Leichhardt’s maps: 100 years of change in vegetation structure in inland Queensland
To address the hypothesis that there has been a substantial increase in woody vegetation cover (‘vegetation thickening’) during the 100 years after the burning practices of aboriginal hunter-gatherers were abruptly replaced by the management activities associated with pastoralism in north-east Australia. Location
Three hundred and eighty-three sites on 3000 km transect, inland Queensland, Australia. Methods
Vegetation structure descriptions from the route notes of the first European exploration of the location by Ludwig Leichhardt in 1844–45 were georeferenced and compiled. Leichhardt’s application of structural descriptors (e.g. ‘scrub’, ‘open forest’, ‘plain’) was interpreted as domains within a matrix of tall stratum and low stratum woody cover. Woody cover was also interpreted for the same locations using aerial photography that largely pre-dates extensive land clearing (1940s–1970s) and compared with their structural domain in 1844–45. The fire-sensitive tree, cypress-pine (Callitris glaucophylla) was singled out for case study because it has been widely proposed that the density of this tree has substantially increased under European pastoral management. Results
The coarse resolution of this analysis indicates that the structure of the vegetation has been stable over the first 100 years of pastoralism. For example treeless or sparsely treed plains described by Leichhardt (1844–45) had the same character on the aerial photography (1945–78). Leichhardt typically described vegetation that includes cypress-pine as having a ‘thicket’ structure suggesting dense regenerating stands of small trees, consistent with the signature typical on the aerial photography. Main conclusions
A large data set of geographically located descriptions of vegetation structure from the first European traverse of inland Australia compared with vegetation structure determined from aerial photography does not support the hypothesis that vegetation thickening has been extensive and substantial. On the contrary the study suggests that the structure of the vegetation has been relatively stable for the first 100 years of European settlement and pastoralism except for those areas that have been affected by broad-scale clearing.