Extensive drought-induced forest mortality has recently been documented worldwide, is likely to be exacerbated by future climate change, and holds large ecological consequences. Yet the pathways through which meteorological drought causes plant mortality are poorly understood. As the most widely distributed tree in North America and the only major deciduous alpine tree in the Rocky Mountains, trembling aspen (Populus tremuloides) is a critical component of ecosystem diversity. In the past decade, an estimated 20% of trembling aspen trees throughout the Rocky Mountains have experienced rapid and severe drought-linked mortality termed Sudden Aspen Decline or SAD. Using stable isotope analysis of aspen xylem water, I investigated aspen water source use throughout the growing season and over a variety of environmental conditions in southwest Colorado in order to determine how tree ecophysiology interacts with drought seasonality and site hydrology to result in plant water stress. I also explored water source use by co-occuring understory and tree species.
Results/Conclusions
Isotopic analysis indicates that aspen trees transpire primarily water from shallow soil layers regardless of location and moisture availability. There also appears to be no partitioning of water resources between plant functional types in aspen communities. This dependence on shallow soil moisture and potential competition for water between aspens and co-occuring species yields insights into the drought characteristics that are most likely to cause water stress in aspens.