On modelling corridors between areas of remnant vegetation

In Australia so-called remnant vegetation is considered important for the survival of native birdlife. In order for the birds to be able to utilise the different areas of remnant vegetation it is important that corridors (consisting of native vegetation) exist between these areas. The corridors are very often found along roads and fences although they may be found in other places. The problem considered is whether or not it is possible to assess some sort of measure of “quality” of a corridor from Landsat satellite imagery. Using a Landsat TM image from January 1994 covering the Kellerberrin district in the central wheatbelt ca. 200 km east of Perth towards Southern Cross, Western Australia it is shown that it is possible to calibrate a ground-truth measure of corridor quality to a feature derived from the Landsat image. A number of relevant corridors which had previously been ground truth assessed for their quality (measured in “Width” and “Vegetation Score”) were digitised so that they could be used as calibration sites. The objective was to find a single feature or a combination of features from the Landsat imagery which correlates well with one or both quality indices. Generally the registered width of the corridors correspond to the width of one or two Landsat pixels. Therefore it is almost certain that a pixel covering a corridor will also contain reflectance information on adjacent land and also on the road contained within the corridor. We found that rather simple measures like local percentiles of band 5 from the image generally correlated well with the “Width” giving a correlation coefficient of -0.81. “Vegetation Score” generally did not correlate so well (correlation coefficient of-0.36). Using regression analyses techniques it was possible to generate promising corridor maps in previously unregistered areas from the Landsat TM imagery.