I gave a presentation of my research on southwestern plant patterning yesterday–this was in fact an “oral dissertation defense”, according to the Masters Project Handbook. Below is a video, and the slides. I’ll hopefully be adding more material to the research page as I get around to it, including a NetLogo implementation of an existing vegetation model and possibly a Google Earth tour of some of the sites and data. First however I have to finish writing the non-oral part of the thesis.
Slides (6mb pdf)
Narrative summary of the talk:
Self-patterning of vegetation has been identified in dryland ecosystems worldwide, such as the “tiger striped” savanna of the African Sahel and the banded shrublands of Australia. In these water-limited systems plants are organized into consistent spatial structures by the facilitation of new growth in the organic shadow of existing plants. These landscapes are theorized to be more efficient at retaining rare rainfall, but are also expected to undergo catastrophic shifts if precipitation drops below difficult-to-predict thresholds.
No such banded systems have been identified in America, but I was curious if more subtle patterning could be happening in southwestern drylands which share many of the same ecosystem characteristics and display threshold response to changes in precipitation. If a form of emergent patterning were occurring in these ecosystems, it would have implications for predicting landscape response to pending changes in climate. Focusing on piñón-juniper woodlands in Arizona and New Mexico, I mapped the shapes of patches of vegetation from aerial photographs and measured their degree of spatial pattern. Estimates of surface water movement and distribution were developed for the same sites from digital elevation models. Testing the spatial correlation of these landscape characteristics indicated strong linkages between vegetation patch shape, vegetation density, and surface water hydrology. In sites in Arizona, these relationships were consistent with theories of self-patterning, suggesting that this previously unidentified phenomenon could be occurring in in an American dryland landscape.