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Biochemical properties of soil in forest restoration: A case study of native vegetation within E. globulus plantations in the south west of Western Australia.

Safianowicz, Katarzyna (2013) Biochemical properties of soil in forest restoration: A case study of native vegetation within E. globulus plantations in the south west of Western Australia. PhD thesis, Murdoch University.

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Soil microbial communities play and essential role in nutrient cycling and influence functioning of the ecosystems though taking part in feedback mechanisms that shape plant communities. Anthropogenic influences on vegetation can result in changes in the activity of soil microbes, which is reflected in soil chemical and biochemical properties, for example nutrient content, enzymatic activity or respiration. Such information about microbial function in soils can enhance research focusing on land use change, degradation and restoration.

Large-scale deforestation of land for agricultural use in the south west of Western Australia (SWWA) and subsequent artificial afforestation of resulting pastureland with Eucalyptus globulus plantations created a mosaic of native vegetation remnants, exotic forest and pastures. Remnants of native woodland in such a fragmented landscape are prone to decline, often as a result of the legacy of pastoral uses of the neighbouring land, such as grazing by livestock. Degradation of the remnants undermines the efforts to preserve native biodiversity of the region. Restoration undertaken to improve their condition is usually by herbicide application and planting of native understorey species. To date, little research is available to guide these efforts towards efficient and successful use of scarce resources allocated to rehabilitation in land management projects. The main objective of this study was to determine the usefulness of soil biochemical properties in assessing land degradation and restoration treatments in native vegetation remnants enclosed in E. globulus plantations in SWWA. It was hypothesised that differences in soil biochemical properties detected using microplate assays would allow assessment and monitoring of soil following land use change and potential of restoration treatments. A second objective was to determine which out of the restoration or degradation treatments had the most influence on soil chemical properties as well as on weed cover, native vegetation growth and regeneration in remnant vegetation. The hypotheses tested were that: a) soil nutrient enrichment would be a more influential factor contributing to degradation than clearing and incursion of exotic ryegrass in the remnants with native understorey and b) herbicide application and mulching with plantation harvest residue would improve survival and growth of seedlings planted for revegetation in remnants with exotic understorey. This information is important for informing the plantation companies responsible for managing remnant woodland in their estates, particularly those with forest product certification. A third objective was to find chemical and biochemical properties of soil that were both descriptors and predictors of processes involved in disturbance and restoration to investigate the possibility of developing an inexpensive tool for monitoring the condition of remnant vegetation and assessing the suitability of putative restoration treatments. It was hypothesised that soil functional diversity based on soil chemical and biochemical properties could be used as an indicator of land condition.

The first study revealed that while soils from five land conditions common in the landscapes of SWWA differed in their chemical and biochemical properties, soil physical properties were more influential than soil chemical and biochemical properties. The second study showed that addition of fertilizer, but not clearing of native vegetation or incursion of exotic ryegrass, altered the soil biochemistry in remnant vegetation with native understorey. It also revealed that soil alkaline phosphomonoesterase and β-glucosidase activity and soil respiration in response to succinic, cinnamic and α-ketoglutaric acids were related to the outcomes of disturbance of both native and exotic vegetation. The results of subsequent studies showed, contrary to the expectations, that mulching with plantation harvest residue increased soil nutrient levels, especially potassium and nitrate concentration. Herbicide application and mulching improved the growth and survival of native seedlings planted for revegetation; however, there were species-specific responses to each treatment. Analysis of the relationships among soil chemical and biochemical properties revealed that soil nitrogen pools and pH were most influential on soil biochemistry. Functional diversity varied among soils from different land condition, but not among the experimental treatments applied. Soil nitrate, ammonium, potassium and sulphur, alkaline phosphomonoesterase activity and N-mineralization potential together with respiration in response to imidazole, thiamine and the organic acids: succinic, cinnamic and α-ketoglutaric, were useful in discerning land conditions and experimental treatments.

Microplate assays for soil biochemical properties provided information useful in discriminating among land conditions; however, they were not sensitive enough to clearly detect the effects of all experimental interventions. The usefulness of a soil functional diversity approach as an index for disturbance was tentatively confirmed; however, more work is required to assure its’ robustness and wider applicability.

The importance of soil nitrogen and pH in altering soil biochemical properties found in this study is consistent with previous research. Soil nitrogen was more important than soil phosphorus in maintaining exotic plant incursion in remnant vegetation with native understorey, suggesting that managing nitrogen pools by avoiding excess fertilizer application and encouraging denitrification could be a useful strategy to minimise the weed load in remnant vegetation, one of the biggest impediments to restoration. Mulching with plantation harvest residue with occasional application of glyphosate controlled exotic weeds as effectively as the herbicide-only treatment, while benefiting the survival and growth of the native plant seedlings more, probably through increasing moisture retention and providing nutrients. The choice of restoration treatments have to be considered in conjunction with the choice of plant species used for revegetation.

The usefulness of microplate tests for soil biochemical properties in assessing land condition, including that of remnant vegetation with native and exotic understorey was confirmed. This assay format was used with promising results to show the effects of several treatments simulating degradation and restoration on soils and vegetation, which is of practical importance in management of remnant patches of native vegetation. In addition, it provided preliminary insights into the relationships among soil chemical and biochemical properties, which could contribute to the development of a high through-put, inexpensive and reliable tool for assessing and monitoring land condition and restoration efforts.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): Burgess, Treena, Archibald, Robert and Hardy, Giles
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