Geology topics

John W. Steiger

Publications and source records attributed to John W. Steiger.

3 recordsLinked to original sources

USGS2000

Recovery of perennial vegetation in military target sites in the eastern Mohave Desert, Arizona

The effect of the age of geomorphic surfaces on the recovery of desert vegetation in military target sites was studied in the Mohave and Cerbat Mountains of northwestern Arizona. The target sites were cleared of all vegetation during military exercises in 1942-1943 and have not been subsequently disturbed. The degree of recovery was measured by calculating percentage-similarity (PS) and correlation-coefficient indices on the basis of differences in cover, density, and volume of species growing in and out of each target site. PS values, ranging from 22.7 to 95.1 percent (100 percent = identical composition), indicate a wide range of recovery that is partially controlled by the edaphic properties of the geomorphic surfaces. Statistical analyses show a strong pattern that indicates a greater variability in the degree of recovery for sites on older surfaces than on younger surfaces and a weak pattern that indicates an inverse relation between the degree of recovery and geomorphic age. Comparisons of the different effects of target site construction on the edaphic characteristics of each target site provides an explanation for these patterns and suggests the soil properties critical to the recovery process. Statistically significant negative or positive response to disturbance for most species are independent of the age of the geomorphic surfaces; however, there is strong evidence for a shift in response for the common perennial species Acamptopappus sphaerocephalus, and to a lesser extent, Salazaria mexicana, Encelia farinosa, and Coldenia canescens, among different geomorphic surfaces.

Arizona↗

USGS1987

Dynamics of Mojave Desert shrub assemblages in the Panamint Mountains, California.

We studied shrub communities in the Panamint Mountains of the Mojave Desert to determine whether vegetational changes after disturbance can be characterized as succession according to modern successional theory. We found, on a variety of disturbed and undisturbed sites, that the rate of change was a function of the type and age of disturbance. Recent debris—flow deposits were colonized by shrub assemblages of different species composition than those on the surrounding, older debris—flow deposits and other geomorphically stable surfaces. Colonization of human—disturbed sites was highly variable, but species compositions were different from the predisturbance species composition. In Grayia—Lycium assemblages, Grayia spinosa reasserted its dominance over colonizers relatively quickly. In Coleogyne assemblages, typically found on older geomorphic surfaces, species composition differences persisted considerably longer, depending on the severity of the initial disturbance. Extremely stable assemblages, dominated by Coleogyne ramosissima, occurred on the oldest, least disturbed surfaces. The variability of species composition among disturbed sites was greater than the variability among undisturbed and geomorphically stable sites, in accord with convergent succession. Models of desert succession should consider several factors: (1) colonization is dependent largely on the severity of disturbances and residual biotic components; (2) the time span for recovery may be longer than past periods of climatic and geomorphic stability; and (3) colonizing species may have considerable range in their life—history strategies.

California↗

USGS1986

Recovery of compacted soils in Mojave Desert ghost towns

Residual compaction of soils was measured at seven sites in five Mojave Desert ghost towns. Soils in these Death Valley National Monument townsites were compacted by vehicles, animals, and human trampling, and the townsites had been completely abandoned and the buildings removed for 64 to 75 yr. The soils studied (generally sandy, mixed, Typic Calciorthids) were derived from granitic or volcanic alluvium at elevations from 1310 to 1730 m. Compaction measurements in the townsites, including penetration depth, penetration resistance, bulk density, and peak shear stress, indicated that only one site had completely recovered to ambient soil conditions after 75 yr. Recovery times extrapolated using a linear recovery model ranged from 80 to 140 yr and averaged 100 yr. The recovery times were related to elevation, suggesting freeze-thaw loosening as an important factor in ameliorating soil compaction in the Mojave Desert.

California↗