Date of Award
Master of Science
Faculty of Communications, Health and Science
Eddie Van Eten
The agricultural region in the central Avon catchment is declining in both arable land and native vegetation. This decline has been due to the clearance of large tracts of native vegetation and its subsequent replacement by exotic crops and pasture species. The loss of vegetation has led to regional land degradation in the form of soil erosion and land salinisation. Therefore, changes in land management practices are required to make agricultural production more compatible with land conservation. Revegetation using native plants is the only management solution that integrates both land and ecological conservation with agricultural productivity. The continuation of current agricultural land use will therefore depend on the development of effective methods of revegetation. The land manager predominantly has a choice between directly sowing seeds and or planting nursery seedlings as methods of revegetation on degraded land. The widespread problem of land degradation in the Avon catchment dictates that the revegetation method chosen must be effective in terms of both seedling establishment and cost on a broad scale. To determine which method is most effective in revegetation, a series of laboratory and field trials were conducted. A trial was conducted in seed germination incubators to determine the relative importance of genetic and environmental influences on seed viability. The genetics of the seed stock had a significant influence on germination between different biolocalities. Similarly, environmental factors such as different temperature regimes also had a significant influence on seed germination. Consequently, a relationship was established between optimum germination temperature and the average mean winter temperature of the biolocality where the seed was collected. This suggests that temperature may influence seed genetics and subsequent germination, which varied according to the biolocality. The identification of environmental parameters that influenced seed germination provided a basis for comparison between direct seeding versus planted nursery seedlings in the field. The number of seedlings established in the second and third year at York was greater for direct seeding than from planted nursery seedlings with the exception of two species belonging to the Leguminosae family. However, the failure of seedlings from either method to become established in the field at Tammin emphasised the need to employ a post-sowing and planting management programme. The costs of seedling establishment using the direct seeding method was approximately one sixth the cost of nursery seedlings with the exception of Kennedia prostrata. The cost and time invested in revegetation programmes necessitates that the optimum seed biolocality should be selected in order to produce the most effective plant establishment from direct seeding in the field. Biolocality selection based on geographical distance alone did not produce conclusive criteria for effective revegetation. However, the matching of biogeographical regions and climatic conditions with the site of revegetation produced the most effective plant establishment. This predominantly resulted in the selection of a local species but in some situations biolocalities from further afield with a similar climate, also proved effective. The invasion of weeds at both the York and Tammin trial sites emphasise the potential effects on the establishment of native vegetation. The growth (height & stem width) of nursery seedlings was significantly reduced while the growth height decreased and the mortality of direct seeded seedlings increased when subjected to weed competition. Reversing the trend in land and ecological degradation within the central Avon catchment can only be achieved through a revegetation programme that integrates nature conservation with agricultural productivity. Direct seeding is a cost effective method of plant establishment provided that adequate attention is given to pre-seed treatment, seed quality testing, selection of the optimum seed biolocality, soil contour and profile preparation and post sowing control of both weed and predators. However, revegetation of degraded land using nursery seedlings can be just as effective when the cost of seed is expensive and difficult to germinate. If the central Avon wheatbelt is to continue to function as the 'bread bowl' of Western Australia then the establishment of native vegetation can only be achieved through the use of direct seeding methods on a broad scale. Current land management practises and the conservation of the remaining remnant vegetation will not maintain a sustainable agricultural based economy or adequately represent existing biodiversity in the central Avon catchment.
Bartholomew, S. J. (1998). Evaluation of revegetation techniques used on degraded agricultural land in the Central Avon Catchment, Western Australia. Retrieved from http://ro.ecu.edu.au/theses/1433