The results of the present study highlight that restoration of temperate sclerophyll vegetation on improved pastures requires overcoming the multiple factors that restrict native species establishment. The absence of natural recruitment, even with the aid of gaps created in the grass sward by disturbances, indicated that a reduced native seed supply in combination with the superior competitive abilities of exotic grasses were limiting factors. Furthermore, variation in the success of native species related to the variation in weed species, soil and drainage conditions within the one location, indicates the importance of site trials in determining the most successful strategies for restoration. Under the conditions of the field trial, where soil moisture was not a limiting factor, direct seeding proved most successful in drier plots where weed control was prolonged by the combination of weed removal and grazing by native and introduced herbivores. However selective grazing on seedlings grown in tubestock was observed at the field site, so, although grazing of weeds facilitated native seedling emergence, protection from grazing may be needed 1 to 2 years after sowing when seedlings have reached a
height above the grass sward. Direct seeding trials in central NSW (Geeves et al. 2008)
also observed that macropod damage appeared to have its major effect on the growth of seedlings rather than survival. The broader implication of these findings is that
successful direct seeding on sites where weed competition is a limiting factor on native emergence can be achieved when pre-sowing weed control is sustained by macropod grazing, although, once seedlings have established, protection from grazing may be needed facilitate greater growth.
Poor emergence of Eucalyptus obliqua and Allocasuarina seedlings from seed indicated
that, even with ground preparation, it is difficult to produce suitable microsite conditions within improved pasture for native species germination. The results from the direct
seeding trial indicate the importance of identifying the combination of factors limiting native reestablishment before implementing a restoration strategy over a wider area. At the current site implementing large scale direct seeding is likely to result in high ratios of
Acacia to Eucalyptus, resulting in reconstructed vegetation which does not biologically
or structurally represent the native forest being restored.
Where greater levels of intervention are needed, such as reintroducing native seedlings, this generally corresponds with a greater investment in resources. Therefore site specific information is necessary to determine how best to allocate resources. In the current study, ascertaining the native vegetation communities which were present prior to agricultural disturbance was of great importance for setting restoration goals for each of the dominant weed communities present at the site. The variety of floristic, soil and drainage conditions of the different weed communities indicated that successful restoration needed to use species whose natural distribution range matches the site conditions.
The results from the seedling reintroduction trial (Chapter 4) clearly demonstrated that allocating resources to growing seedlings from locally sourced seeds, and planting seedlings in sites that correspond to its ecological range, can result in successful seedling performance irrespective of the use of weed control. Thus, on a site where weed
competition is a limiting factor on native recruitment, this competition can be overcome, without the cost of weed control, by selecting species that suit the site conditions. However, basing species selection on natural ecological ranges may not be successful on sites which have been greatly modified from pre-disturbance conditions, for example, where areas are affected by dryland salinity, and reconstruction may need to rely on using species with specific tolerances to the new conditions.
Where the task of restorationists is to initiate successional development by replanting with native species the restoration of understorey species is usually left to secondary succession. There is thus a need for experimental work to determine whether the recovery of sclerophyll forest on abandoned farmland can be accelerated by the
simultaneous re-introduction of tree, shrub and groundcover species. At the current
restoration site it was found that Eucalyptusobliqua seedling performance can be
facilitated when planted in mixtures with Allocasuarina littoralis. Furthermore, the
results of the experiment implied that sequential planting of species mixtures may produce even more successful results through complementary use of resources. Due to the complexities of interactions involved in species mixtures more research is needed in different environments and with mixtures that contain a greater complement of species to predict the success of planting mixtures under different conditions. However, the present research does show that the simultaneous planting of species mixtures may be an efficient means of accelerating the recovery of sclerophyll forest biodiversity and
structure through ameliorating soil conditions and depressing weed growth.
The present study has also demonstrated that, where the landscape has been modified (i.e. improved pasture), experiments can help determine how best to reintroduce the native species and that this work has the potential to inform restoration strategies that can consistently work over a wider geographic range.