Tanya G. Bailey

Effect of forest fragmentation and altitude on the mating system of Eucalyptus pauciflora (Myrtaceae)

Habitat fragmentation is a key factor causing variation in important mating system parameters in plants, but its effect is variable. We studied mating system variation among 276 native trees from 37 populations of Eucalyptus pauciflora from Tasmania. We assayed 10 microsatellite loci from 1359 open-pollinated progeny from these trees. Across Tasmania the species’ mating system was characterised by a high outcrossing rate (tm = 0.90) but moderate bi-parental inbreeding (tm–ts = 0.16) and moderate correlated paternity (rP = 0.20) in comparison to other eucalypt species. Despite significant differences in outcrossing rate and correlated paternity among populations, this variation was not correlated with fragmentation. Nevertheless, fragmentation was inversely correlated with the number of germinants per gram of seed capsule content. Outcrossing rate had been reported previously to decrease with increasing altitude in mainland populations of E. pauciflora, but this was not the case in Tasmania. However, a small but significant decrease in correlated paternity occurred with increasing altitude and a decrease in bi-parental inbreeding with increasing altitude was evident in fragmented populations only. It is argued that strong, but incomplete self-incompatibility mechanisms may buffer the mating system from changes in population density and pollinators. While seed yields from highly fragmented populations were reduced, in most cases the seed obtained is unlikely to be more inbred than that from non-fragmented populations and, thus, is likely to be as suitable for use in local forest restoration.

Climate adaptation and ecological restoration in eucalypts

Eucalypts are the cornerstone of ecological restoration efforts across the highly modified agricultural landscapes of southern Australia. ‘Local provenancing’ is the established strategy for sourcing germplasm for ecological restoration plantings, yet this approach gives little consideration to the persistence of these plantings under future climates. This paper provides a synopsis of recent and ongoing research that the authors are undertaking on climate adaptation in eucalypts, combining new genomic approaches with ecophysiological evidence from provenance trials. These studies explore how adaptive diversity is distributed within and among populations, whether populations are buffered against change through capacity for phenotypic plasticity, and how this informs provenancing strategies. Results to date suggest that eucalypts have some capacity to respond to future environmental instability through adaptive phenotypic plasticity or selection of putatively adaptive alleles. Despite this, growing evidence suggests that eucalypts will still be vulnerable to change. Provenancing strategies that exploit adaptations found in non-local provenances could thus confer greater climate-resilience in ecological restoration plantings, although they will also need to account for potential interactions between climate adaptations and other factors (e.g. cryptic evolutionary variation, non-climate-related adaptations, herbivory and elevated CO2).

Early seedling establishment on aged Tasmanian tin mine tailings constrained by nutrient deficiency and soil structure, not toxicity

Revegetation of exposed wastes at historically abandoned mines is frequently constrained by inherent characteristics of poorly developed and contaminated soils. We tested whether the establishment of seedlings on 85-year-old arsenic rich tailings deposits at an abandoned tin mine in north-east Tasmania was limited by toxicity, nutrient limitation or structural factors. We conducted soil analyses, and tested growth of six native species in pot studies utilising both fertiliser treatments and a replacement series involving tailings and potting medium. An in situ three-year field trial was also conducted to assess the effects of adding sand, compost and biochar on plant growth and water infiltration. Analyses of the tailings identified a finely laminated structure and potential manganese, magnesium and potassium deficiencies. There was no evidence of microbial inhibition or adverse metals toxicity, pH or salinity effects. The pot trial indicated nutrient limitation acting on each of the species tested. Physical amendment within the field trial resulted in a highly significant and sustained improvement in infiltration rate, as well as improved growth in three of the six species tested. We conclude that the correction of nutritional and physical deficiencies in surface soils should overcome limitations to the early establishment of native seedlings at this site. This study shows that systematic site assessment and targeted trials is a valuable first step in the revegetation of previously recalcitrant sites.

Stable states in soil chemistry persist in eucalypt woodland restorations

Aim: To assess whether restoration of dry eucalypt-dominated plant communities on ex-pasture sites is constrained by soil characteristics. Location: Central Tasmania, Australia. Methods: We use nutrient status to test recovery trajectories of soils within eucalypt woodland restorations established on ex-pasture sites. Eucalyptus trees within these sites have been successfully established but understorey plant communities have had negligible recovery. Soils from restoration sites, aged from 3 to 22Â years, were contrasted with those from two reference ecotypes: established pastures and native eucalypt woodlands presumed to be similar to that originally replaced by the pastures. We hypothesized that (a) total soil carbon to nitrogen ratios (C:N) would be substantially higher in forest soils than in pasture soils; (b) soil nutrient levels would be lower in forest sites than within pasture sites; and (c) if restoration soils were recovering they should fit between these continuums according to age of planting. Results: Woodland and pasture reference soils were highly constrained in soil C:N and conformed to expectations. However, ex-pasture restoration sites retained the characteristically low C:N and high nutrient levels of pasture soils, in particular total N. They also failed to demonstrate a transformational effect with age of planting. Conclusions: The results suggest that both restoration interventions and natural processes had not sufficiently disrupted existing below-ground systems within the given time frame. Such an intractable stable state within the soil system highlights the need within restoration practice for an increased emphasis on soil ecological transformation. Improving and implementing practices aimed at driving soil change may assist a timelier reassembly of complex native ecosystems. This study also shows that soil C:N ratios may provide a cheap and simple means of identifying soil constraints on restoration.