Enhancing seed-based restoration in south-east Queensland using Australian native species

Abstract

Australia's unique plant diversity is threatened by numerous pressures, such as habitat destruction, land degradation and invasive species. In extreme, but frequent cases of habitat destruction and degradation, this results in deeply eroded and damaged landscapes, making it hard for natural regeneration to take place. Land restoration using Australian native seeds (i.e. seed-based restoration) could be a feasible and effective option for restoring degraded landscapes. Using seeds to restore natural ecosystems has a greater chance of success if the seeds are ready to germinate at the time of sowing or given appropriate environmental conditions. For some species, seed characteristics such as seed fill, viability, and dormancy are critical factors that can reduce the rate and percentage of seeds germinating at any given time and are therefore fundamental to the success of seed-based restoration programs. However, these characteristics are often not known in advance, reducing the predictability and cost-effectiveness of using seeds for restoring eroded and damaged landscapes. To overcome seed germination issues and improve seed-based restoration outcomes, this thesis studies the seed ecology of ten Australian native species (four Poaceae, four Fabaceae and two Asparagaceae) that are commonly used in revegetating degraded landscapes in southeast Queensland. The aim was to understand the environmental cues needed to trigger germination, and how these requirements could be met by artificial means, such as chemical (potassium nitrate, smoke water, gibberellic acid, leaching) and/or mechanical (nicking) pre-treatments. Moreover, the use of seed-enhancing technologies (SET: priming, seed coating and seed cookies) was undertaken to study different methods of delivering the germination-enhancing chemicals (GECs) to seeds, also as a seed delivery method to the restoration site. Finally, restoration trials were undertaken in a degraded landscape by using different soil (topsoil or subsoil), site treatments (cover crop, hydrocompost or control) and seed treatment (seed cookies and control) to identify approaches that could enhance field germination, seedling emergence and establishment. The results from this study show that seed fill and/or dormancy were important factors in achieving seed germination and/or seedling emergence. Poaceae species presented low rates of seed fill (< 50%), with Themeda triandra seed fill of only 8 ± 1%. Dormancy was partly xx LIST OF PLATES Plate 2.1. Biodiversity hotspots located in Australia (marked in green).