Resource Management and Geography - Theses
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ItemEnvironmental determinants influencing woody plant persistence: implications for wetland forest restoration using ‘infill’ planting and ‘cryptic’ planting( 2016)Background: Wetlands around the world are in a state of decline due to various processes that threaten wetland cover, soil and water quality, and hydrological flow. To aid the recovery of these threatened ecosystems, large-scale revegetation programs have been undertaken in south-east Australia. ‘Infill’ planting, planting within canopy gaps, and ‘cryptic’ planting, hiding plants within the outer foliage of unpalatable plants, are two revegetation methods used by land managers, and are based on gap dynamics and plant associational effects respectively. However, little is known about the efficacy of these techniques in wetland forests, particularly with respect to flooding, canopy cover and browsing. Question: This study aims to examine the environmental determinants influencing woody plant persistence at infill and cryptic planted sites, and to more specifically determine the effectiveness of cryptic planting to deter browsing. Location: Wetland forests in Yellingbo Nature Conservation Reserve (Victoria, Australia) Methods: To examine environmental determinants, I surveyed 352 two-year-old revegetated plants consisting of Eucalyptus camphora, Melaleuca squarrosa, and Leptospermum lanigerum, across three wetland forest sites in flooded and non-flooded areas. For each surveyed plant, the percentage of canopy cover, presence of flooding, whether the plant was cryptically planted or not, plant height and browsing damage were recorded. To further assess cryptic planting, a trial was established whereby 144 six-month-old tubestock of the same three species were cryptically and non-cryptically planted at the same sites and left for four weeks before being scored for browsing damage. Results: Survey results showed that flooding increased L. lanigerum plant height; cryptic planting increased M. squarrosa plant height and decreased browsing damage, and the interaction between cryptic planting and flooding influenced E. camphora plant height. E. camphora plants were particularly vulnerable to browsing damage, experiencing a mean 77% biomass loss across all surveyed sites. Overall, canopy cover had a weak influence on plant height and browsing damage. Furthermore, the results of the trial showed that cryptic planting reduced browsing of woody plants by 33% for E. camphora, 20% for L. lanigerum, and 12% for M. squarrosa. Conclusions: Various environmental determinants influence the plant height and browsing damage to woody species at infill and cryptically planted sites in wetland forests, with browsing appearing to be a key underlying determinant of plant persistence, particularly for the highly palatable E. camphora. The results of the trial suggest that cryptic planting can be used to reduce, but not prevent the browsing of revegetated plants. However, the suitability of these methods at a site needs to be carefully evaluated before they are implemented, especially in areas of severe browsing. Overall, the knowledge from this study improves our understanding of factors that influence the persistence of revegetated plants in wetland forests, provides support for plant associational defence, as well as evidence for land managers on the effectiveness of these revegetation methods.