Assessment and Ranking of the Agents Influencing Woody Plant Expansion in Arizona

Kelley O'Neal, University of Maryland, kelley.oneal@gmail.com (Presenter)
Tatiana Loboda, University of Maryland, loboda@umd.edu
John Rogan, Clark University, jrogan@clarku.edu

Woody encroachment and proliferation within dryland ecosystems is potentially the second largest portion of the North American carbon sink and one of the largest areas of uncertainty. This research examines a semi-arid grassland located in southeastern Arizona to better understand the amount of woody encroachment occurring and the agents driving changes in woody plant cover amounts. While it is understood that historical land use, land management, and climate variation have facilitated initial woody encroachment in the region, the current relative influence of land use, land management, fire/fire suppression, and site specific conditions on change in woody plant cover remains unclear. Ongoing research indicates that land use, land management, and fire suppression are the primary agents causing increased woody plant cover in Chihuahuan grasslands. However, there is disagreement as to the dominant agent(s) causing this land cover modification.

Woody plant cover and change over time was mapped using a Landsat time-series. Results show the change in woody plant cover varies spatially with an average two-fold increase over twenty-five years. Agents of woody plant cover were also mapped, including fire, anthropogenic, edaphic, and topographic agents. The Random Forests ensemble classifier was used to rank the influence of each variable and determine the dominant agent of woody plant cover change in the region. Initial woody cover, number of times burned, elevation, and grazing were ranked as the most important agents of woody encroachment, indicating the importance of historical land management and disturbance, frequent fire, topography and correlated precipitation, and land use. Precipitation trends were not incorporated into the Random Forests analysis due to a lack of suitable modeled data.

Presentation Type:  Poster

Session:  General Contributions   (Tue 4:35 PM)

Associated Project(s): 

• Justice, Chris: Impacts of grazing, fire, and precipitation variability on woody plant cover in Chihuahuan Desert grasslands, USA ...details

Poster Location ID: 210