Long-term influences of shrub removal and lagomorph exclusion on Chihuahuan Desert vegetation dynamics

Cover of perennial species in long-term experimental plots in a creosotebus h (Larrea tridentata Sess. & Moc. Ex DC.) dominated community in the Chihua huan Desert was monitored for 56 years. Sixteen 21.3 x 21.3 m plots were es tablished in 1938-39 to evaluate the effects of lagomorph exclusion and shr ub removal. Major dominant shrubs were individually severed at ground level and removed by hand in 1939, and this process was repeated after measuring plant cover in 1947, 1956, 1960, 1967, 1989, and 1995. Lagomorphs were exc luded with poultry wire fencing. Shrub removal increased (p less than or eq ual to 0.05) the basal cover of two major desert grass species, black grama (Boulteloua eriopoda Torr.) and spike dropseed (Sporobolus contractus A.S. Hitch.) between 1939 and 1995, but differences were not evident until 50 y ears after initial treatment. Temporal effects of lagomorph exclusion were less pronounced than shrub removal. Clearly, shrub dominance has an extreme ly important and lasting role in determining vegetation community structure in this arid environment, even when above-ground shrub structures are peri odically removed. (C) 1999 Academic Press.