As an inevitable consequence of increased environmental degradation and anticipated future environmental change, societal demand for ecosystem restoration is rapidly increasing. Here, I evaluate ...successes and failures in restoration, how science is informing these efforts, and ways to better address decision-making and policy needs. Despite the multitude of restoration projects and wide agreement that evaluation is a key to future progress, comprehensive evaluations are rare. Based on the limited available information, restoration outcomes vary widely. Cases of complete recovery are frequently characterized by the persistence of species and abiotic processes that permit natural regeneration. Incomplete recovery is often attributed to a mixture of local and landscape constraints, including shifts in species distributions and legacies of past land use. Lastly, strong species feedbacks and regional shifts in species pools and climate can result in little to no recovery. More forward-looking paradigms, such as enhancing ecosystem services and increasing resilience to future change, are exciting new directions that need more assessment. Increased evidence-based evaluation and cross-disciplinary knowledge transfer will better inform a wide range of critical restoration issues such as how to prioritize sites and interventions, include uncertainty in decision making, incorporate temporal and spatial dependencies, and standardize outcome assessments. As environmental policy increasingly embraces restoration, the opportunities have never been greater.
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BFBNIB, INZLJ, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK, ZRSKP
Grasslands, which constitute almost 40% of the terrestrial biosphere, provide habitat for a great diversity of animals and plants and contribute to the livelihoods of more than 1 billion people ...worldwide. Whereas the destruction and degradation of grasslands can occur rapidly, recent work indicates that complete recovery of biodiversity and essential functions occurs slowly or not at all. Grassland restoration—interventions to speed or guide this recovery—has received less attention than restoration of forested ecosystems, often due to the prevailing assumption that grasslands are recently formed habitats that can reassemble quickly. Viewing grassland restoration as long-term assembly toward old-growth endpoints, with appreciation of feedbacks and threshold shifts, will be crucial for recognizing when and how restoration can guide recovery of this globally important ecosystem.
There is widespread evidence that plants can facilitate associated species through microclimate moderation. These effects can act locally, by increasing vital rates via direct effects on the ...conditions experienced by the beneficiary, or at the landscape scale, by enhancing population persistence via environmental heterogeneity and connectivity. Despite linkages between microclimate moderation and the consequences of climate change, few frameworks apply the concepts of facilitation, connectivity, and heterogeneity through this lens. We highlight the utility of expanding current research on facilitators to better understand how their ability to buffer abiotic conditions, promote heterogeneity, and enhance connectivity could shape beneficiaries' response to climate change at multiple scales. We additionally suggest tools and methods for enhanced incorporation of facilitators into models of species response, centered around the integration of facilitator‐moderated microclimates and species responses with the goal of better defining the scenarios under which facilitators could mitigate the effects of climate change. As climates continue to change, the consequences of microclimate moderation at local and landscape scales will become increasingly important to predict, understand, and manage biodiversity response.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Environmental variability can structure species coexistence by enhancing niche partitioning. Modern coexistence theory highlights two fluctuation‐dependent temporal coexistence mechanisms —the ...storage effect and relative nonlinearity – but empirical tests are rare. Here, we experimentally test if environmental fluctuations enhance coexistence in a California annual grassland. We manipulate rainfall timing and relative densities of the grass Avena barbata and forb Erodium botrys, parameterise a demographic model, and partition coexistence mechanisms. Rainfall variability was integral to grass–forb coexistence. Variability enhanced growth rates of both species, and early‐season drought was essential for Erodium persistence. While theoretical developments have focused on the storage effect, it was not critical for coexistence. In comparison, relative nonlinearity strongly stabilised coexistence, where Erodium experienced disproportionately high growth under early‐season drought due to competitive release from Avena. Our results underscore the importance of environmental variability and suggest that relative nonlinearity is a critical if underappreciated coexistence mechanism.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The recognition that a system can appear resilient to changes in the environment, only to reach a critical threshold of rapid and unexpected change, is spurring work to apply threshold models in ...conservation and restoration. Here we address the relevance of threshold models to habitat management. Work to date indicates these concepts are highly applicable: human impacts can widen the range of habitats where threshold dynamics occur and shift communities into new states that are difficult to reverse. However, in many applied settings, threshold concepts are being adopted without evaluation of evidence and uncertainty. We suggest a framework for incorporating threshold models that reflects an emphasis on applicability to decision making and management on relatively short timescales and in human-impacted systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Most ecosystems are now sufficiently altered in structure and function to qualify as novel systems, and this recognition should be the starting point for ecosystem management efforts. Under the ...emerging biogeochemical configurations, management activities are experiments, blurring the line between basic and applied research. Responses to specific management manipulations are context specific, influenced by the current status or structure of the system, and this necessitates reference areas for management or restoration activities. Attempts to return systems to within their historical range of biotic and abiotic characteristics and processes may not be possible, and management activities directed at removing undesirable features of novel ecosystems may perpetuate or create such ecosystems. Management actions should attempt to maintain genetic and species diversity and encourage the biogeochemical characteristics that favor desirable species. Few resources currently exist to support the addition of proactive measures and rigorous experimental designs to current management activities. The necessary changes will not occur without strong input from stakeholders and policy makers, so rapid information transfer and proactive researchâmanagement activities by the scientific community are needed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Understanding priority effects, in which one species in a habitat decreases the success of later species, may be essential for restoring native communities. Priority effects can operate in two ways: ...size‐asymmetric competition and creation of “soil legacies,” effects on soil that may last long after the competitive effect. We examined how these two types of priority effects, competition and soil legacies, drive interactions between seedlings of native and exotic California grassland plants. We established native and exotic communities in a mesocosm experiment. After 5 weeks, we removed the plants from half the treatments (soil legacy treatment) and retained the plants in the other half (priority effect treatment, which we interpret to include both competition and soil legacies). We then added native or exotic seed as the colonizing community. After 2 months, we measured the biomass of the colonizing community. When germinating first, both natives and exotics established priority effects, reducing colonist biomass by 86 and 92%, respectively. These priority effects were predominantly due to size‐asymmetric competition. Only exotics created soil legacies, and these legacies only affected native colonizers, reducing biomass by 74%. These results imply that exotic species priority effects can affect native grassland restorations. Although most restorations focus on removing exotic seedlings, amending soil to address soil legacies may also be critical. Additionally, because native species can exclude exotics if given a head start, ensuring that natives germinate first may be a cost‐effective restoration technique.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
It is increasingly recognized that species distributions are driven by both abiotic factors and biotic interactions. Despite much recent work incorporating competition, predation, and mutualism into ...species distribution models (SDMs), the focus has been confined to aboveground macroscopic interactions. Biotic interactions between plants and soil microbial communities are understudied as potentially important drivers of plant distributions. Some soil bacteria promote plant growth by cycling nutrients, while others are pathogenic; thus they have a high potential for influencing plant occurrence. We investigated the influence of soil bacterial clades on the distributions of bryophytes and 12 vascular plant species in a high elevation talus-field ecosystem in the Rocky Mountain Front Range, Colorado, USA. We used an informationtheoretic criterion (AICc) modeling approach to compare SDMs with the following different sets of predictors: abiotic variables, abiotic variables and other plant abundances, abiotic variables and soil bacteria clade relative abundances, and a full model with abiotic factors, plant abundances, and bacteria relative abundances. We predicted that bacteria would influence plant distributions both positively and negatively, and that these interactions would improve prediction of plant species distributions. We found that inclusion of either plant or bacteria biotic predictors generally improved the fit, deviance explained, and predictive power of the SDMs, and for the majority of the species, adding information on both other plants and bacteria yielded the best model. Interactions between the modeled species and biotic predictors were both positive and negative, suggesting the presence of competition, parasitism, and facilitation. While our results indicate that plant–plant co-occurrences are a stronger driver of plant distributions than plant–bacteria co-occurrences, they also show that bacteria can explain parts of plant distributions that remain unexplained by abiotic and plant predictors. Our results provide further support for including biotic factors in SDMs, and suggest that belowground factors be considered as well.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Niche complementarity, in which coexisting species use different forms of a resource, has been widely invoked to explain some of the most debated patterns in ecology, including maintenance of ...diversity and relationships between diversity and ecosystem function. However, classical models assume resource specialization in the form of distinct niches, which does not obviously apply to the broadly overlapping resource use in plant communities. Here we utilize an experimental framework based on competition theory to test whether plants partition resources via classical niche differentiation or via plasticity in resource use. We explore two alternatives: niche preemption, in which individuals respond to a superior competitor by switching to an alternative, less-used resource, and dominant plasticity, in which superior competitors exhibit high resource use plasticity and shift resource use depending on the competitive environment. We determined competitive ability by measuring growth responses with and without neighbors over a growing season and then used
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N tracer techniques to measure uptake of different nitrogen (N) forms in a field setting. We show that four alpine plant species of differing competitive abilities have statistically indistinguishable uptake patterns (nitrate > ammonium > glycine) in their fundamental niche (without competitors) but differ in whether they shift these uptake patterns in their realized niche (with competitors). Competitively superior species increased their uptake of the most available N form, ammonium, when in competition with the rarer, competitively inferior species. In contrast, the competitively inferior species did not alter its N uptake pattern in competition. The existence of plasticity in resource use among the dominant species provides a mechanism that helps to explain the manner by which plant species with broadly overlapping resource use might coexist.
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BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
Although ecologists have documented the effects of nitrogen enrichment on productivity, diversity and species composition, we know little about the relative importance of the mechanisms driving these ...effects. We propose that distinct aspects of environmental change associated with N enrichment (resource limitation, asymmetric competition, and interactions with soil microbes) drive different aspects of plant response. We test this in greenhouse mesocosms, experimentally manipulating each factor across three ecosystems: tallgrass prairie, alpine tundra and desert grassland. We found that resource limitation controlled productivity responses to N enrichment in all systems. Asymmetric competition was responsible for diversity declines in two systems. Plant community composition was impacted by both asymmetric competition and altered soil microbes, with some contributions from resource limitation. Results suggest there may be generality in the mechanisms of plant community change with N enrichment. Understanding these links can help us better predict N response across a wide range of ecosystems.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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