Taming the Tamarisk

On one side, high above the earth, is the QuickBird satellite, a commercial spacecraft able to offer submeter resolution imagery of Earth's surface.

On the other side is a pretty, hardwood shrub -- the tamarisk, also known as the salt cedar.

Growing from 5 to 20 feet tall, the tamarisk was originally introduced into the United States from Eurasia in the early 1800s as an ornamental plant. Because of its dense, deep root system, settlers in Southwestern states planted salt cedar along streambeds to prevent erosion from flooding. Over the years, tamarisk spread from the Colorado River basin to New Mexico, and as far east as Texas.

This proved disastrous for ecosystems in affected states, including Kansas. Kearny County, Kan., is fighting the spread of tamarisk along the Arkansas River with a combination of satellite imagery and GIS.

Targeting the Tamarisk

"We needed to find out the population of salt cedar on our stretch of the river and see if we could more accurately determine the full use of water by the salt cedar," explained Shannon McCormick, a Kearny County commissioner. "People don't really understand it is more than just a weed problem. But if you relate the use of the water by salt cedar to the acreage of corn you could water with that, then you can accurately estimate the economic impact. Everybody understands dollars."

Rough estimates reveal that tamarisk along parts of the Arkansas River in Kansas consume enough water to supply 20 million people or irrigation of more than 1 million acres of land.

Past efforts to estimate the extent of salt cedar infestation involved either extensively flying over infested areas or hiring people to scout plant growth on foot -- a long and laborious task.

"Flying, you just get too much air and you still only end up with a guesstimate on how many acres," McCormick said. "With digital imagery, on the other hand, and using the spectrum of the plants, you can get a very accurate number. You don't just end up with some abstract type of graph. You get actual maps that are really animated and friendly to use. We were happy with the results."

The tamarisk is now labeled an invasive species because it displaces native plants through its aggressive growth.

"In short, salt cedar is just a nasty plant," said Jason San Souci, director of remote sensing applications at the Native Communities Development Corp. (NCDC), which specializes in using high-resolution imagery for a wide range of natural resource applications, such as wildfire risk assessment, forest composition analysis and invasive species tracking. "It steals water. It's bad for fire. It's bad for wildlife. It's bad for soil. Based on the latest projections, there are probably 1.5 million acres affected in the western United States."

The tamarisk consumes far more water than other indigenous plants -- a single tree can use as much as 200 gallons per day. As a result, tamarisk infestations lower water tables and destroy wildlife habitat by sucking millions of gallons of water from streams, rivers and lakes. The plant also exudes salt from its leaves, increasing the salinity of soil, which further inhibits native plant life. And its high-density growth is a serious factor in helping spread forest fires.

"As each plant gives off 600,000 microscopic seeds every season, there is no way we are going to get rid of this problem," added San Souci. "But we can certainly control it, and we can start to restore some of the areas that have been affected. That's where we come in."

Managing the tamarisk consists of four components, he explained, control, revegetation, monitoring