Friday, August 8, 2008
Exhibit Hall CD, Midwest Airlines Center
Esteban Muldavin, University of New Mexico, Natural Heritage New Mexico, Albuquerque, NM, Steven M. Wondzell, Pacific Northwest Research Station, US Forest Service, Corvallis, OR and John A. Ludwig, CSIRO Ecosystems Science, Atherton, Australia
Background/Question/Methods The Ecological Survey of the Big Bend Area established 77 transects in the desert grasslands of Big Bend National Park in 1955 to monitor long-term vegetation change. These transects have been re-charted at the species level more or less decadally with the most recent charting by us in the fall of 2007. Now 50 years later, these permanent plot studies provide one of the longest records of grass and shrub dynamics in desert Southwest. Results/Conclusions
Our preliminary results from one soil type indicate that grass cover increased linearly coming out of the 1950’s drought until 1981 where it reached a plateau between 15% and 20% cover through 2007. Shrub and grass covers were nearly equal in the early decades, and increases tracked each other closely. But after 1981, shrubs continued to increase linearly and now account for more than twice as much cover has grass (37% in 2007). Succulents showed a similar continuous trend in cover increase (now 12%). This suggests that recovery of desertified grasslands is a mixed process with definite increases in overall cover of both grasses and shrubs coming out of the most severe drought of the 20th century. But that there may be limits on grass response, possibly reflecting more dynamic summer precipitation versus the more stable winter precipitation regime that favors shrubs.
