Initial Publication Date: March 13, 2010

Week 5: Monitoring Invasive Species

Using AEJEE to Analyze and Predict Invasions

Tamarix forest in riparian zone. Image courtesy of Steve Dewey, Utah State University, United States.
top of page

Key Investigation Questions:

  • How has the Tamarix plant's invasion proceeded over time?
  • What are the factors limiting Tamarix's spread through the entire United States?
  • How are scientists using Satellite imagery to aid in predicting Tamarix's next move?


Tamarix, or saltcedar, grows as a woody shrub or small tree. It was introduced to the United States in the 1850's as an ornamental plant capable of erosion control. It successfully adapted and quickly spread into wetlands displacing native trees such as cottonwood, willow and mesquite. Now, Tamarix has invaded nearly all the watercourses and wetlands in the Southwest US. As one of the most successful and common invasive species in the United States, it has overtaken nearly one million acres of habitat. Since it can transpire as much as 300 gallons of water per day, it is capable of causing a wetland to completely dry up. Additionally, Tamarix has a tendency to increase the salinity of the soils in which it grows and it is of little or no value to wildlife. Although Tamarix is difficult to eradicate, in locations where it has been eliminated native vegetation and wildlife have returned and flourished.

top of page

Launch AEJEE and Orient the Map for the Investigation


  • Launch AEJEE by double-clicking its icon on your desktop or by clicking its icon in the dock (Mac) or Launch Bar (Win).
  • Choose File > Open, navigate to ESRI/AEJEE/Data/Invasive_SpeciesAE and select the file inv_spc.axl. Then click Open.
  • Once the map opens, turn on the US Rivers and Tamarix layers. Use the Zoom In Zoom in tool to click and drag a box, around the contiguous United States.
  • Make Tamarix the active layer and zoom to its extent. The map will now be focused on the Western United States where the Tamarix invasion began.
  • Turn on the US States layer.

top of page

Investigate the Tamarix Invasion in the United States

Where is the present Tamarix invasion and how far has it spread across the United States?

  • Make Tamarix the active layer by clicking its name.
  • Click once on the Select Feature select features button tool in the toolbar.
  1. In the drop down menu, choose the Rectangle selection tool.
  2. On the map, click and drag to draw a rectangle around a group of Southwestern states.
  3. When the tool is released the selected Tamarix points are highlighted yellow. These points are selected because Tamarix is the active layer.
  • Clear the selections by clicking on the Clear All Selection Clear Selections button.
  • Change the active layer to US Rivers and repeat the selection process.
  • How do the results differ?
  • Clear the selections by clicking on the Clear All Selection button.

top of page

Where is the Tamarix invasion the most severe?

Tamarix can be found throughout the Southwest United States. Some states have more of a Tamarix problem than others, but because Tamarix spreads easily and is very difficult to eradicate, plant biologists are keeping a close eye on the situation.

Zoom and Pan around the map to get a better idea of the extent of the invasion and to answer the following questions.

  1. In which states has Tamarix been sighted?
  2. What relationship do you see between rivers and Tamarix?

top of page

Create a Spatial Query to Investigate the Extent of the Invasion

Buffer Southwest states to investigate the extent of the invasion

Make US States the Active layer and select Arizona with the Select Feature > Polygon selection tool.

select feature close up

  1. Make US States the Active layer.
  2. Click and hold on the Select Feature select features button tool. Choose the Polygon selection tool. (Pictured to the right.)
  3. Click just inside the state boundary of Arizona.
  4. Release the selection tool, Arizona (AZ) should now be highlighted. If you get several states, try again. Hint: You might need to zoom into the states to get more accurate results.

top of page

Use the Buffer buffer tool icon tool to select the records from the Tamarix database that are contained within the boundaries of the state of Arizona. This is a type of spatial query that is called "containment".

buffer box 2 Buffer dialog box.

  1. Click on the Buffer tool in the toolbar. The buffer dialogue box will open. (Pictured right)
  2. Set the Buffer Distance to 1.
  3. Set the Buffer Units to Meters.
  4. Check the box "Use the buffer to select features from this layer".
  5. In the pull down menu of layers, choose Tamarix.
  6. Click OK. The buffer dialog window will automatically close and the selected points will be displayed on the map.

Discover the results of the selection

  1. Return to the map and make Tamarix the active layer.
  2. Open the Attribute Table of Tamarix.
  3. How many results are have been selected?

Repeat this entire process with several other Southwestern States to find the next most invaded state.

Clear the selections by clicking on the Clear All Selection Clear Selections button.

top of page

Focus on Arizona Tamarix

As you just discovered, Arizona's Tamarix invasion is the severe. Now, you'll investigate the specific Arizona rivers that have been invaded by Tamarix.

  • Turn on and activate the AZ Rivers layer.
  • Use the Zoom to extent of the active layer Zoom to Full Extent tool to zoom into the state of Arizona.
  • Click on the AZ Rivers layer with the Identify tool identify button to learn the names of the rivers in Arizona which are invaded by Tamarix.
  • In the identify results box, scroll down to find the field "Name".
  • List several rivers that have been invaded by Tamarix.
  • Other Tamarix invasions do not appear to be in streams. Since Tamarix needs wet conditions to survive its first year, what types of areas might also be suitable habitat for Tamarix?

top of page

Add Satellite Data to Connect Tamarix Spread with Vegetation Index

By using the satellite data of vegetation health the scientists at NASA and USGS are able to use habitat preferences, such as moist soils and low elevations, to begin to predict where Tamarix plants were most likely to appear in the future.

Adjust the layers on the map for the investigation.

  • Turn off the US States, Countries and AZ Rivers layers.
  • Turn on the vegetation index image file NDVI_6.1.09.TIFF
    This file, named NDVI_6.1.09.TIFF, shows where the vegetation has "greened up" with spring vegetation. It is a geospatially calibrated image file, or GEO TIFF, from June 6th, 2009. It was downloaded from NASA NEO.
  • Make Tamarix the active layer.
  • One the NDVI file has loaded in AEJEE, choose Zoom to the extent of the active layer in this case, Tamarix points.
  • If necessary, adjust the layers so that the NDVI_6.1.09.TIFF, image is below the Tamarix layer.
  • Zoom and Pan to compare the location of the Tamarix points to the green regions of the image. Areas with healthy vegetation are prime locations for new invasions of Tamarix.

Plants are sensitive to their environment and so they serve as a good indicator whenever there is change. Scientists routinely produce global NDVI maps to help them monitor and investigate shifts in plant growth patterns that occur in response to climate changes, environmental changes, and changes caused by humans. Farmers and resource managers also use NDVI maps to help them monitor the health of our forests and croplands. So these maps are useful both for scientific research as well as societal benefit.

Notice that the in Arizona the Tamarix invasion prefers the lower elevations where there is more desert. It is found in the river corridors and other low lying wet areas.

top of page

Add Elevation to the Map to Solve the Puzzle

So far we have observed that Tamarix invasion patterns follow the river corridors and also other areas that appear to have healthy green vegetation in the satellite NDVI image. So, why doesn't Tamarix invade everywhere? What is the missing element in the puzzle?

  • Turn on the elevation Elevation > 2km layer. Zoom to the full extent of this layer.
  • Use the zoom and pan tools to look at the map. Are there many Tamarix sightings at elevations above 2 km? What climate conditions change at this elevation?
  • Turn on the US Rivers layer on and off as needed and /or move the US Rivers layer above the Elevation layer.
  • Based on the data in the Satellite NDVI image, Elevation > 2km, and the US Rivers layers, predict the direction that you think will Tamarix move in the next few years in the United States.
  • Use the Identify identify button tool, your selection skills and the layers in the project to answer the following questions;
    1. Which US Rivers seem to be the most likely to be invaded?
    2. Where would you send your land management team next?
    3. What factors could be limiting the spread of Tamarix?
  • Quit AEJEE. Do not save your work.

top of page


top of page