Fall 2005

Sometimes a Great Notion:
Visualizing Forest Fragmentation

It may seem pretty obvious that American forests are being split apart by roads, houses, and strip malls, but, until recently, it was difficult to visualize the extent and magnitude of forest fragmentation in the United States. Until, that is, Southern Research Station (SRS) researcher Kurt Riitters and his collaborators started applying a method called “moving windows” to landscapescale analysis.

Riitters and three fellow landscape ecologists—James Wickham, Timothy Wade, and John Coulston—have come up with a deceptively simple method to make fragmentation of the landscape visually apparent. The four—Riitters and Coulston from the SRS Forest Health Monitoring unit in Research Triangle Park, NC, and Wickham and Wade from the nearby Environmental Protection Agency (EPA) National Exposure Research Laboratory—are using moving windows to produce information about forest fragmentation for highlevel clients such as the Montréal Process, the H.J. Heinz Center, and the European Commission—as well as for regional planners in the Southeast.

A Window Opens

Riitters and Wickham started looking at ways to visualize landscape patterns more effectively in the 1990s, when they both worked at the Tennessee Valley Authority Landscape Ecology Project in Norris, TN. By 1995, when they published a landscape atlas of the Chesapeake Bay watershed (with the help of Wade, then at the Desert Research Institute in Reno, NV), the two were well aware of the limitations of the approaches used to assess forest fragmentation. Analysts would start out with landcover maps generated from Landsat satellite images that were divided into millions of tiny squares called pixels (short for “picture elements”). They would count the pixels in a given area for each type of landcover and assign a number, or fragmentation value, to represent all of the pixels in the area. This aggregating method meant throwing away original information from the images, as well as removing the ability to make comparisons.

For the 1995 atlas, Riitters and Wickham introduced the idea of using moving windows to recover this lost information. “When you make a map of forest fragmentation using moving windows, it’s like focusing a camera so that the detailed patterns stand out,” says Riitters. “But the main benefit is that each pixel now has its own unique fragmentation value, a number that describes its particular context.” (...continued...)