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1. Ecological restoration is a global priority that holds great potential for benefiting natural ecosystems, but restoration outcomes are notoriously unpredictable. Resolving this unpredictability represents a major, but critical challenge to the science of restoration ecology. 2. In an effort to move restoration ecology toward a more predictive science, we consider the key issue of variability. Typically, restoration outcomes vary relative to goals (i.e. reference or desired future conditions) and with respect to the outcomes of other restoration efforts. The field of restoration ecology has largely considered only this first type of variation, often focusing on an oversimplified success vs. failure dichotomy. The causes of variation, particularly among restoration efforts, remain poorly understood for most systems. 3. Variation associated with restoration outcomes is a consequence of how, where and when restoration is conducted; variation is also influenced by how the outcome of restoration is measured. We propose that variation should decrease with the number of factors constraining restoration and increase with the specificity of the goal. When factors (e.g. harsh environmental conditions, limited species reintroductions) preclude most species, little variation will exist among restorations, particularly when goals are associated with metrics such as physical structure, where species may be broadly interchangeable. Conversely, when few constraints to species membership exist, substantial variation may result and this will be most pronounced when restoration is assessed by metrics such as taxonomic composition. 4. Synthesis and applications. The variability we observe during restoration results from both restoration context (how, where and when restoration is conducted) and how we evaluate restoration outcomes. To advance the predictive capacity of restoration, we outline a research agenda that considers metrics of restoration outcomes, the drivers of variation among existing restoration efforts, experiments to quantify and understand variation in restoration outcomes, and the development of models to organise, interpret and forecast restoration outcomes.

Despite debates on the real impact of plant invasion on native biodiversity, there remain many situations where exotic invasive plants must be managed and habitats restored. Restoration practices that build on plant community assembly principles could be useful to delay or prevent re-invasion after control, but there are still few syntheses of the biodiversity theory, ecological mechanisms and experimental evidence relevant to invasive plant management, possibly delaying applications. To provide such a synthesis, we review current knowledge on three key determinants of invasion success: biotic resistance, abiotic constraints, and propagule pressure. We elaborate on the ecological mechanisms at play for each determinant and emphasize, using case studies, their relevance for invasive plant management and ecological restoration. We find evidence that restoring a plant cover can enhance invasion resistance, but the challenge for both research and field applications is to understand how multiple determinants interact in relation to species traits in the fields. Failure to recognize these interactions and their effect on community assembly processes may explain some of the mixed species responses observed. While we need control and restoration case studies with local species at different sites, the development of a coherent, dynamic and adaptive framework around biotic/ecological resistance will have to go beyond the idiosyncrasy of the many species and systems being tested. Emphasizing the functional diversity of the restored community seems a promising approach when facing potentially multiple invaders and/or fluctuating abiotic conditions.

1. Recovering biological diversity and ecosystem functioning are primary objectives of ecological restoration, yet these outcomes are often unpredictable. Assessments based on functional traits may help with interpreting variability in both community composition and ecosystem functioning because of their mechanistic and generalizable nature. This promise remains poorly realized, however, because tests linking environmental conditions, functional traits, and ecosystem functioning in restoration are rare. 2. Here, we provide such a test through what is to our knowledge the first empirical application of the 'response-effect trait framework' to restoration. This framework provides a trait-based bridge between community assembly and ecosystem functioning by describing how species respond to environmental conditions based on traits and how the traits of species affect ecosystem functioning. 3. Our study took place across 29 prairies restored from former agricultural fields in southwestern Michigan. We considered how environmental conditions affect ecosystem functioning through and independently of measured functional traits. To do so, we paired field-collected trait data with data on plant community composition and measures of ecosystem functioning and used structural equation modelling to determine relationships between environmental conditions, community-weighted means of functional traits and ecosystem functioning. 4. Environmental conditions were predictive of trait composition. Sites restored directly from tillage (as opposed to those allowed to fallow) supported taller species with larger seeds and higher specific leaf area (SLA). Site age and fire frequency were both negatively related to SLA. We also found a positive relationship between soil moisture and SLA. 5. Both trait composition and environmental conditions predicted ecosystem functioning, but these relationships varied among the measured functions. Pollination mode (animal pollination) increased and fire frequency decreased floral resource availability, seed mass had a negative effect on below-ground biomass production, and vegetative height increased decomposition rate. Soil moisture and fire frequency both increased while site age decreased above-ground biomass production, and site age and soil moisture both increased decomposition rate. 6. Synthesis and applications. Our results suggest that both trait composition and environmental conditions play a role in shaping ecosystem function during restoration, and the importance of each is dependent on the function of interest. Because of this, environmental heterogeneity will be necessary to promote multiple ecosystem functions across restored landscapes. A trait-based approach to restoration can aid interpretation of variable outcomes through insights into community assembly and ecosystem functioning.

Biological invasions resulting from anthropogenic activities are one of the greatest threats to maintaining ecosystem functioning and native biodiversity. Invasions are especially problematic when the invading species behaves as an ecosystem engineer that is capable of transforming ecosystem structure, function, and community dynamics. Of particular concern is the spread of emergent wetland grasses whose root systems alter hydrology and structural stability of soils, modify ecosystem functions, and change community dynamics and species richness. To address the threats posed to ecosystems across the globe, management practices focus on the control and removal of invasive grasses. However, it remains unclear how severely invasive grasses alter ecosystem functions and whether alterations persist after invasive grass removal, limiting our ability to determine if management practices are truly sufficient to fully restore ecosystems. Here, we conducted a meta-analysis to quantify ecological alterations and the efficacy of management following the invasion of Spartina alterniflora and Phragmites australis, two common and pervasive invaders in coastal wetlands. Our results indicate that S. alterniflora and P. australis significantly alter measures of ecosystem functioning and organismal abundance. Invaded ecosystems had significant elevations in abiotic carbon and nitrogen fixation and uptake in areas with invasive grasses, with differential photosynthetic pathways of these two grass species further explaining carbon fluxes. Moreover, evidence from our analyses indicates that management practices may not adequately promote recovery from invasion, but more data are needed to fully assess management efficacy. We call for future studies to conduct pairwise comparisons between uninvaded, invaded, and managed systems and provide research priorities.

1. The outcomes of restoration efforts are contingent on the specifics of the restoration practices utilized, but also on uncontrolled contingencies such as site effects and year effects. Although restoration practitioners have long been aware that the successes of their projects vary from site to site and from year to year, there have been few direct experimental tests of these contingencies. 2. We established grassland restoration plots identically across three sites in northern California, in each of four establishment years (for 12 site-year combinations). 3. The resulting plant communities differed significantly across sites and across establishment years. As a consequence of these community differences, there were 'forb years' and 'grass years', although these sometimes differed among sites. Multivariate analysis identified mean annual temperature and total precipitation as likely drivers of some of these differences. 4. Synthesis and applications. Our results not only confirm the idiosyncratic nature of the results of restoration efforts (and ecological experiments in general) but also demonstrate that some of this variation can potentially be related to measurable environmental conditions. Understanding the drivers of this variability can ultimately aid restoration practitioners by allowing them to focus restoration efforts on years and sites most likely to yield desired outcomes.

In an age of rewilding and dramatic declines in biodiversity, we are developing a new way to reintroduce raptors: parental hacking. The principle behind it is similar to traditional hacking, where the birds are released without contact with adult conspecifics. In parental hacking, our method, the parents feed their own offspring until the end of the post-fledgling dependency period. Our programme aims to reintroduce the white-tailed sea eagle (Haliaeetus albicilla) to the Upper Rhône Basin in France. It started in 2022 and will continue until 2030, with the release of 80 young eagles. We describe the method used in 2022, followed by the improvements made in 2023, and finally compare the two years. The young eagles were raised in aviaries at the reintroduction site by their captive-born parents in the Aigles du Léman Park (Haute-Savoie, France). In 2022, two young females and two young males were released as soon as they were able to fly at the age of three months, but they often ended up on the ground due to a lack of flying ability and attacks from wild black kites (Milvus migrans) defending their territory. Therefore, the young eagles were returned to their parents’ aviary before being released a second time at five months in August 2022. One month after release, one male was already 50 km from the reintroduction site, while the other three stayed close to the park. In 2023, five young females and five young males were released at five months. This came after four weeks in a large training aviary to learn how to fly, perch, and fish. The behaviour of the young eagles after release varied greatly between individuals. Overall, 4 out of 10 young eagles travelled long distances and did not return to the reintroduction site to feed within a month, while the other 6 chose to stay close (within 20 km) to the reintroduction site.

Biodiversity restoration on a landscape level requires people with different backgrounds to connect and collaborate over an extended period of time. Hence, understanding how conservation and restoration goals are negotiated and achieved necessitates an understanding of the dynamics of the social fabric: the social networks and interactions that develop, underpin, and sustain collective action. This paper identifies patterns and factors that have contributed to constructive collaboration for biodiversity in the rural area of Ooijpolder-Groesbeek , which has been at the vanguard of nature and landscape development in the Netherlands. We conducted a historical analysis of the period between 1985 and 2022, based on a broad range of literature and interviews with key actors in the region. We provide a narrative account of the tipping points and the preceding processes that propelled the region to its current state. The emergence of these tipping points is analyzed through the lens of a conceptual framework on the dynamic interplay between practices, social interactions, events, and circumstances. Our findings reveal how an integrative landscape approach, the use of suitable boundary objects, and continuous network building and relation management across various levels have contributed to the success of the collective effort.

1. Predicting restoration outcomes requires an understanding of the natural variability of ecosystem properties. A hierarchy of predictability has been proposed that ranks measures of restoration success from most-to-least predictable in the following order: vegetation structure > taxonomic diversity > functional diversity > taxonomic composition. This hierarchy has not been tested empirically, and the location within the hierarchy of trait-based measures, such as community-level trait means and variances, is not well understood. 2. Our objective was to test the hierarchy of predictability in one of the longest running ecological restoration experiments in the western USA. We used linear mixed effects models to analyse changes in herbaceous biomass, species richness, two functional diversity (FD) indices, community-weighted mean (CWM) traits and taxonomic composition among experimental restoration treatments from 1992 to 2014 in a ponderosa pine-bunchgrass ecosystem. Restoration treatments included combinations of light or heavy tree thinning and no fire or repeated prescribed fire every 4 years to release the herbaceous understorey from overstorey competition. 3. Herbaceous biomass and species richness were the two most predictable and least variable measures of success, whereas taxonomic composition exhibited the highest variability among plots through time. Trait-based measures of FD tended to be more predictable and less variable than CWM trait values in this experiment. Both CWM trait values and FD were less variable among plots than taxonomic composition. 4. Synthesis and applications. Ecosystem properties that are intrinsically more variable over space and time will often be the least predictable restoration outcomes. Restoration practitioners can expect vegetation structure, species richness and functional diversity to be more predictable and less variable than taxonomic composition, which can exhibit dynamic responses to restoration treatments over time. Monitoring dominant native and invasive species will always be important, but given the functional redundancy that can occur within communities, strict targets based on composition may rarely be met. Trait-based metrics that integrate taxonomic composition into their calculation are less variable and potentially more meaningful for evaluating ecosystem responses. The hierarchy of predictability should be tested in a range of ecosystems to determine its generality.

1. Developing restoration strategies that accelerate natural successional processes and are resource-efficient is critical to facilitating tropical forest recovery across millions of hectares of deforested lands in the tropics. 2. We compared tree recruitment after a decade in three restoration treatments (natural regeneration, applied nucleation/island tree planting and plantation) and nearby reference forest in the premontane rain forest zone in southern Costa Rica. The study was replicated at 13 sites with a range of surrounding forest cover, enabling us to evaluate the relative influence of local restoration treatments and landscape forest cover on tree recruitment. 3. Density of small-seeded (<5 mm), animal-dispersed recruits was lower in natural regeneration than in applied nucleation, plantation or reference forest plots. Species richness, species density and density of medium (5-10 mm)- and large (>10 mm)-seeded, animal-dispersed recruits were greatest in reference forest, intermediate in applied nucleation and plantation and lowest in natural regeneration plots. 4. Recruit composition differed substantially between reference forest and all restoration treatments. In general, plantation recruit composition was more similar to reference forests and natural regeneration least similar; however, there was high within-treatment variation. 5. Models suggested weak support for the effect of surrounding forest cover on tropical tree recruit density and composition, as compared to restoration treatment and site conditions (e.g. elevation), in this intermediate forest cover landscape. 6. Synthesis and applications. Applied nucleation appears to be a cost-effective strategy as compared to plantation-style planting to accelerate tropical forest recovery regardless of the amount of forest cover immediately adjacent to the site. However, even with active restoration interventions, forest recovery is a multidecade process that proceeds at highly variable rates.