occur (Wells 1961, Vasek et at. 1975a,b). These invader species are usually perennial forbs or subshrubs which were only secondary constituents of the previous undisturbed communities. If invader species do occur, then regeneration of long-lived dominant perennials may be expected to return after clearing in a sigmoid fashion, i.e., slow initial regeneration followed by rapid intermediate development as the invader species begin to be outcompeted (Vasek et at. 1975b). This can be a time consuming process, as evidenced by clearing effects still being noticeable in a heavily disturbed desert area 33 years after the disturbance took place. If seeding of perennial grasses is attempted in order to take economic advantage of the moderate microclimate under collector arrays, and in an attempt to discourage weed growth, then several considerations may be important. Desert grassland species are often soil texture specific (Herbel et at. 1973), and seeding is often not successful on highly erosive sites or ones which form a hard surface crust (i.e., desert pavement). Establishment of rangeland grasses is also generally unsuccessful on sandy soils of arid regions due to windblast destruction of seedlings (Fryvear et aZ-,^1973), although the shelter effect imposed by the solar collectors may give mechanical protection to seedlings from sand blast (Rosenberg 1974). In general, the desert literature indicates that succession is a variable and often unpredictable phenomenon. This variability also tends to increase with disturbance, thus complete destruction of above-ground communities would be the hardest to predict with regard to revegetation. A further generality is that rate of revegetation from complete clearing is inversely related with the degree of aridity in a disturbed area, meaning that areas of higher relative production and diversity will revegetate more quickly. Thus, although significant areas may be cleared in the construction phase of these solar projects, the more mesic environment provided by shading and wind deflection should aid revegetation of the sites relative to disturbance in the open desert. Succession of plant communities will have a profound impact on animal
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