PARENT SESSION
Oral Session #16: Disturbance in diverse systems: Flooding and other. Presiding: T. Stohlgren.
Monday, August 6, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
A century of increase in species richness at a Sonoran Desert site protected from prolonged human impact .
Guo, Qinfeng1, Bowers, Janice2, Turner, Ray2, Betancourt, Julio2, 1 2
ABSTRACT- The nature and duration of human impacts are seldom considered in site selection for long-term ecological research or biodiversity studies. Among the longest monitored sites in the world is Tumamoc Hill, a volcanic outcrop overlooking a formerly perennial reach of the Santa Cruz River. Tumamoc Hill and the adjoining valley have sustained more than a thousand years of prolonged human impact, culminating in the founding of the modern city of Tucson. Since protection from grazing and other impacts in 1907, overall species richness and environmental heterogeneity has continued to increase on 10 permanent vegetation plots. Both alpha and gamma diversity rose dramatically over time while beta diversity was virtually unchanged, indicating a long time lag in the response of species composition to environmental changes. Species richness increased at different rates across all plots. Plant density and cover, however, diverged more significantly than species composition across all the plots. Rates of change were higher on species-rich than on species-poor plots. Increase in habitat heterogeneity was more dramatic when measured by plant cover, followed by plant density and species composition (the rates of changes: cover > density > species composition). Our long-term observations suggests that it takes at least a century for perennial vegetation to fully recover from prolonged prehistoric and historic impacts in Sonoran Desert and similar desert communities.
KEY WORDS: diversity, human impact, recovery, Sonoran Desert