Challenges in Restoring and Rehabilitating Arid Lands
By Jay Davison
Alternative Crops and Forage Specialist, University Nevada Cooperative Extension Authors are Rangeland Scientist and Agricultural Research Science Technician, USDA-ARS Great Basin Rangelands Research Unit, 920 Valley Road, Reno, NV 89512 charlie.clements@ars.usda.gov
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ow elevation lands within the Nevada are now subject to an increasing level of disturbances. These disturbances include wildfires made possible by the invasion of annual grasses such as cheatgrass, red brome and medusahead. Increases in urban populations bring increased recreational impacts associated with the proliferation of off highway vehicle use. Finally, competition for scarce water supplies is resulting in large scale water purchases from the agricultural sector, with the water being transferred from irrigation of farmlands to environmental or developmental uses. Arid lands as discussed in this article are defined as those lands receiving less than eight inches of precipitation annually. As more of these lands are disturbed, problems with wind erosion and blowing dust are becoming serious issues for neighboring property owners subject to wind-blown soil deposits on their properties as well as State officials concerned with air pollution from the dust particles. Another serious problem with many of these lands is the proliferation of noxious or injurious weeds which invade the bare areas when precipitation or flooding is adequate to allow the weeds to proliferate. The weed populations facilitate more frequent rangeland fires and insure that the desirable native species are never able to colonize the disturbed areas due to competition from the weeds for nutrients, light and water. Natural or passive restoration of these lands is slow to nonexistent for a host of reasons. The primary reason is the lack of adequate precipitation which occurs during active plant growth periods. While most people know that Nevada is “dry” few realize just how little precipitation most of Nevada receives (Figure 1). The precipitation amounts shown demonstrate that a majority of the southern and western portions of Nevada only average about 5” of precipitation annually and most of the other areas average around 10”. In fact, the actual amount of precipitation that can be expected in any one area may normally be significantly less than the average (Figure 2). In the case of the Lahontan Valley, although the average annual precipitation is nearly 5”, in 25 of the past 36 years the annual precipitation 36 March 2017
amounts were less than 5”, and in many years the precipitation was significantly less than 5”. This pattern is repeated in a majority of the arid portions of Nevada. There are numerous shrub species commonly used in reclamation projects in the more arid regions of Nevada (Figure 3). All of these shrubs typically require at least 6” of annual precipitation to survive, although 8” is strongly preferred. It is very obvious when viewing precipitation data that in the past 36 years, there is very little chance of successfully seeding these rangelands. In only four of the past 36 years did the annual precipitation exceed the amount recommended by reclamation specialists for successful seeding of arid land shrub species. Grasses adapted to seeding arid lands have very similar precipitation requirements, but due to a shallower rooting system they perish more quickly under successive dry years. For that reason, most of the extremely arid lands are dominated by shrubs rather than grasses. Another important point related to natural precipitation is that the majority of the precipitation in most of Nevada occurs during the winter months when almost all plant growth has ceased. Very little precipitation occurs during the summer months and often newly seeded plants desiccate and die due to a lack of moisture during the
summer months. Therefore, supplemental irrigation is almost always necessary when undertaking a reclamation project on these arid lands. Recent research in Nevada has demonstrated that an additional 12” of irrigation water applied in the spring and early summer of the first and second year is adequate to insure that the seeded plants survive. A second major challenge to successfully reclaiming these lands is the fact that when supplemental irrigation is applied or above normal precipitation amounts occur during the seeding year, competition from weeds will normally prevent the seeded species from becoming established. Winter annual weeds such as cheatgrass, red brome, tumble mustard, flix weed etc. compete very effectively for nutrients, space and light with the seeded species. Because they occur in such great densities, emerge earlier and grow faster, the planted species have little chance of success regardless of the amount of water available. Summer annual species including kochia, Russian thistle, lambsquarter, Mexican lovegrass and others grow throughout the summertime and thrive even after the irrigation water is discontinued and soon dominate the planted area and the seeding fails.
Figure 1. Notice the severe aridity of more than have of the major cities in Nevada. The Progressive Rancher
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