2004). In addition, the global closed‐loop mountain treeline database produced in this study provides a useful tool for biodiversity and carbon assessments, ecological modeling, and analyses of the adaptation of species to future climate change.…”

“…A recent work by He et al (2023) offers a new perspective to tackle these issues. This study proposed the “closed‐loop” mountain treelines (CLMTs), which refer to the treelines with a continuous band of tree cover that completely encircles a mountain.…”

“…Furthermore, this study comprehensively considered the main bioclimatic factors affecting the position of natural mountain treelines, including annual trends, seasonality, extreme of temperature and precipitation and other limiting environmental factors. Applying the gradient boosting decision tree model at a global and local scale, He et al (2023) revealed the distinctive controllers of CLMT over different regions: temperature is the primary climatic driver of treeline elevation in boreal and tropical regions, while precipitation dominates treeline elevation in temperate regions.…”

“…In addition to discussing the climatic factors that influence treeline dynamics, He et al (2023) provided insights into how treelines have shifted over the 21st century in response to changes in global climate patterns. Between 2000 and 2010, 70% of CLMT have moved upward (mean shift rate of 1.2 m/year), with the fastest rate in the tropics (mean of 3.1 m/year).…”

Climate change disrupts the seasonal coupling of plant and soil microbial nutrient cycling in an alpine ecosystem

“…Alpine ecosystems are experiencing numerous direct and indirect climate change impacts, which include huge reductions in snow cover and widespread shifts in vegetation, respectively (Beniston et al., 2018; He et al., 2023). Reduced snow cover and shifts in vegetation are among the most pronounced and globally widespread signals of climate change in alpine ecosystems (Gobiet et al., 2014; Kellner et al., 2023; Notarnicola, 2020; Pepin et al., 2022; Steinbauer et al., 2018; Zong et al., 2022), yet how they interactively modify key nutrient cycles is poorly understood (Classen et al., 2015), with the vast majority of studies focussing on single global change factors (Rillig et al., 2019).…”