Doctoral Dissertation Research: Fire-Driven Alternative States and Spatial Variability in Forest Resilience at a Dry Forest Ecotone

This doctoral dissertation project will investigate the drivers of forest gain and loss as well as tree regeneration and reburn severity in an area that is highly sensitive to environmental change - the dry forests on the eastern slopes of the Sierra Nevada Mountain of California. By examining vegetation change since 1950 at the lower margins of dry forest, and how these systems have changed in response to fires since 1986, the doctoral student will investigate the potential for fire-driven alternative states of forest and non-forest and how fine-scale spatial variability in topography and climate affect forest resilience. Given observed and predicted dry forest loss due to changes in temperature and increasing intensity and frequency of disturbances, determining where and when dry forests are likely to shift to an alternative state is critical to developing management plans to preserve forest cover. The results of this project will help guide management treatments such as prescribed fire, thinning and tree planting, by identifying portions of the landscape and conditions conducive to rapid vegetation change. This project will also enhance science training and education through participation of undergraduate students in field and laboratory work.

Future change in dry forest systems is likely to be abrupt and nonlinear, with severe disturbance potentially causing a conversion of forest to non-forest and positive feedbacks between disturbance and vegetation to some extent perpetuating the new mosaic of vegetation types. Ecotones, the boundary regions between ecosystems, are at the leading edge of change dynamics. This project will use aerial photographs to initially assess how the distribution of forest, woodland and steppe have changed at a forest/steppe ecotone since 1950, and relate shifts in distribution to topography, climate and disturbance history. Next, a network of field plots will be surveyed at the same sites in areas burned between 1987 and 2009 to evaluate post-fire tree regeneration and its drivers and the potential for fire-originated alternative vegetation states. Finally, remote sensing data on vegetation change, fire severity and disturbance history will be used to evaluate the potential for positive fire-vegetation feedbacks in areas burned twice since 1984 at the same ecotone. Insights gained from dry forest dynamics in the eastern Sierra Nevada through this project will be relevant to dry forest ecotones that are vulnerable to persistent fire-driven vegetation change elsewhere in the U.S. and around the world.