Downloading the Track Log to Mapinfo

PLEASE NOTE: TWO OF THE FIGURES HAVE BEEN REMOVED FROM THE DIGITAL VERSION OF THIS THESIS DUE TO COPYRIGHT. RESTORATION ECOLOGY IN THE SEMI-ARID WOODLANDS OF NORTH-WEST VICTORIA Fiona Alys Murdoch B.Sc. (Melb), B.Sc.(Hons.) (Syd) This thesis is submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy. School of Science and Engineering University of Ballarat PO Box 663 University Drive, Mt Helen Ballarat, Victoria 3353 Australia Submitted in December, 2005 -ii- Abstract Arid areas are often overgrazed and dysfunctional with poor recruitment of desirable species, diminished control over resources and altered soil properties. Restoration ecology re-establishes these valued processes. State-and-transition models summarise knowledge of vegetation dynamics and tools for restoration, and encourage the incorporation of new information. The model developed here for semi-arid woodlands of north-west Victoria highlighted the unknown cause of observed, natural recruitment and the need for a technique, other than direct seeding and handplanting, for enhancing the recruitment of desirable species. I pursued these knowledge gaps for two dominant, woodland trees: Allocasuarina luehmannii and Casuarina pauper. Natural recruitment of juvenile C. pauper was found to be limited and primarily from root suckers. Extensive recruitment of A. luehmannii was shown to be mostly seedlings established following substantial reductions in grazing pressure since 1996. Seedlings were associated with areas devoid of ground flora near a female tree. The importance of competition between seedlings and ground flora, spatial variation in soil moisture and individual variation in the quantity of seed produced deserves further investigation to enhance future restoration success. Root suckers of both C. pauper and A. luehmannii can be artificially initiated, albeit in low numbers and this was found to be a feasible, new tool for restoration. Suckers are preceded by the growth of callus tissue on exposed or damaged, living, shallow roots. Both male and female trees can produce suckers and spring treatments may be more successful. Genetic fingerprinting of mature A. luehmannii and C. pauper trees in six populations did not identify any clonal individuals indicating that recruitment in the past has been from seedlings. Despite this, the high level of gene flow suggests that the impact of introducing small numbers of root suckers into existing populations is unlikely to impact negatively on the population genetics of these species. - ii - Executive Summary Vegetation dynamics in arid areas are complex and unpredictable. Rainfall is a key driver of positive vegetation change but is infrequent and erratic. Overgrazing has strong negative impacts on landscapes but often, simply reducing grazing pressure does not lead to recovery of the vegetation: active management of the composition of the vegetation community and nutrient and water cycles may also be required. Restoration ecology offers a variety of tools to enable managers to enhance the condition of the vegetation, based around five primary components: reducing grazing pressure, reintroduction of component species, reducing competition from inappropriate species, improving soil properties and increasing control over resources such as water and nutrients. The semi-arid woodlands of north-west Victoria, like many arid landscapes worldwide, are degraded and dysfunctional. There is an increasing interest in options for restoration of these landscapes, particularly in enhancing the recruitment of desirable species. In north-west Victorian national parks, dune reclamation, management of grazing pressure and reintroduction of component species through hand-planting and direct seeding are all conducted with varying degrees of success. This thesis explores and develops theories, models and tools of restoration ecology in arid areas, in particular semi-arid woodlands and the recruitment of two dominant woodland species: Casuarina pauper and Allocasuarina luehmannii. State-and-transition (S-T) models provide a way to summarise knowledge of vegetation dynamics, tools for restoration and the impact of restoration activities. A theoretical S-T framework was developed which shows that vegetation passes through three, increasingly degraded states: loss of component species, dominance of inappropriate species and finally, loss of soil functioning. Restoration must address and reverse these transitions in a step-wise manner. The S-T framework was used to organise the history of degradation and restoration in the semi- arid woodlands of Hattah Kulkyne National Park (HKNP), north-west Victoria. This process highlighted two main opportunities to enhance restoration success. One opportunity was exploring where, when and why natural recruitment of key species was occurring. Some recruitment of C. pauper root suckers was found in Murray Sunset National Park and extensive recruitment of A. luehmannii seedlings was detected in HKNP. The seedlings are believed to have established post-1996 following extensive reductions in grazing pressure and did not appear related to a particular rainfall event. This is contrary to the literature for this species and supports suggestions from others that continuous recruitment of arid plant species is necessary and can occur in the absence of high grazing pressure. The seedlings were associated positively with bare areas within 30 m of a female tree, implying that lack of competition with - iii - ground flora may be significant for their establishment. Although further research is required, better control of annual weeds or replacement with perennial grasses may be necessary to enable the establishment of seedlings following restoration activities. Seedlings were also correlated with topography that increased soil moisture and females trees which produced large quantities of seed. In contrast, variation in seed quality between trees, as determined by germination trials, was not correlated with the occurrence of seedlings although the trials were probably confounded by differing maturity of seed at the time of collection. Dark-colored, mature seed had a higher percentage germination and more rapid germination than light-colored seed. This sends a clear message that care should be taken to only collect mature seed for restoration activities. The second opportunity was developing an alternative tool to enhance the regeneration of desirable species. Direct-seeding and hand-planting experiences a high failure rate due to browsing and low soil moisture. Initiating root suckers of C. pauper and A. luehmannii was investigated because both species are known to produce root suckers and there is evidence from other species that root suckers are better able to establish under these conditions than are seedlings. Although not previously considered in restoration ecology texts, root suckers were found to be a viable tool for restoration. They could be produced in low numbers by damaging and / or exposing shallow roots of male or female trees. There was some indication that spring was likely to be the best season for treatment. No identical genotypes were detected in the genetic fingerprint (Amplified Fragment Length Polymorphisms) obtained for three mature woodlands each of A. luehmannii (82 individuals) and C. pauper (65 individuals). This suggests that historically, seedlings were the predominant mode of recruitment in these species and the presence of numerous juvenile root suckers was attributed to a higher frequency of root disturbance now than historically. However, I believe there would be minimal potential impact of reduced genetic diversity following introduction of root suckers into existing populations. Most genetic diversity was held within the A. luehmannii and C. pauper populations (94.4% and 87.7% respectively) indicating a high level of gene flow. Even small amounts of natural seedling recruitment would be sufficient to restore patterns of genetic variation. Stimulating root suckers also retains genetic diversity because it allows genotypes to persist in the population for longer, thus increasing the probability that they are exposed to conditions conducive to the establishment of seedlings. Nevertheless, a conservative approach is required, aiming for little more than a one to one replacement of existing trees rather than promoting extensive clonal stands. The technique is not viewed as a final solution for the restoration of semi-arid woodlands but rather an emergency measure for degraded woodlands with little natural recruitment. Future research needs in this area are developing a practical tool for broad-scale, mechanised initiation of root suckers in the field. - iv - Additional areas requiring further research, as identified by the S-T model, include understanding and developing techniques to enable regenerating or partially restored woodlands to move to the desirable state of a self-perpetuating, restored woodland. There is also an opportunity to improve the success of direct seeding, and a need to monitor and manage the threat posed by emerging weeds. New information can easily be incorporated into the S-T model developed earlier, demonstrating the utility of the conceptual model. - v - Statement of Authorship Except where explicit reference is made in the text of the thesis, this thesis contains no material published elsewhere or extracted in whole or in part from a thesis by which I have qualified for or been awarded another degree or diploma. No other person’s

Load more