Vegetation change in the grasslands and grassy woodlands of east-central Cape York Peninsula, Australia

Abstract

The vegetation of 64 grassland and grassy woodland sites in east-central Cape York Peninsula, surveyed by CSIRO in 1966, was re-surveyed in 1995. While the original vegetation communities had persisted at most sites, a change in species dominance was recorded at 14% of sites. Melaleuca viridiflora (ti-tree) had invaded eight sites, and increased in abundance in at least 16 of the 35 sites in which it had occurred in 1966. This had led to four out of 13 grassland sites, and three out of four mixed evergreen sites being re-classified as ti-tree woodlands. Analysis of aerial photographs covering 415 km2 showed a 10% net loss of grasslands between 1969 and 1988. These changes are attributed to a reduction in the use of fire as a management tool since European settlement. Changes were also found in perennial grass composition consistent with grazing or over-grazing, particularly in the eucalypt/ironwood communities. A shift from Themeda triandra to Heteropogon contortus parallels earlier, grazing-related changes in southern Queensland. Evidence of a decline in Heteropogon triticeus and isolated losses of Sorghum plumosum are more suggestive of localized, unsustainable overgrazing. An increase in Sorghum plumosum in wet habitats appears to be associated with recent lack of burning. These changes suggest that further intensification of cattle grazing in the area may not be possible without significantly reducing both conservation values and pasture condition.