A. J. Gravina

Structural development of vegetation on rehabilitated North Stradbroke Island: Above/belowground feedback may facilitate alternative ecological outcomes

IntroductionThis study depicts broad-scale revegetation patterns following sand mining on North Stradbroke Island, south-eastern Queensland, Australia.MethodsBased on an ecological timeline spanning 4–20 years post-rehabilitation, the structure of these ecosystems (n = 146) was assessed by distinguishing between periods of ‘older’ (pre-1995) and ‘younger’ (post-1995) rehabilitation practices.ResultsThe general rehabilitation outlook appeared promising, whereby an adequate forest composition and suitable levels of native biodiversity (consisting of mixed-eucalypt communities) were achieved across the majority of rehabilitated sites over a relatively short time. Still, older sites (n = 36) appeared to deviate relative to natural analogues as indicated by their lack of under-storey heath and simplified canopy composition now characterised by mono-dominant black sheoak (Allocasuarina littoralis) reaching up to 60% of the total tree density. These changes coincided with lower soil fertility parameters (e.g., total carbon, total nitrogen, and nutrient holding capacity) leading us to believe that altered growth conditions associated with the initial mining disturbance could have facilitated an opportunistic colonisation by this species. Once established, it is suspected that the black sheoak’s above/belowground ecological behaviour (i.e., relating to its leaf-litter allelopathy and potential for soil-nitrogen fixation) further exacerbated its mono-dominant distribution by inhibiting the development of other native species.ConclusionsAlthough rehabilitation techniques on-site have undergone refinements to improve site management, our findings support that putative changes in edaphic conditions in combination with the competitive characteristics of some plant species can facilitate conditions leading to alternative ecological outcomes among rehabilitated ecosystems. Based on these outcomes, future studies would benefit from in depth spatio-temporal analyses to verify these mechanisms at finer investigative scales.

Seed biology implications for the maintenance and establishment of Tetratheca juncea (Tremandraceae), a vulnerable Australian species

Tetratheca juncea Smith is an endemic and vulnerable shrub species with apparently poor recruitment from New South Wales, Australia. Lack of understanding of seed biology limits management options for promoting survival of existing populations and recruitment of new populations. This study investigated the soil seed bank, seed viability, germination and seed dormancy. The plants release seeds in January but no seeds germinated from soil collected near the plants in September 1999, irrespective of the soil being treated by smoke, heat or fire. When sampled again in February 2001, seeds were present in the soil seed bank but were not viable. Viability testing of seeds collected from the plants determined that at least a third of the seeds being produced were viable, even after storage for 6 months. Seed germination and dormancy investigations found that the seeds germinated following exposure to smoke or scarification of the seed coat. Untreated seeds did not germinate during the preliminary study, although a proportion of untreated seeds germinated from a later seed lot. Fire management is important for promoting the survival of this species and the soil seed bank cannot be relied on for re-establishment of populations as the longevity of the soil seed bank seems to be short. Many other species of Tetratheca are also rare or threatened and this study suggests that hand-collected seeds treated with fire-related stimuli may be important for re-establishing those species and that the soil seed bank requires assessment before being relied on as a source of propagules or for maintaining a population.