Small, Terrestrial Mammal Communities within Native And Non-Native Dominated Riparian Vegetation along the San Pedro and Gila Rivers in Central Arizona
* How does non-native vegetation, salt cedar (_Tamarix_ spp.), compare to native riparian vegetation in terms of its affect on small, terrestrial mammalian species and what are the habitat requirements for those mammalian species?
Under the Salt Cedar and Russian Olive Control Demonstration Act of 2006 (HR 2720), Reclamation is tasked with accessing salt cedar's value on wildlife. However, little is known of the distribution, status and/or habitat requirements of small, terrestrial mammals related to native habitat displacement. This project's goal is to increase that information base for riparian dependent mammalian species and to provide insight into Tamarix's affect on small, terrestrial mammalian communities.
Need and Benefit
Saltcedar is a non-native plant species that was introduced into the Western United States in the early 1800s for ornamental use, bank stabilization, and windbreaks. However, once established, the species began to invade nearly every riparian and wetland system in the West. The proliferation of saltcedar has been attributed to river management that has altered the natural hydrology and land uses, such as livestock grazing, land clearing, and ground water pumping (Shafroth et al. 2005).
Saltcedar generally grows on sites with relatively high water availability, such as river bottomlands or reservoir margins in arid and semiarid regions (Everitt 1980). Abundance ranges from extensive, dense, monotypic stands to small patches within a mosaic of other vegetation. As compared to native riparian tree species, salt cedar is a prolific seed producer and mature plants can withstand prolonged periods of drought and/or inundation. Only extremely xeric or halophytic plant species can tolerate the understory environment of saltcedar because of the salts that are excreted through its leaves (Hart et al. 2005). Consequently, over the last decade there has been an increase in efforts to control the spread of saltcedar as well as reclaim native vegetation where it has been removed.
As a byproduct to the control efforts, wildlife studies have been conducted to determine saltcedar's effect on ecosystem health. The impact of saltcedar upon wildlife species is variable, site-specific, and often debated. There is a paucity of quantitative information concerning the importance of salt cedar for wildlife. Most of the data collected on impacts to wildlife species have been concentrated on avian communities while other taxa have received minimal consideration. As far as mammalian studies conducted are concerned, the conclusions have shown divergent results regarding small mammals relationship with salt cedar, either with little affect (Ellis et al. 1997) or with lower abundance in salt cedar than in other vegetation types (Engel-Wilson and Ohmart 1978).
On October 11, 2006, the Salt Cedar and Russian Olive Control Demonstration Act (Act) was signed into law. It authorizes the Department of the Interior to assess the extent of the saltcedar and Russian olive infestation and to develop and demonstrate strategic solutions for long-term management and reestablishment of native vegetation. However, in order to carry out such orders, Reclamation needs to assess salt cedar's affect on the various taxa. This study will attempt to expand upon what is already known about mammalian communities within salt cedar vegetation. This study would also provide insight into the "new" riparian norm across the Western United States with native riparian desert ecosystems being displaced with salt cedar.
In addition to meeting the requirements of the Act, this type of information could assist in Reclamation's management strategies as they relate to the presence of saltcedar within project areas. Under the current conditions, there is a tension between the desire to remove salt cedar for water conservation and the need to protect salt cedar habitat when it provides habitat for protected wildlife species. This study will provide additional data on the value of this habitat type for wildlife.
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