Spatiotemporal trends of drought in the forest-shrubland ecotone of southern Wyoming

Little attention has been given to the effect of top down climatic controls on the condition of forest across the region, with respect to both dry periods and extreme drought years. In collaboration with Patrick Anderson and Jason Sibold, we assessed the relationship between recent satellite imagery and the condition of vegetation on the ground; then backcast the relationship over the last thirty years to determine when and where change occurred. We hypothesized the long-term trajectory of forest condition could be used to highlight areas of forest that are resistant, persistent or vulnerable to severe drought. Our findings identify spatially explicit patterns of long-term trends anchored with ground based evidence which provides a long-term perspective for the resource management of this area. More information on our work modeling forest cover can be found here; more information on the trend analysis can be found here; more information on linking field and spaced-based observations can be found here.

A vulnerable plot (negative trend) with high levels of plant mortality due to Douglas-fir beetle, an indirect result of drought (Assal et al. 2016).
A vulnerable plot (negative trend) with high levels of plant mortality due to Douglas-fir beetle, an indirect result of drought (Assal et al. 2016).

Ecological consequences of multiple forest disturbances in Glacier National Park

Fire following the recent mountain pine beetle outbreak (~1996-2006) is an area of active research, but few studies have analyzed the ecological legacies of historic events. I am collaborating with Jason Sibold to determine if the severity of the 1970s mountain pine beetle outbreak had a measurable influence on burn severity in wildfires in the ensuing decades. We overcame an initial challenge (i.e. wildfire removed some of the evidence from the landscape) using multiple lines of evidence to model forest canopy mortality as a proxy for beetle outbreak severity. We are using this information coupled with additional explanatory variables to untangle the influence of beetle severity on burn severity. The long-term perspective of this retrospective study is relevant to the future of our forests, as much of the current landscape impacted by the recent beetle outbreak is maturing. More information on modeling the severity of the 1970s beetle outbreak can be found here.

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Dark gray areas in the color-infrared photo (left) indicate high forest mortality which corresponds to severe modeled beetle severity (right) (Assal et al. 2014).

Fire effects in Andean Araucaria-Nothofagus Forest, Tolhuaca National Park

 Fire is the most important disturbance influencing Araucaria-Nothofagus forest of south-central Chile and there is concern that increased ignition (human or natural sources) may strengthen a positive feedback, making recently burned areas highly prone to subsequent fire. In collaboration with Mauro Gonzalez and Jason Sibold, we designed a field study to measure regeneration and retrospectively calibrate modeled burn severity (of a 2002 fire) from satellite data. Our findings accurately capture the steep burn severity gradient, which has strong implications on post-fire regeneration. However, a 2015 fire reburned the majority of the study area. We will investigate the potential for a site type conversion from forest to bamboo thickets and hope to improve our understanding of the complex interaction between fire and land-use changes in Andean forests. More information on our research in Tolhuaca National Park can be found here.

Comparison of 2002 and 2015 fire in Tolhuaca National Park.
Approximate extent of burned area of 2002 and 2015 fires in Tolhuaca National Park.


research in spatial ecology