Long-term dynamics of a degraded arid shrubland: Delayed responses and the importance of spatial processes

TitleLong-term dynamics of a degraded arid shrubland: Delayed responses and the importance of spatial processes
Publication TypeConference Proceedings
Year of Publication2003
AuthorsHavstad K, Peters DC, Murray L.W
Conference NameProceedings of the VIIth International Rangeland Congress
Date PublishedJuly 26-August 1
Conference LocationDurban, South Africa
ARIS Log Number140437
AbstractMany studies in rangelands are conducted over time periods that are too short to capture the inherent spatial and temporal variability of these systems. Extreme or pulse events that result in infrequent responses are one example that requires long-term data, but delayed responses are another that are less well-studied. Our objective was to examine the response of Chihuahuan Desert rangelands following the removal of shrubs and lagomorphs over a period of >60 years in order to capture both extreme events and delayed responses to those events. Three blocks of 16 21.3 x 21.3 m plots were established in 1938-39 to evaluate vegetation dynamics in response to shrub removal and lagomorph exclusion. Basal cover of perennial grass species did respond to treatments, especially shrub removal treatments. However, there were two important observations relative to these quantified responses. First, differences were not evident for at least 50 years. Spatially explicit processes, such as seed dispersal into these experimental plots from adjoining areas, were likely the important constraint on reestablishment of perennial grasses. Second, the temporal variability in basal cover of grasses and canopy cover of shrubs in control plots illustrate the inherent dynamics of this arid shrubland. An extreme extended drought period occurred from 12 to 17 years after the experiment was established. This climatic variability masked treatment responses until nearly 50 years after they were first implemented. In this system, we do not appreciate possible effects of vegetation management practices until they are examined during and following episodic, extreme, and acute disturbances that characterize this environment.