Northern Arizona University

My research in the Sisk Lab of Landscape Ecology and Conservation Biology at NAU focuses on testing methods to grow native plants along the Virgin River at Zion National Park, Utah. Currently, the upland banks are dominated by exotic grasses, Bromus tectorum (cheatgrass) and Bromus diandrus (rip-gut brome), which do not allow native plants to thrive in the main canyon. These grasses mature earlier in the growing season than native plants, thereby consuming limited nutrients. The bromes then set seed and continue the cycle of outcompeting natives and increasing their presence in Zion Canyon. This build-up of dense, fine fuels is a potential hazard for carrying fire rapidly in the canyon, and is a concern for park management since the park attracts 2.7 million visitors annually. My work will provide recommendations to the park for treatments to remove the exotic grasses and revegetate with native plants, using local native seed.

In addition, I am studying the effects of herbivory and trampling on the recruitment of cottonwoods and willows in Zion Canyon. The cottonwoods and willows today are aging with little recruitment. Without a new cohort of trees to replace them, the ecology of the canyon will drastically change when the current trees die off. The channelization of the Virgin River by revetments installed in the 1920s and '30s has prevented the development of gradual floodplains, the sites required for cottonwoods and willows to germinate. In 2005, flooding events provided the conditions for cottonwood and willow seedlings to establish in areas where revetments have failed and floodplains have formed. I have set up paired plots along the river to determine if fencing helps seedlings to mature when herbivory and trampling are excluded.

Email: mpd23@nau.edu