Response of aspen to a warming climate along a latitudinal gradient in the Rocky Mountains, USA

The 21st century's warming climate threatens aspen (Populus tremuloides) growth in the southern Rocky Mountains (western US), endangering ecosystem diversity, functionality, and associated services. This study linked aspen growth with temperature and moisture variations, assessing how warmer climates and seasonal changes affect ring widths. Sampling 211 aspen trees from 12 latitudinally distributed sites, we compiled three regional aspen chronologies spanning 1913 to 2018. We investigated climate-growth associations using correlation and modeling (climwin) techniques. Results revealed that aspen at the trailing southern edge of the Rocky Mountains are vulnerable to drought, where elevated temperatures and diminished precipitation emerge as primary factors contributing to their reduced growth. In contrast, aspens in the northern region of the gradient exhibited a positive growth response to rising temperatures, potentially linked to the alleviation of growth-limiting cold temperatures. However, while pre-2000s droughts increased growth, recent droughts elicited growth reductions in the North; suggesting that with continued warming, northern populations will increasingly face sensitivity to droughts akin to their southern counterparts. These findings emphasize the increased vulnerability of southern Rocky Mountain aspen populations to climate change-induced growth constraints, particularly in the anticipated warmer and drier conditions of the 21st century. This study is crucial to understanding aspen responses to climate fluctuations in the region.