Establishment of perennial shrub and tree species in degraded Eucalyptus salmonophloia (Salmon gum) remnant woodlands:: Effects of restoration treatments

Woodlands dominated by Eucalyptus salmonophloia (salmon gum) occur throughout the fragmented landscape of the southwestern Australian wheatbelt. These remnants are often degraded by livestock grazing and weed invasion and in many cases there is little or no understorey remaining and little or no regeneration of the dominant tree E. salmonophloia. There is a growing interest in developing techniques for restoring remnant woodlands. This study describes techniques for establishing seedlings of the dominant tree and perennial understorey species in E. salmonophloia (salmon gum) woodlands degraded by livestock grazing. The study tests the hypothesis that, in addition to the exclusion of livestock, management of weeds and reintroduction of plant species, restoration of plant species diversity will require techniques which mimic large-scale disturbances, reduce soil compaction, and restore soil water infiltration to suitable rates. Five-month-old seedlings of the dominant tree E. salmonophloia and four commonly associated woody shrubs (Acacia hemiteles, Atriplex semibaccata, Maireana brevifolia, and Melaleuca pauperiflora) were planted into areas that differed with respect to grazing (-rabbit/-livestock and +rabbit/-livestock), tree canopy disturbance (+/-competition with tree canopy) and amelioration of soil compaction (+/-deep ripping). Following three growing seasons and two summers, the exclusion of rabbits had no significant effect on the survival and growth of planted species. As a consequence grazing treatments are pooled for the purposes of presenting the impacts of removing competition with adult trees and soil deep ripping. The removal of competition with adult E. salmonophloia trees significantly improved the survival of E. salmonophloia seedlings but did not improve survival of understorey species. Deep ripping the soil significantly improved the survival of both E. salmonophloia and the shrub A. hemiteles but did not improve the survival of other understorey species. In contrast to seedling survival, the removal of adult E. salmonophloia trees and deep ripping soil significantly increased the growth of all species. The results indicate that increasing levels of intervention will increase the chances of successfully restoring tree and understorey species diversity in degraded E. salmonophloia woodlands.