Applied phosphorus has long-term impacts on vegetation responses in restored jarrah forest

Nutrient enrichment can result in long-term negative impacts on a range of native and semi-native plant communities worldwide. Despite this knowledge, fertiliser application is generally viewed as a necessary step in re-establishing native plant communities in post-mining restoration. However, long-term effects of nutrient addition to restored plant communities, particularly in native ecosystems that are adapted to inherently low-nutrient soils, have received little attention. Here we report results of two experiments run for 15 and 20 years, respectively, to investigate the effect of applied P fertiliser on responses of Eucalyptus marginata (jarrah) forest re-sprouter understorey species in sites restored after bauxite mining in Western Australia. Re-sprouter species are abundant in unmined forest but are under-represented in restored sites. At the end of the two experiments (i.e. after 15 and 20 years), the abundance of three groups of re-sprouter understorey species was reduced, compared with the zero-fertiliser treatment, when P fertiliser was applied at rates from 20 to 120 kg P ha-1. In both experiments, the cover associated with P responsive legumes increased with increasing P application rates. This result suggests that when fertiliser is applied, slow-growing re-sprouter species are susceptible to being outcompeted by more vigorous understorey species. Consequently, if the goal of restoration is to re-establish a diverse plant community, then minimising fertiliser application rates may be appropriate

Enduring effects of large legumes and phosphorus fertiliser on jarrah forest restoration 15 years after bauxite mining

Restoring nutrients lost in the mining process and re-establishing nutrient-cycling are often key goals of mine restoration. One common strategy to facilitate these goals is to seed fast-growing legumes combined with one application of P-fertiliser to maximise legume growth and increase soil-N. However, the longer term effects of this strategy have received little attention. Here we report the results of a 15-year-old experiment that was established to test the effects of fertiliser-P application and seeding large understorey legumes, both singly and in combination, on jarrah forest restoration after bauxite mining. Fifteen years after the establishment of this experiment, the majority of the seeded legumes had senesced, with total legume cover having declined significantly compared with results of the same experiment at 5-years-of-age. Yet, despite the legumes having senesced there were still negative effects of both large legumes and P-fertiliser on species richness and abundance of non-leguminous understorey species. These negative effects may be mediated by the persistent effects of legume competition that was evident at 5 years and the accumulation of significant quantities of leaf litter and fine woody debris in the large legume × P-addition treatments. Compared with the 0 kg P ha−1 treatment, application of 20 kg P ha−1 significantly increased jarrah tree growth, but there was no additional benefit of 80 kg P ha−1. These data suggest that moderation of P-fertiliser and large understorey legumes could maximise understorey cover, tree growth and understorey species richness, and therefore simultaneously address multiple key restoration goals

Advances in restoration ecology: rising to the challenges of the coming decades

Simultaneous environmental changes challenge biodiversity persistence and human wellbeing. The science and practice of restoration ecology, in collaboration with other disciplines, can contribute to overcoming these challenges. This endeavor requires a solid conceptual foundation based in empirical research which confronts, tests and influences theoretical developments. We review conceptual developments in restoration ecology over the last 30 years. We frame our review in the context of changing restoration goals which reflect increased societal awareness of the scale of environmental degradation and the recognition that inter-disciplinary approaches are needed to tackle environmental problems. Restoration ecology now encompasses facilitative interactions and network dynamics, trophic cascades, and above- and below ground linkages. It operates in a non-equilibrium, alternative states framework, at the landscape scale, and in response to changing environmental, economic and social conditions. Progress has been marked by conceptual advances in the fields of trait-environment relationships, community assembly, and understanding the links between biodiversity and ecosystem functioning. Conceptual and practical advances have been enhanced by applying evolving technologies, including treatments to increase seed germination and overcome recruitment bottlenecks, high throughput DNA sequencing to elucidate soil community structure and function, and advances in satellite technology and GPS tracking to monitor habitat use. The synthesis of these technologies with systematic reviews of context dependencies in restoration success, model based analyses and consideration of complex socio-ecological systems will allow generalizations to inform evidence based interventions. Ongoing challenges include setting realistic, socially acceptable goals for restoration under changing environmental conditions, and prioritizing actions in an increasingly space-competitive world. Ethical questions also surround the use of genetically modified material, translocations, taxon substitutions, and de-extinction, in restoration ecology. Addressing these issues, as the Ecological Society of America looks to its next century, will require current and future generations of researchers and practitioners, including economists, engineers, philosophers, landscape architects, social scientists and restoration ecologists, to work together with communities and governments to rise to the environmental challenges of the coming decades

Initial conditions can have long-term effects on plant species diversity in jarrah forest restored after bauxite mining

Much of the remarkable plant species diversity of the Southwest Australian Floristic Region can be attributed to high diversity of the understorey in its forests and woodlands, including 400–600 understorey species per km2 in the Northern Jarrah Forest alone. Consequently, returning species diversity is a key challenge for postmining ecological restoration in the region. Each year, Alcoa of Australia undertakes restoration of mined areas within the Northern Jarrah Forest with a goal of returning a self-sustaining jarrah forest ecosystem. To meet this goal, it is important to understand long-term (i.e. > 20 years) trajectories of vegetation development and the restoration practices that direct species diversity outcomes. Here, we report the results of several experiments, the oldest of which is 45 years of age, which together demonstrate significant longer-term effects on understorey species diversity of restoration practices determining initial conditions including topsoil handling, fertiliser application, seeding rates of large legumes, and tree (overstorey) species stocking rates. Our research highlights (1) that ‘historical contingency’ can determine the trajectory of jarrah forest restoration and (2) that longer-term studies are critical as they give a different, sometimes conflicting, perspective to short-term datasets. Notably, after 27 years, we found an inverse relationship between plant cover and P fertilisation, where plant cover was highest in the in the absence of P fertiliser and lowest at the uppermost P amendment rate. We also found that the long-accepted Initial Floristics Model of succession does not fit well with our data. Our overall findings are likely useful to restore understorey diversity to woodlands, forests, and abandoned farmlands elsewhere in the region

First cryo-scanning electron microscopy images and X-ray microanalyses of mucoromycotinian fine root endophytes in vascular plants

Aims. Arbuscule-producing fine root endophytes (FRE) (previously incorrectly Glomus tenue) were recently placed within subphylum Mucoromycotina; the first report of arbuscules outside subphylum Glomeromycotina. Here, we aimed to estimate nutrient concentrations in plant and fungal structures of FRE and to test the utility of cryo-scanning electron microscopy (cryoSEM) for studying these fungi. Methods. To do so, we used replicated cryoSEM and X-ray microanalysis of heavily colonized roots of Trifolium subterraneum. Results. Intercellular hyphae and hyphae in developed arbuscules were consistently very thin; 1.35 ± 0.03 µm and 0.99 ± 0.03 µm in diameter, respectively (mean ± SE). Several intercellular hyphae were often adjacent to each other forming ‘hyphal ropes’. Developed arbuscules showed higher phosphorus concentrations than senesced arbuscules and non-colonized structures. Senesced arbuscules showed greatly elevated concentrations of calcium and magnesium. Conclusions. While uniformly thin hyphae and hyphal ropes are distinct features of FRE, the morphology of fully developed arbuscules, elevated phosphorus in fungal structures, and accumulation of calcium with loss of structural integrity in senesced arbuscules are similar to glomeromycotinian fungi. Thus, we provide evidence that FRE may respond to similar host-plant signals or that the host plant may employ a similar mechanism of association with FRE and AMF

Phosphorus supply affects seedling growth of mycorrhizal but not cluster-root forming jarrah-forest species

Aims Fertiliser is often used to kick-start ecological restoration despite growing evidence of the potentially negative impacts on plant diversity. Jarrah (Eucalyptus marginata) forest species growing on nutrient (especially phosphorus) impoverished soils in southwestern Australia have a suite of adaptations for phosphorus (P) acquisition, including the formation of cluster roots, and associations with mycorrhizal fungi. Here we investigated how escalating P supply, along with a stoichiometric adjustment of nitrogen (N) supply, impacted the growth and nutrition of a wide range of jarrah forest seedlings. Methods In a pot experiment, we measured seedling biomass and nutritional responses of 12 jarrah forest species to a gradient of P supply in relation to N supply, and for the mycorrhizal species, inoculation with arbuscular mycorrhizal fungi. Results Three cluster-root forming species did not respond to increasing P, probably because they were reliant on seed P. Generally, mycorrhizal species showed a positive biomass response to increasing P when N was available. Mycorrhizas benefited seedling growth at low P (9 mg P added per kg of jarrah forest soil) when N was also available, and were parasitic to seedling growth at high P (243 mg P/ kg soil) without additional N. Conclusions These results highlight importance of P and N supply in determining the nature of the symbiosis between plants and mycorrhizal fungi. Since P supply has the potential to reduce plant growth, for a range of species, our results suggest careful consideration of fertiliser amounts for ecological restoration of ecosystems adapted to nutrient poor soils

Nutrient enrichment diminishes plant diversity and density, and alters long-term ecological trajectories, in a biodiverse forest restoration

Nutrient enrichment can negatively affect natural plant communities and result in the loss of species diversity and productivity. Despite this, fertiliser (especially phosphorus) is typically applied to restore highly biodiverse communities. Long-term effects of nutrient addition to restored plant communities, particularly those adapted to inherently low nutrient soils, have received little attention. We report results of a large-scale 20-year field experiment established in West Australian jarrah forest restored after bauxite mining Three P-application rates were applied (0, 80 and 120 kg ha−1) once at the beginning of the experiment, and plant communities monitored after 1, 6, 13 and 20 years. One year after the onset of restoration, native plant species richness and plant density was highest at 80 and 120 kg P ha−1. Subsequently, native species richness, plant density, and the richness and density of seeder and slow-growing resprouter species were highest without fertilisation, establishing the negative impact of P enrichment on plant community and ecosystem development in P impoverished soils. Total plant cover was similar for all P treatments across the chronosequence which, when combined with higher stem densities at zero P, suggests zero P favoured smaller, slower growing species. Applied-P initially favoured weeds and ephemerals and, while these species declined over time, other species were lost from these plots. The similarity of the restored communities to unmined reference jarrah forest increased over time and was consistently highest at in the absence of P fertiliser. Jarrah forest restoration is assumed to follow the initial floristic model of plant succession. However, we question this assumption and instead suggest that successional outcomes are contingent on P fertilisation rather than initial floristics per se. Applied P retarded recruitment of resprouter species that were present at zero P, debunking the assumption under IFM that these species do not disperse to restored areas. Consequently, based on the most comprehensive long-term study of P-fertilisation in the context of restoration of P-impoverished ecosystems yet reported, we propose that P limitation is important for the recreation of species diversity in inherently P impoverished forests. These results highlight the necessity of long-term experiments for understanding forest successional dynamics and implications for restoration practices