Eyes in the Sky II > GIT Web Course > Module 2 > Week 5 > Using GIS to Analyze and Predict Invasions > Using ArcGIS to Analyze and Predict Invasions

Week 5: Monitoring Invasive Species

Using ArcGIS to Analyze and Predict Invasions

Tamarix forest in riparian zone. Image courtesy of Steve Dewey, Utah State University, United States.
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Key Investigation Questions:






Introduction

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.

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Launch ArcGIS and Orient the Map for the Investigation

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Investigate the Tamarix Invasion in the United States

Where is the present Tamarix invasion and how far has it spread across the United States? 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?
    Tamarix has been sighted in the following states:
    • California,
    • Oregon,
    • Idaho,
    • Montana,
    • Wyoming,
    • Nebraska,
    • Kansas,
    • Oklahoma,
    • Texas,
    • New Mexico,
    • Arizona,
    • Utah,
    • Colorado.

  2. What relationship do you see between rivers and Tamarix?
  3. In general, Tamarix follows rivers.
    Note: The US Rivers layer in AEJEE does not contain all rivers in the United States. So although you see Tamarix in parts of Nevada and California, the map is not displaying the invaded river.
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Create a Spatial Query to Investigate the Extent of the Invasion

Query Southwest states to investigate the extent of the invasion.

  1. Right click on the US States layer, click on Selection, and then click on Make This The Only Selectable Layer.
    9 US State Selectable Layer
  2. Click on the Select Feature Select Feature Tool tool.
  3. Click inside the state boundary of Arizona.
  4. After clicking inside the Arizona state boundary, Arizona (AZ) should now be highlighted (outlined in blue).
    1. Right click on the US States layer, click on Selection, and then click on Make This The Only Selectable Layer.
    2. Click on the Select Feature Select Feature Tool tool.
    3. Click inside the state boundary of Arizona.
    4. After clicking inside the Arizona state boundary, Arizona (AZ) should now be highlighted (outlined in blue).
    5. 10 AZ Selected
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Use the Selection, Select By Location menu option 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 called "containment".

  1. Click on the Selection menu option at the top of the map view. A pulldown context menu will open.
    11 Selection by Location
  2. Click on Select by Location.
  3. In the Select By Location dialog box, set the "I want to:" pulldown arrow to "select features from."
  4. In "the following layer(s):" Place a checkmark in the box in front of Tamarix.
  5. Set the "that:" pull down arrow to "are within."
  6. Set "the features in this layer:" to US States.
  7. 12 Select by Location Context
  8. Click OK. The buffer dialog window will be displayed on the map.
    1. Click on the Selection menu option at the top of the map view. A pulldown context menu will open.
      11 Selection by Location
    2. Click on Select by Location.
    3. Set the "I want to:" pulldown arrow to "select features from."
    4. In "the following layer(s):" Place a checkmark in the box in front of Tamarix.
    5. Set the "that:" pull down arrow to "are within."
    6. Set "the features in this layer:" to US States.
    7. 12 Select by Location Context
    8. Click OK. The Select By Location dialog window results will be displayed on the map.
    13 Tamarisk Selected Points in Blue

Discover the results of the selection

  1. Return to the map and right click the Tamarix layer.
  2. Open the Attribute Table of Tamarix.
  3. How many results have been selected?
    Right click to open the Attribute Table of the Tamarix layer.
    14 Attribute Table
    3333 Tamarix are recorded within the state of Arizona.
    15 Attribute Table with Selection

Close the Tamarisk Attribute Table by clicking on the "X" on the top right corner of the table (hint, do not click on the "X" at the very top of your screen as that will close your project.)


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

Tamarix Records:
AZ - 3333 records
NM - 422 records
UT - 326 records

Clear the selections by clicking on the Clear Selected Features Clear Selected Feature button

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Focus on Arizona Tamarix

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

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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.

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.

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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?

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Resources


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