Aerial photography for assessing vegetation change: a review of applications and the relevance of findings for Australian vegetation history [Review]

摘要

Studies attempting to calibrate vegetation attributes from aerial photography with field data are reviewed in detail. It is concluded that aerial photography has considerable advantages over satellite-based data because of its capacity to assess the vertical dimension of vegetation and the longer time period the record spans. Limitations of using the aerial photo record as digital data include standardising image contrast and rectification. Some of these problems can be circumvented by manual techniques, but problems of crown exaggeration that varies with photo scale and variation in contrast between the textures of tree crowns and the ground remain. Applications of aerial photography for assessing vegetation change are also reviewed and include deforestation, reforestation, changes in vegetation boundaries, tree density, community composition and crown dieback. These changes have been assessed at scales ranging from individual tree crowns to regional landscapes. In Australia, aerial photography has provided a clear demonstration of deforestation rates and the expansion and contraction of forest and woodland, which is generally attributed to changes in grazing and fire regimes. It is suggested that manual techniques with point-based sampling, digital processing of data for complete spatial coverages and the application of photogrammetric measurements with stereo-plotters are all techniques with great promise for utilising this underrated medium for assessment of vegetation dynamics.