Calculating Suggested Tamarisk Treatment Prescriptions

Image of Tamarisk from the 10 –Year Strategic Plan on the Comprehensive Removal of Tamarisk and the Coordinated Restoration of Colorado’s Native Riparian Ecosystems by  the Colorado Department of Natural Resources, January 8 2004

Background Information

Tamarisk or saltcedar (Tamarix spp.) is an invasive shrub or small tree introduced to the United States for erosion control and landscaping (Carleton, 1914). It has long been known as a hardy, drought tolerant species, which is easy to propagate. For these reasons it was recommended for use in windbreaks and for erosion control throughout the arid western United States. So effective is tamarisk for these purposes that even today the USDA Forest Service Agriculture Handbook 727 - The Woody Plant Seed Manual (USDA, 2010) provides information on propagation and cultivation of tamarisk. Tamarisk escaped cultivation and has spread throughout riparian areas in the southwest US (Robinson, 1965). By the 1960’s it became evident that tamarisk was spreading widely (Christensen, 1962) (Harris, 1966).

Tamarisk is an opportunistic invader, and is able to take advantage of the extensive hydrological changes introduced by dams and irrigation projects (Everitt, 1998). In addition to hydrological changes, overgrazing and other human-caused disturbances create conditions that favor tamarisk over native riparian species (DiTomaso, 1998). Tamarisk seeds germinate throughout the growing season (Brock, 1994). Once established, Tamarisk is extremely resilient to drought due to its deep root system (Halvorson & Guertin, 2003). Tamarisk can often out-compete native vegetation in riparian areas, and can extend further from a water source than native phreatophyte species such as Salix and Populus (DiTomaso, 1998).

Tamarisk infestations reduce habitat for most species, lower the water table, and increase flooding risk (DiTomaso, 1998); there may also be significantly reduced in-stream water flow. In many cases tamarisk forms monotypic stands, which generally have lower biodiversity and lower habitat value than native vegetation (Lindauer, 1983) (Brock, 1994). In addition, dense stands of tamarisk block human and animal access to riverways (Colorado Department of Natural Resources, 2004).

Removing tamarisk is expensive and time consuming  (Tamarisk Coalition, 2009).  Large dense infestations can cost hundreds of thousands of dollars to effectively treat (McDaniel, 1998) including both the initial removal of tamarisk and restoration efforts. Because tamarisk re-sprouts strongly after disturbance (Horton, 1977), mechanical removal generally needs to be followed with chemical spraying. There are several options available to the land manager for treatment methods, each with accompanying costs and limitations.

Problem Statement: A Model of Tamarisk Treatment Costs is Needed

Treatment costs for tamarisk infestations are difficult to estimate, because a detailed analysis needs to be made of the terrain and accessibility of each treatment location. A land manager may have multiple infestation sites, and multiple combinations of terrain and accessibility. This variability complicates estimation of treatment costs when assessing large areas.

We have created a spatial model which generates a cost estimate for tamarisk control work for a specified geographic area.  The model selects appropriate tamarisk treatments based on accessibility, treatment type cost, and tamarisk infestation attributes such as density and size. The model calculates costs for the selected treatments to estimate the total project cost. The estimate can inform the planning process, helping land managers understand the financial scope of a proposed tamarisk treatment project.

A PowerPoint presentation of this project can be seen here.