Testing a facilitation model for ecosystem restoration: Does tree planting restore ground layer species in a grassy woodland?

Planning for the restoration of degraded ecosystems has a strong basis in facilitation successional theory, which, as applied in restoration practice, states that planting of structurally dominant tree species will assist the entry of other native species into a restored community. In Australia, tree planting has been widely applied in restoration of grassy woodland ecosystems. Trees have been postulated to reduce the cover and diversity of weed species, thus facilitating recolonization of native woodland species (indirect facilitation). The expected outcomes of this process include reduced species richness and abundance of exotic plant species and increased species richness and abundance/dominance of natives in areas beneath tree canopies, with these trends strengthening with time. To assess whether this was occurring, we carried out a comparative analysis of species assemblages found underneath and outside of planted tree canopies in sites replanted with juvenile canopy tree species 3–5 or 8–10 years previously. We sampled revegetated stands of Cumberland Plain Woodland, an endangered ecological community in Western Sydney, Australia. We found that neither the number nor abundance of native ground layer species beneath canopies increased as a result of trees being planted at sites of both ages. Where seed is limited, we predicted an increase in abundance of existing native species under planted tree canopies. On this point, the results were mixed and showed some natives with an increased abundance while others decreased. Exotic species richness showed the reverse of the expected pattern, being greater under tree canopies. These findings lend no support to the theory of indirect facilitation. We conclude that simple facilitation models may be inadequate to support planning of grassy woodland restoration and that those models incorporating successional time lags and restoration barriers are likely to be more informative about the development of communities initiated by tree planting.     

Developing biodiverse plantings suitable for changing climatic conditions 1: Underpinning scientific methods

Summary Governments across Australia have long been investing in revegetation in an effort to restore biodiversity and, more recently, mitigate climate change. However, no readily available methods have been described to assist project leaders identify species and provenance material likely to be sustainable under the changing climatic conditions of coming decades. Focussing particularly on trees, as trees are important for biosequestration as well as for providing habitat for other native species, Paper 1 of this two part series briefly reviews species distribution models and growth simulation models that could provide the scientific underpinning to improve and refine selection processes. While these previous scientific studies provide useful insights into how trees may respond to climate change, it is concluded that a readily accessible and easy‐to‐use approach is required to consider the potential adaptability of the many trees, shrubs and ground cover species that may be needed for biodiverse plantings. In Part 2 of this paper, the Atlas of Living Australia is used to provide preliminary information to assist species selection by assessing the climatic range of individual species based on their current distributions and, where available, cultivated locations. While using the Atlas can assist current selections, ways are outlined in Part 2 in which more reliable selections for changing climatic conditions could be made, building on the methods described here.     

Testing a Passive Revegetation Approach for Restoring Coastal Plain Depression Wetlands

Restoration of coastal plain depressions, a biologically significant and threatened wetland type of the southeastern United States, has received little systematic research. Within the context of an experimental project designed to evaluate several restoration approaches, we tested whether successful revegetation can be achieved by passive methods (recruitment from seed banks or seed dispersal) that allow for wetland "self-design" in response to hydrologic recovery. For 16 forested depressions that historically had been drained and altered, drainage ditches were plugged to reestablish natural ponding regimes, and the successional forest was harvested to open the sites and promote establishment of emergent wetland vegetation. We sampled seed bank and vegetation composition 1 year before restoration and monitored vegetation response for 3 years after. Following forest removal and ditch plugging, the restored wetlands quickly developed a dense cover of herbaceous plant species, of which roughly half were wetland species. Seed banks were a major source of wetland species for early revegetation. However, hydrologic recovery was slowed by a prolonged drought, which allowed nonwetland plant species to establish from seed banks and dispersal or to regrow after site harvest. Some nonwetland species were later suppressed by ponded conditions in the third year, but resprouting woody plants persisted and could alter the future trajectory of revegetation. Some characteristic wetland species were largely absent in the restored sites, indicating that passive methods may not fully replicate the composition of reference systems. Passive revegetation was partially successful, but regional droughts present inherent challenges to restoring depressional wetlands whose hydrologic regimes are strongly controlled by rainfall variability.     

Spatial distribution and prediction of seed production by Eucalyptus microcarpa in a fragmented landscape

Woodlands worldwide have been greatly modified by clearing for agriculture, and their conservation and restoration requires understanding of tree recruitment processes. Seed production is one possible point of recruitment failure, and one that the spatial arrangement of trees may affect. We sampled 118 Eucalyptus microcarpa (Myrtaceae) trees to compare and analyse the determinants of seed production in this dominant tree of modified, fragmented temperate grassy woodlands, which extend over much of southeastern Australia. Fecundity was estimated as the seed crop measured on leaf mass and whole tree bases and was compared between categories of tree configuration. We also modelled fecundity using boosted regression trees, a new and flexible tool. Fecundity on a leaf mass basis was predominantly influenced by environmental factors (topographic ‘wetness’, slope, soil type), rather than by local tree density and configuration. Fewer seed per unit leaf mass were produced on flat and topographically wet sites, reflecting poor tolerance of waterlogging by E. microcarpa. By contrast, whole tree fecundity was little influenced by environmental factors. Local tree density and configuration did influence whole tree fecundity, which was high in solitary and woodland‐spaced trees and reduced under high local density. We found little evidence for reduced fecundity of E. microcarpa in solitary trees. This points to the importance of scattered trees as sources of seed for tree recruitment and for natural regeneration of landscape level tree cover. Considerable uncertainty remains in modelled seed supply, and may be reduced with sampling across multiple years and greater environmental and spatial domains.     

How far is it to your local? A survey on local provenance use in New South Wales

Summary The decision as to where to source seed is one of the most critical in restoration projects. Locally collected seed is often recommended, or even contractually required, because it is assumed to be adapted to local conditions and therefore result in superior survival and growth rates, conferring a greater probability of restoration success. The perceived advantages, which include retaining the genetic ‘integrity’ of the site, are centred around the avoidance of outbreeding depression and hybridization. These traditional reasons for using locally collected seed need to be reconsidered in the light of rapidly changing climatic and other environmental conditions; plants that are locally adapted now may not be locally adapted in future. Understanding the current usage of local provenance is pivotal to discussions on its appropriateness under climate change. We present the results of a survey of restoration practitioners in New South Wales on attitudes and practices in relation to the use of local provenance. We found that whilst the majority of practitioners preferentially use local provenance seeds, the actual definition of local provenance varied amongst respondents. Whilst 80% of participants believe that projections of future climate change are relevant to restoration projects, there is an apparent reluctance to actively manage for this eventuality. However, many respondents are in favour of a review of seed‐sourcing policy/guidelines to allow for the inclusion of non‐local provenance material. Implications of the survey for potential changes to guidelines to better prepare for anticipated changing conditions are discussed.     

Plant Species Redundancy and the Restoration of Faunal Habitat: Lessons from Plant‐Dwelling Bugs

Restoring disturbed lands is essential for conserving biodiversity. In floristically diverse regions, restoring all plant species following anthropogenic disturbance is financially costly and it is unknown if this can be achieved. However, re‐creating faunal habitat may not require reinstating all plant species if there is a high degree of redundancy. Here, we assess whether there is redundancy among a subset of native plant species chosen to restore fauna habitat following a severe disturbance. Additionally, we determine if reestablished plants support similar faunal assemblages as the same plant species in less disturbed forest. We sampled plant‐dwelling Hemiptera from 1,800 plants across 16 species. We found 190 species of Hemiptera, with most plant species in the forest having distinct hemipteran assemblages. Returning these plant species to areas undergoing restoration reinstated 145 hemipteran species, including the dominant species. Recalcitrant plant species (difficult to propagate and reestablish in restored areas) had different hemipteran assemblages from all other species. There was only one plant species that did not have a distinct assemblage and thus was considered redundant. We conclude that there is little redundancy in this study. For plant‐dwelling Hemiptera (with good powers of dispersal) to recolonize restored areas, restoration efforts will need to reinstate at least 13 of the 16 species of host plant of appropriate age and structure. Consequently, to meet the goal of restoring fauna habitat when there is no knowledge of which plant species are redundant, restoration projects should aim to reinstate all plant species present in less disturbed reference areas.