Date of Award:
Doctor of Philosophy (PhD)
Department name when degree awarded
N. E. West
A study of the microclimate of erosion control treatments was carried out in two habitat types in a semiarid southeastern Utah, salt desert shrub area. The soils are highly eroded Mancos shale and support a low density of salt desert shrub species which offers little protection against high intensity summer convectional rainstorms.
Gully plugs and contour furrows had been installed by the Bureaus of Reclamation and Land Management to prevent runoff of soil laden water which results from these summer rainfalls. Formerly this sediment was carried to the Colorado River and deposited in Lake Powell.
The purpose to t he study was to measure some parameters that influenced establishment and survival of seedlings which would stabilize the structures and increase the productivity of the area.
Mature, indigenous species close to the structures had greater vigor and provided a larger, more constant seed source. This seed source was important since original seedlings of introduced grasses have failed to establish and stabilize the structures .
Following favorable late winter and early spring precipitation, high numbers of seedlings emerged, but few survived into mid-summer. Those that did survive were found only at or near the high water line of the gully plugs and in the bottom of contour furrows.
To aid in the explanation of the differential seedling survival, soil surface moisture following rainstorms, physical and chemical soil characteristics, net radiation, soil surface temperature, and evaporation were investigated. Sampling of the 15 centimeter soil surface in the environs of the structures showed that two days after either heavy or light rainfalls, essentially no available water remained on the sloping throw positions of the structures. The bottom of the gully plugs remained flooded for several days. As a result, the seedlings were drowned. Only at the high water line of the gully plugs and in the bottom of furrows was there enough water to support seedling growth in summer.
Runoff water from summer storms carried fine material into the structures, which covered and destroyed seedlings, plus lowered infiltration and permitted much of the water to be lost through evaporation. The runoff water also carried salts brought to the surface by the desert shrubs or by the upward movement of water during evaporation from the soil surface. Sampling of soil in the environs of the structures showed no substantial build up of salt, indicating that leaching had occurred, or still was occurring. This does not mean that a build up will not result in the future. Seasonal salt distribution showed that lowest salinity levels did not always coincide with springtime when seedlings generally emerged.
Established seedlings were also exposed to a harsh environment of high soil surface temperatures (over 60 C) and high soil water evaporation rates that were detrimental to their survival.
In summary, the study showed that the erosion control structures have created a microenvironment much different from the undisturbed soil, which only permits the establishment of species with much different tolerances from the indigenous species.
Wein, Ross W., "Microenvironmental Effects of Erosion Control Treatments on Seedling Survival in a Southeastern Utah Salt Desert Area" (1969). All Graduate Theses and Dissertations. 2900.
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