Thirty Years of Change in Desert Vegetation

Shreve, Forrest; Hinckley, Arthur

On the grounds of the Desert Laboratory, at Tucson, Arizona, the perennial plants of 7 areas have been mapped and their changes followed for 30 years or less. Five areas 10 m▓ were first mapped in 1906. One area of 557 sq. miles was enumerated in 1910, and one area of 800 sp. miles was mapped in 1928. The laboratory grounds have been protected from grazing and other disturbance since 1907. All of the areas established in 1906 have shown increases in plant population, which range from 42 percent to 851 percent. The increase in the last 8 years was greater than in the preceding 22 years, due to the slow and cumulative effect of the restoration of favorable conditions for establishment. The total number of large perennials has remained almost unchanged. Of the original large perennials 30 percent died and were succeeded by nearly the same number of new individuals. The increases of total plant population are due to newly established shrubs and bushes, particularly Franseria deltoidea, Encelia farinosa, Caliandra eriophylla, Janusia gracilis and Coldenia canescens. Grasses were a negligible component of the vegetation in 1906 but now cover 2.7 percent of the 500 square miles comprised in the oldest areas. The area of 800 square miles first mapped in 1928 has increased in plant population from 163 to 466, but 197 of the 303 new plants are young individuals of the range weed Aplopappus hartwegi. The data secured in the enumerations give some indication of the length of life of the plants involved. The diversity which characterized the vegetation of the areas at the onset has been perpetuated in the nature of the changes they have undergone and in the present composition of the vegetation of the several areas. On the five oldest areas the number of species represented has decreased slightly on two and increased from 29 to 44 on the other three. There is no common thread discoverable in the history of the various areas other than

Thirty Years of Change in Desert Vegetation

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