Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

The MODIS MCD45A1 products came in Hierarchical data (.hdf) file formats and Sinusoidal
projection, this file format is not suitable to work on ArcGIS and Erdas Imagine softwares. The
Projection is also not compatible for our database projection. Hence the .hdf file was converted
to geotiff (.tiff) file formats and the projection was reprojected to World Geological Survey 1984
(WGS 84) datum and UTM Zone 37N projection status using the MODIS reprojection tool. Then
the subset for the area of the park was extracted from the MODIS image as we did for the SPOT
image.
Data analysis
Monthly data collected from MODIS were merged to create each fire season so that they could be
analysed independently. A fire season was defined as October-December in year t, plus January-May
in year t+1. In this study therefore we had a total of nine fire seasons - 1999/2000 (incorporating
Jan-May 2000 only), 2000/2001, 2001/2002 etc. up to 2007/2008. In order to validate MODIS
images, images from 2008 were used along with the 2 m resolution SPOT image and field data
collected in 2008. A total of 3097 GPS points of burnt areas in the park were taken between March
and April 2008. The GPS points were taken following the perimeter of a burnt area. A polygon of the
burnt areas from these GPS points was then generated using xTools Pro (vector data management
extension to ArcGIS). Using these polygons as signatures the Spot image was then classified into
burnt and non burnt areas. Corresponding MODIS images were then overlaid on the classified 2008
image and visually assessed to ensure they overlapped as well as using the MODIS quality assurance
data to ensure reliability of fire detection.
Fire frequency and extent
The total number and extent of fires were calculated by counting the number of fire polygons in
each of the MODIS fire seasons and determining the total area of each polygon, respectively. Each
fire season was then overlaid on different maps classifying vegetation and soil type, altitudinal belt
and distance buffers to roads and settlements and frequency and extent were calculated as described
above. For vegetation, a number of different vegetation types could occur in one polygon, if this was
the case one fire would be considered occurring in each of the vegetation types, consequently each
of the polygons therefore would also have a specific area burnt for each of those vegetation types
occurring in that polygon. Unlike vegetation, since the boundaries of other classes were generally
easier to define, the dominant soil, altitudinal belt and buffer were used.
When the data were normally distributed a repeated measures ANOVA was used to determine
differences between each of the classes in either frequency or extent. If data were not normally
distributed a Freidman’s repeated measure analysis was carried out.
A Bonferoni’s confidence interval procedure (Neu et al. 1974) was used to see if the frequency
of fires occurring were in proportion to the area available. This gives an indication if vegetation
or soil types etc. were burnt more, less or as expected given their respective areas available. We
then assumed that those that were burnt more than expected were brunt preferentially over other
vegetation/soil/altitudinal types and those burnt less than expected were generally avoided.
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 148