Doctoral Dissertation Research: Mechanisms of shrubification in a changing Arctic

Arctic tundra is made up of a variety of plants, including mosses, grasses, flowering herbs, and woody shrubs, which guard vast quantities of underground carbon frozen in Arctic soils. As the Arctic warms, shrubs are replacing other plant species, altering the carbon cycle. The driving mechanisms and impacts of this shift on Arctic soil carbon remains unclear. This research explores the reasons behind this shift by testing three hypothesized mechanisms that may explain shrubs' competitive advantage in a warmer climate. These hypotheses include increased photosynthesis, greater response to nutrients made available by warming, and larger gains from longer growing seasons. The project employs mathematical models, field experiments, and surveys of shrubs across Alaskan tundra landscapes to test these mechanisms. This research will improve our understanding of vegetation changes and carbon cycling in the rapidly warming Arctic. Results will be shared via a public-facing interactive website and incorporated into K-12 and college courses. The goal of this research is to determine the mechanisms by which changing climate enables shrub dominance in heterogeneous Arctic ecosystems. The research approach combines trait-based models of competing tundra species informed with field experimental manipulations of temperature, nutrient availability, and snowmelt date. The full factorial experimental manipulation of these three environmental factors will allow researchers to untangle the relative contribution of the hypothesized mechanisms to shrubification. Since different mechanisms may be driving shrubification across vast and variable Arctic landscapes, researchers will conduct surveys of shrub populations and warming experiments across natural environmental gradients on the North Slope of Alaska. By clarifying mechanisms driving shrubification at local and landscape scales, this research will aid future efforts to represent Arctic shrubs accurately in Earth System Models and reduce uncertainties in climate change projections. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.