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Runnelling, a method of habitat modification used for mosquito management in intertidal saltmarshes in Australia, alters marsh hydrology. The objective of this research was to assess if runnelling had affected the distribution of the grey mangrove (Avicennia marina (Forsk.)) at a study site in southeast Queensland. Since runnelling is carried out in diverse marshes a second aim was to assess differences in mangrove colonisation in the two main saltmarsh species in the area. These are marine couch [Sporobolus virginicus (L.) Kunth.] and samphire [Sarcocornia quinqueflora (Bunge ex Ung.-Stern.)]. Runnels at the study site were in an area dominated by Sporobolus. The mangrove area was measured by classifying digital color infrared (CIR) data obtained from aerial photographs acquired in 1982, which was 3 years before runnelling, and in 1987, 1991 and 1999, 2-14 years after. Changes in the spatial extent of A. marina were identified using difference images produced from post-classification change detection. The results showed that runnels did not significantly influence the distribution of A. marina at the study site. At a more detailed level differences in A. marina establishment in the Sporobolus and Sarcocornia areas were determined from counts of trees on the aerial photographs. There was a greater proportion of mangroves in Sarcocornia than Sporobolus and this increased over time. This may be related to differences in density between the plant species, to grapsid crab activity or to other edaphic conditions. There may be implications for runnelling in Sarcocornia marshes. The large increase observed in A. marina in the area generally is likely to be related to factors such as catchment modification or tidal/sea-level changes. It is concluded that runnelling has not led to mangrove establishment in the Sporobolus dominated saltmarsh.

A sub-tropical intertidal wetland in Moreton Bay, Queensland, Australia (27°52'S, 153° 23'E) was physically modified in 1985 to manage a mosquito breeding problem. Monitoring before and after modification was done using field and remote sensing techniques. Images from large scale colour infrared aerial photography were analysed to evaluate impacts of the modification. Analysis was by subtracting and classifying digitized images taken before and after modification. The resulting ‘difference type images’ showed the types of change and their nature. These images indicated also the spatial extent of the changes. The site has become wetter as a result of increased tidal flushing, indicated by reduced spectral values. The area modified has changed less than the adjacent mangrove inlet which floods the area. Mangroves have increased in size and spatial extent, with increased spectral values generally. The changes are consistent with reported mangrove changes in other local areas and thus are unlikely to...

Large-scale colour infrared aerial photographs were obtained for part of a tropical coastal salt-marsh in south-east Queensland, Australia. Print reflectances were classified using a numerical divisive hierarchical procedure and related to field data. Vegetation characteristics such as species, size, dry weight and density were significantly associated with each spectral class al the general (macro) and at the detailed (micro) scales. At the macro scale there were four vegetation types: pure stands of tall Sporobolus virginicus; medium-tall Sporobolus dominant but with some Sarcocornia quinqueftora; a mixed type; and finally a type dominated by Sarcocornia. At the micro scale vegetation types were further differentiated by size and dry weight of the two dominant species.

Infra-red aerial photography was used on two occasions to map the abundance and dispersion of milkweeds (Asclepias spp.). The scale at which the aerial photographs could be interpreted showed that milkweeds occur in large contiguous areas or patches. These patches are abundant, the number in any size-class declining exponentially with increasing size. Analysis of the maps using various dispersion indices and spatial autocorrelation statistic showed that patches have a clumped dispersion. Large patches tend to be surrounded by smaller sized patches. The scales at which clumping occurred indicated a close association between milkweeds and the degree of disturbance of the ‘natural’ environment by human activities. The utility of resource mapping using aerial photography is demonstrated.

The fallout isotope 137Cs has been used to trace the redistribution of soil in a cultivated paddock, in an upland catchment on the Darling Downs. The areal concentrations (mCi km-2) have been used to construct a caesiographic map which illustrates the areas of 137Cs depletion and build-up and the major areas of soil erosion and deposition, respectively, in the paddock. These areas have been graded on the basis of apparent relative intensity of erosion or deposition. Therefore, this method allows retrospective, quantitative estimates to be made of the extent and degree of soil redistribution within the last 3 decades. In addition the 137Cs results will be used to test mathematical models of erosion/deposition processes.