Jennifer E. Davison
When we describe a natural environment in terms of the plants we see, it commonly includes some description of the amount, size and distribution of trees and shrubs: the labels "grasslands", "shrublands", "woodlands" and "forests" are implicit descriptions of the degree of woody plants in those communities. In fact, most of the Earth's terrestrial ecosystems can be seen as existing along a gradient of woody plant cover. Woody plants modify the surrounding ecosystem in many ways through their physical and biological presence, affecting nutrient and hydrological cycles, the carbon balance, and biological diversity.
The Sky Islands, isolated mountain ranges in the southwestern USA, are particularly sensitive and important examples of grassland-forest gradients: highly biologically diverse with vegetation communities from desert grasslands to coniferous forests along their steep slopes. With unanticipated climate change effects like wide-scale tree death such as that seen on a regional scale in the Southwest in 2002, there is an urgent need to detect, predict and manage the response to disturbances like drought and wildfire, not only of Sky Islands but all ecosystems along the theoretical grassland-forest continuum. Additionally, because Sky Islands consist of compressed vegetation communities with many species at the edge of their environmental ranges, these systems could be valuable as "barometers" of climate change impacts. Yet, though research often sheds light on particular ecosystems and their bioclimatic characteristics, systematic patterns along woody plant gradients in response to climatic trends and extreme events are not well known.
The aim of my research is to develop and improve detection, diagnosis and explanation of disturbance along gradients of woody plant cover. Focusing on Sky Islands in the southwestern USA, I use remotely sensed, modeled and field-based data to explore vegetation productivity and growth cycles (phenology) and how these dynamics respond to drought and drought-induced plant mortality. I hope to provide insights into the grassland-forest continuum as a concept, to increase understanding of varying phenological responses along the woody plant gradient with respect to drought, and to shed light on Sky Islands as barometers of change due to climate and other drivers.
