Factors limiting the recruitment of Eucalyptus salmonophloia F. Muell. (Salmon gum)

Woodlands dominated by Eucalyptus salmonophloia F. Muell. occur throughout the fragmented landscape of the Western Australian wheatbelt. In most of these remnant woodlands there is no regeneration of E. salmonophloia and this has become a concern for the conservation of biodiversity in the region. The research reported in this thesis contributes to solving this problem firstly by describing aspects of E. salmonophloia's life history, and secondly by documenting the conditions under which recruitment has occurred in unfragmented populations to the east of the Western Australian wheatbelt. Pattern of flowering, seed production, seed viability, pattern of seed fall, post dispersal seed predation, soil seed reserves and factors affecting germination and establishment were investigated. These studies revealed that E. salmonophloia has a suite of life history characteristics that are common to Eucalyptus spp. which recruit seedlings following fire. In particular during inter-fire periods these include a canopy stored seed reserve; a light seed rain from this reserve; high rates of seed predation by ants following dispersal; the absence of a soil seed reserve; and a low probability of seedling establishment should a seed escape predation and germinate. Given the life history characteristics, the study examined the response of unfragmented E. salmonophloia woodlands to the east of the wheatbelt, to disturbance caused by fires and also floods, windstorms and drought. Woodlands known to have experienced disturbances of these types in the last 50 years were found to have cohorts of similar sized E. salmonophloia saplings, this contrasted with undisturbed woodlands. Sites disturbed either by fire, flood or wind storm during 1991/92 displayed adult tree mortality and extensive seedling establishment; although rates of establishment and survival varied between sites. No regeneration was observed at equivalent undisturbed sites. These results indicate that not only fire but several other types of large scale disturbance facilitate seedling recruitment in E. salmonophloia. Increases in resource availability in the post-disturbance environment were measured and the processes responsible discussed. It is postulated that increased resource availability is, at least in part, responsible for enhanced seedling recruitment. This study suggests that large scale natural disturbances of several types are important drivers of the dynamics of E. salmonophloia woodlands. The known lack of recruitment in remnant woodlands is likely to be due to changes in the disturbance regime and/or changes in the ability of E. salmonophloia to regenerate successfully following disturbance. The effects of fragmentation and surrounding agricultural land use on these processes are discussed. The implications of these findings for management of remnant woodlands are considered and areas for further research are suggested