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Effect of pasture type on regeneration of eucalypts in the woodland zone of south-eastern Australia
(2003)
Although eucalypt regeneration is an uncommon event in the highly modified rural environments of southeastern Australia, it still occurs on some roadsides and even in grazed paddocks. A number of observations suggest that under grazing, regeneration is more likely to occur in native pastures than in those dominated by exotics. The apparently adverse effect of exotic pastures was investigated by monitoring growth and survival of eucalypt seedlings — either planted or from sown seed — on the Central Western Slopes of NSW. Survival of seedlings arising from direct drilled seed of Eucalyptus albens and/or Eucalyptus melliodora in exotic pastures was generally low. However, survival was higher for seedlings emerging in spring (but not at other times) in an annual exotic pasture than for those emerging in spring in a perennial exotic (Phalaris) pasture. Experimental plantings of Eucalyptus melliodora seedlings adjacent to annual exotics v. a perennial native grass plant showed no significant difference in seedling growth between the two microsites though there was a trend towards enhanced survival near the perennial grass.
Within the context of other work on the regeneration of woodland eucalypts, these results suggest that: (1) competition from annual exotics is a major limitation to the survival of eucalypt seedlings in their first year; (2) competition from a perennial exotic establishing at the same time as the eucalypt seedlings is particularly severe during the eucalypt's second year. In the absence of a major disturbance such as scalping of topsoil, regeneration of eucalypts in exotic pastures is unlikely.
The assumption that ‘soils’ and ‘vegetation’ are closely associated was tested by describing soils and vegetation along a Travelling Stock Reserve west of Grenfell, New South Wales (lat 33° 55’S, long 147° 45’E). The transect was selected on the basis of (a) minimising the effects of non-soil factors (human interference, climate and relief) on vegetation and (b) the presence of various soil and vegetation types as indicated by previous mapping. ‘Soils’ were considered at three levels: soil landscapes (a broad mapping unit widely used in central western NSW), soil types (according to a range of classifications) and soil properties (depth, pH, etc.). ‘Vegetation’ was considered in three ways: vegetation type (in various classifications), density/floristic indices (density of woody species, abundance of native species, etc.) and presence/absence of individual species. Sites along the transect were grouped according to soil landscapes or soil types and compared to vegetation types or indices recorded at the sites. Various measures indicated low associations between vegetation types and soil landscapes or soil types. Except for infrequent occurrences of a soil type or landscape, any one soil type or landscape was commonly associated with a number of vegetation types and any one vegetation type was associated with a number of soil landscapes or soil types. However, significant associations between some vegetation indices, mainly density or numbers of woody species, and some soil landscapes and soil types were evident. Although many species were relatively ubiquitous, some groups of species that were restricted to one or two soil types were identified. Canonical Correspondence Analysis provided some suggestions as to which properties (e.g. texture) of these soils were associated with the presence of particular species.