An initial assessment of changes to Melaleuca distribution on a selected area of the Magela floodplain in northern Australia, Paper presented at 11th ARSPA (Australasian Remote Sensing and Photo grammetric Association) Conference, Brisbane, 3


Internal Report 411
Riley J, Lowry J & Finlayson CM
Supervising Scientist Division
Department of the Environment, Water, Heritage and the Arts

About the report

Recently, concern has been raised that woody vegetation communities – specifically, those represented by the genus Melaleuca – could displace herbaceous vegetation communities on the tropical wetlands of northern Australia. In response to these concerns we assessed changes in the distribution of Melaleuca species on a portion of the Magela floodplain in Kakadu National Park. The Magela was chosen as a study site as some 15 years ago aerial photographs had been used to determine spatial and temporal changes in the distribution of Melaleuca species. While other remote sensing products are able to detect vegetation change, it was decided that the temporal range and high spatial resolution of existing aerial photography represented a cost-effective means of providing an updated initial assessment of Melaleuca distribution on the Magela. The objectives of this study were:

  1. to establish the change in Melaleuca distribution and density on a section of the Magela floodplain (367 km2) within Kakadu National Park, by using remote sensing and geographic information systems (GIS) software to analyse changes evident from aerial photographs taken in 1975 and 1996; and
  2. to compare the results with changes described in earlier studies.

Earlier comparative studies on Melaleuca distribution undertaken on the Magela floodplain using aerial photography from 1950 and 1975 found that while there had been no increase in the area occupied by these species, forested areas had suffered a significant decrease in tree density.

The results reported here indicate that overall, there has been a 21% decrease in the tree density between 1975 and 1996. However, the extent and distribution of this decrease was variable across the study area. Conversely, there has been an increase in the distribution of Melaleuca across the floodplain in the intervening period.

Whilst the results have demonstrated that changes have occurred in one section of the Magela it is not possible to extrapolate these results to other parts of the floodplain, as further analysis would be required. However, we have shown that it is possible to do a rapid initial assessment of changes in Melaleuca distribution in a floodplain environment using remote sensing and GIS products in a time- and cost-effective manner.

For more detailed information see IR394 (Riley J & Lowry J 2002. An initial assessment of changes to Melaleuca distribution on a selected area of the Magela floodplain using aerial photography. Internal Report 394, Supervising Scientist, Darwin. Unpublished paper).