Vegetation Changes since 1902

Vegetation Changes since 1902 on the Santa Rita Experimental Range (adapted from McClaran 2003)

Fig. 2-3-4_Photo sequence showing relative changes in density of mesquite between 1903, 1948, and 1988.gif

Medina 1996 Changes in density of mesquite between 1903, 1948, and 1988

We know more about vegetation change on the Santa Rita Experimental Range since 1902 than is known about any other 50,000-acre area in the world. This record is only possible because important techniques of measuring vegetation changes were developed on the Santa Rita, such as repeat photography and the line intercept transect method, and because they were applied often and broadly. The long record of experiments and systematic observations nourishes the interpretation of these changes. Together, they describe a steady increase of mesquite trees, four cycles of burroweed eruption and decline, one cholla cactus cycle, interannual and interdecadal variation in native grass composition, and the recent dominance of the nonnative Lehmann lovegrass. The most conspicuous change is the increase of mesquite, which began before 1902 when the spread of seed by livestock and cessation of fire led to the establishment of mesquite in the open grasslands. The growth of these plants and subsequent recruits transformed the grasslands into a mesquite-grass savanna, and neither the elimination of livestock grazing nor the occasional fire has reversed this change. Burroweed cycles appear to be more closely related to winter precipitation patterns and maximum plant longevity than land management activities. Similarly, the increase of Lehmann lovegrass is largely independent of livestock grazing management.

More details on the vegetation changes on the SRER can be found in Publications (e.g. Proceedings from the Centennial Conference 2003) while the vegetation data collected from 1953-present are available for download at Long-term vegetation transects.


McClaran, Mitchel P. 2003. A Century of Vegetation Change on the Santa Rita Experimental Range. In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. pp. 16-33.
Medina, Alvin L. 1996. The Santa Rita Experimental Range: History and Annotated Bibliography (1903-1988). General Technical Report RM-GTR-276 Rocky Mountain Forest and Range Experiment Station Forest Service U.S. Department of Agriculture. 67 p.