Tamarisk, also known as Salt Cedar, is a non-native shrub that has invaded stream banks and waterways throughout the southwestern United States. Consuming about twice the amount of water as native plants, large Tamarisk shrubs dry-up water sources by lowering water tables. Current shrubs along parts of the Arkansas River consume enough water to supply 20 million people, or the irrigation of over 1 million acres of land.

Tamarisk also presents a significant fire hazard since it monopolizes water resources and deposits thick layers of dry brush and leaves that create a strong fuel source. In addition, the dense Tamarisk branches impede wildlife access to water sources. Not commonly eaten by native wildlife, the plant also alters soil salinity and lowers water quality for water creatures.

"One of the greatest limiting factors in understanding and controlling Tamarisk is the lack of detailed, high-resolution maps of the plant's distribution and abundance," said Shannon McCormick, Kearny County Commissioner. "We needed a quick, cost-effective and repeatable method of surveying the area."

Kearny County turned to Colorado Springs, Colo.-based NCDC, a DigitalGlobe business partner that specializes in the use of high-resolution satellite imagery for invasive plant delineation, wildfire risk assessment, forest composition analysis and emergency planning. Using QuickBird satellite imagery and Feature Analyst Software from Visual Learning Systems (Missoula, Mont.), in addition to proprietary algorithms, NCDC created a detailed inventory used for developing treatment and control plans. NCDC also created visual, image-based maps to assist in communicating with government agencies and private landowners.

QuickBird imagery collected in Sept. 2004 was used by NCDC to assess 32 miles of the Arkansas River. The 874 acres of mature Tamarisk in that area consume about 682 million gallons of water per year, equaling a loss of about $495,000 worth of corn. An estimated $655,000 would be needed to control and restore the Tamarisk growth areas.

According to Jason San Souci, director of Remote Sensing Applications at NCDC, "The growth and spread of Tamarisk could not only be controlled, but prevented, if the extent of the infestations were precisely known. For this reason, Kearny County's management strategy must include regular mapping and monitoring with high-resolution satellite imagery."

NCDC has developed a set of algorithms to classify and enhance the 60-centimeter resolution QuickBird imagery, which shows details on the ground as small as two feet across. NCDC also provided Kearny County with Earth Map Solutions' AgroWatch Canopy Density Map, ESRI Shapefiles of salt cedar infestations and cottonwood trees, and a QuickBird imagery-based 3-D virtual "fly-through" of the Arkansas River project area.

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