Eucalypt health and agricultural land management within bushland remnants in the Midlands of Tasmania, Australia

In temperate Australia, sustainability of biodiversity in poorly-reserved woodland remnants within agricultural landscapes is a priority. Cornerstone species, such as those comprising the tree overstorey, are essential as a seed source for regeneration and for microclimate amelioration, soil erosion prevention and habitat provision in woodland ecosystems. However, trees within many woodland remnants are rapidly deteriorating in health. This has been attributed to several causes, including three decades of below average rainfall in temperate Australia. However, instances where trees are healthy and declining on either side of a management boundary indicate a key role of management in the condition of woodland remnants. We investigated the effects of past management on soil properties and vegetation understorey, and linked these with overstorey tree health across 49 sites within the agricultural Midlands of Tasmania, Australia. Sixty percent of the variation in overstorey tree health was associated with the cover of native shrubs, litter, moss and lichen in healthy sites and with cover of exotic pasture species in declining sites. Soil attributes explained 72% of the variation in tree health, with healthy sites having lower soil total nitrogen and pH, and higher soil organic carbon. A combination of soil and understorey vegetation attributes entirely separated healthy, declining and poor sites in a canonical analysis. Regression tree analysis indicated that grazing history (fencing, grazing frequency and intensity) was the primary management history factor in separating healthy and poor sites, whilst patch size, fire frequency and wood gathering were secondary, but significant, factors. Sites that were only lightly, if at all, grazed, had a fire frequency >10 years, and did not have coarse woody debris removed were healthy, indicating that the drying and warming climate of the past three decades is within the bioclimatic envelope of the species examined.(C) 2007 Elsevier Ltd. All rights reserved.