were sampled where grazing had ceased in 2000 (grazed). Data on plant species were taken in Spring 2005. Further results and methods used are described in ...
Appendix 2 Vegetation and grazing Surveys of species richness of flowering and non-‐flowering plants and cover were made during 2005 in all the same habitats sampled for bees in 2001 (riparian, mesquite, grassland and scrub) except the field (Minckley 2012). For background, the results of that study are summarized here (see Table below). The 2005 study found habitats varied 2-‐fold in plant species richness with fewer species in the mesquite and riparian habitats than in the grassland and scrub habitats. The effect of grazing on the plant community was evident despite the considerable time since grazing had stopped (4 and 26 years in Mexico and in the United States, respectively). The riparian and mesquite habitats had significantly more plant species in the grazed area than they did in the ungrazed areas, in contrast to grassland and scrub habitats where plant species richness did not change (Table S1). Plant diversity was lowest in the ungrazed riparian habitat where shading from the dense cottonwood (Populus fremontii) canopy deterred establishment of subshrubs and herbaceous vegetation. Grazing resulted in higher plant species richness in riparian habitats because the diminished tree recruitment allowed for greater light penetration and enabled short-‐statured plant species to establish. Although the same number of species were in grazed and ungrazed areas of the grassland and scrub habitats, it is not clear if this indicates the areas were not grazed intensively enough to have an impact to if successional changes in these water-‐limited plant communities were slower than what could be detected in the 22 year differences of the grazed and ungrazed areas (Minckley 2012). Table S1. Average number (+ standard deviation) of plant species in plots from four habitats in the San Bernardino Valley, Arizona, USA and Sonora, Mexico. In each habitat, four plots were sampled where grazing had ceased in 1979 (ungrazed) and four plots were sampled where grazing had ceased in 2000 (grazed). Data on plant species were taken in Spring 2005. Further results and methods used are described in Minckley (2012). HABITAT GRAZING NUMBER HISTORY of SPECIES _________________________________ Mesquite Ungrazed 9.75 + 2.17 Mesquite Grazed 14.25 + 2.06 Grass Ungrazed 20.25 + 5.68 Grass Grazed 24.25 + 2.63 Riparian Ungrazed 12.25 + 2.75 Riparian Grazed 25.0 + 4.69 Scrub Ungrazed 18.63 + 5.32 Scrub Grazed 20.13 + 6.83
Minckley, R.L. (2012) Trajectory and rate of desert vegetation response following cattle removal. Gottfried, G. J., Ffolliott, P. F., Gebow, B.S., & Eskew, L.G., compilers. 2012. Merging science and management in a rapidly changing world: biodiversity and management of the Madrean Archipelago III. 2012 May 1-‐5, Tucson, AZ. Proceedings RMRS-‐P-‐67. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.