Michael P. Perring

Managing the whole landscape: historical, hybrid, and novel ecosystems

The reality confronting ecosystem managers today is one of heterogeneous, rapidly transforming landscapes, particularly in the areas more affected by urban and agricultural development. A landscape management framework that incorporates all systems, across the spectrum of degrees of alteration, provides a fuller set of options for how and when to intervene, uses limited resources more effectively, and increases the chances of achieving management goals. That many ecosystems have departed so substantially from their historical trajectory that they defy conventional restoration is not in dispute. Acknowledging novel ecosystems need not constitute a threat to existing policy and management approaches. Rather, the development of an integrated approach to management interventions can provide options that are in tune with the current reality of rapid ecosystem change.

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.

Does the terrestrial biosphere have planetary tipping points

Tipping points--where systems shift radically and potentially irreversibly into a different state--have received considerable attention in ecology. Although there is convincing evidence that human drivers can cause regime shifts at local and regional scales, the increasingly invoked concept of planetary scale tipping points in the terrestrial biosphere remains unconfirmed. By evaluating potential mechanisms and drivers, we conclude that spatial heterogeneity in drivers and responses, and lack of strong continental interconnectivity, probably induce relatively smooth changes at the global scale, without an expectation of marked tipping patterns. This implies that identifying critical points along global continua of drivers might be unfeasible and that characterizing global biotic change with single aggregates is inapt.

Increased plant growth from nitrogen addition should conserve phosphorus in terrestrial ecosystems

Inputs of available nitrogen (N) to ecosystems have grown over the recent past. There is limited general understanding of how increased N inputs affect the cycling and retention of other potentially limiting nutrients. Using a plant–soil nutrient model, and by explicitly coupling N and phosphorus (P) in plant biomass, we examine the impact of increasing N supply on the ecosystem cycling and retention of P, assuming that the main impact of N is to increase plant growth. We find divergent responses in the P cycle depending on the specific pathway by which nutrients are lost from the ecosystem. Retention of P is promoted if the relative propensity for loss of plant available P is greater than that for the loss of less readily available organic P. This is the first theoretical demonstration that the coupled response of ecosystem-scale nutrient cycles critically depends on the form of nutrient loss. P retention might be lessened, or reversed, depending on the kinetics and size of a buffering reactive P pool. These properties determine the reactive pools ability to supply available P. Parameterization of the model across a range of forest ecosystems spanning various environmental and climatic conditions indicates that enhanced plant growth due to increased N should trigger increased P conservation within ecosystems while leading to more dissolved organic P loss. We discuss how the magnitude and direction of the effect of N may also depend on other processes.

Incorporating novelty and novel ecosystems into restoration planning and practice in the 21st century

Novelty pervades the biosphere. In some cases, potentially irreversible abiotic and/or biotic changes have led to the crossing of thresholds and thus the formation of “novel ecosystems.” Their widespread emergence (particularly on land) and the presence of continued environmental change challenge a traditional restoration goal of restoring an historical ecosystem. Instead, we argue that restoration could broaden its frame of reference to consider how novel ecosystems might be used to maintain global biodiversity and provide ecosystem services and, in doing so, save potentially wasted efforts in attempting to fulfil traditional goals. Here we explore this contention in more depth by addressing: Are novel ecosystems innovative planning or lowering the bar? We show that novel ecosystems were not innovative planning in their original conception. On the contrary, they were recognized as ecosystems that were recalcitrant to traditional restoration approaches, coupled with an awareness that they had arisen inadvertently through deliberate human activity, either on- or off-site. Their recalcitrance to traditional restoration suggests that alternative goals may exist for these ecosystems using sometimes innovative intervention. This management may include biodiversity conservation or restoration for ecological function. We elucidate the latter aspect with reference to an experiment in the wheatbelt of Western Australia—The Ridgefield Multiple Ecosystem Services Experiment—the design of which has been informed by ecological theory and the acceptance of novelty as an ecosystem component. Although novel ecosystems do provide opportunities to broaden restoration planning and practice, and ultimately maintain and conserve global biodiversity in this era of environmental change, they necessarily “lower the bar” in restoration if the bar is considered to be the historical ecosystem. However, in these times of flux, such a bar is increasingly untenable. Instead, careful and appropriate interventions are required at local, regional, and global scales. These interventions need to take history into account, use ecological and evolutionary theory to inform their design, and be mindful of valid concerns such as hubris. Careful interventions thus provide an opportunity for broadening restoration’s framework to focus on maintaining global biodiversity and delivering ecosystem services as well as the traditional goals of restoring historical ecosystems.

Global environmental change effects on ecosystems: the importance of land-use legacies.

One of the major challenges in ecology is to predict how multiple global environmental changes will affect future ecosystem patterns (e.g. plant community composition) and processes (e.g. nutrient cycling). Here, we highlight arguments for the necessary inclusion of land-use legacies in this endeavour. Alterations in resources and conditions engendered by previous land use, together with influences on plant community processes such as dispersal, selection, drift and speciation, have steered communities and ecosystem functions onto trajectories of change. These trajectories may be modulated by contemporary environmental changes such as climate warming and nitrogen deposition. We performed a literature review which suggests that these potential interactions have rarely been investigated. This crucial oversight is potentially due to an assumption that knowledge of the contemporary state allows accurate projection into the future. Lessons from other complex dynamic systems, and the recent recognition of the importance of previous conditions in explaining contemporary and future ecosystem properties, demand the testing of this assumption. Vegetation resurvey databases across gradients of land use and environmental change, complemented by rigorous experiments, offer a means to test for interactions between land-use legacies and multiple environmental changes. Implementing these tests in the context of a trait-based framework will allow biologists to synthesize compositional and functional ecosystem responses. This will further our understanding of the importance of land-use legacies in determining future ecosystem properties, and soundly inform conservation and restoration management actions.

Combining Biodiversity Resurveys across Regions to Advance Global Change Research

More and more ecologists have started to resurvey communities sampled in earlier decades to determine long-term shifts in community composition and infer the likely drivers of the ecological changes observed. However, to assess the relative importance of and interactions among multiple drivers, joint analyses of resurvey data from many regions spanning large environmental gradients are needed. In this article, we illustrate how combining resurvey data from multiple regions can increase the likelihood of driver orthogonality within the design and show that repeatedly surveying across multiple regions provides higher representativeness and comprehensiveness, allowing us to answer more completely a broader range of questions. We provide general guidelines to aid the implementation of multiregion resurvey databases. In so doing, we aim to encourage resurvey database development across other community types and biomes to advance global environmental change research.

Peeking into the black box: a trait‐based approach to predicting plant–soil feedback

Feedbacks between plants and soil communities may be elusive, yet they have far-reaching consequences for plant physiology, competition and community structure. Plant–soil feedbacks (PSFs) are plant-mediated changes to soil properties that ultimately influence the performance of the same or other plants (Van der Putten et al., 2013). These PSFs may be mediated by root-associated organisms (hereafter, root-mediated feedbacks) or saprotrophic organisms and associated litter characteristics (hereafter, litter-mediated feedbacks). However, we know little about the potential mechanistic linkages and relative strengths between these distinct, but connected, processes as root- and litter-mediated feedbacks have generally been studied independently from each other. This is despite the fact that root-associated organisms and saprotrophs can interact through various mechanisms, either directly or as mediated by the plant (e.g. Wardle, 2006). By using a trait-based approach,Ke et al. (in this issue of New Phytologist, pp. 329–341) make an important contribution by integrating root- and litter-mediated PSFs in a nitrogen (N)-based, stage-structured plant population and microbial community model. Their approach allows us to start peeking into the ‘black box’ thereby promoting a better understanding of how PSFs operate interactively. Ke et al. considered various plant traits (e.g. decomposability), but also incorporated trait variation in the physiology, demography and composition of the soil microbial community, and tested their separate and interactive effects on PSF strength in a comprehensive simulation framework. Finally, they used empirical evidence from the literature to support their model predictions.

Removing Phosphorus from Ecosystems Through Nitrogen Fertilization and Cutting with Removal of Biomass

High amounts of phosphorus (P) are in soil of former farmland due to previous fertilizer additions. Draining these residues would provide conditions for grassland plant species diversity restoration amongst other ecosystem benefits. Nitrogen (N) fertilization followed by cutting with subsequent removal of biomass has been suggested as a P residue removal method. We present a general model of N and P ecosystem cycling with nutrients coupled in plant biomass. We incorporate major P pools and biological and physico-chemical fluxes around the system together with transfers into and out of the system given several decades of management. We investigate conditions where N addition and cutting accelerate fertilizer P draining. Cutting does not generally accelerate soil P depletion under short-term management because the benefits of biomass removal through decreased P mineralization occur on too long a timescale compared to cutting’s impact on the ability of plants to deplete nutrients. Short-term N fertilization lowers soil fertilizer P residues, provided plant growth remains N limited. In such situations, N fertilization without biomass removal increases soil organic P. Some scenarios show significant reductions in available P following N addition, but many situations record only marginal decreases in problematic soil P pools compared to the unfertilized state. We provide explicit conditions open to experimental testing. Cutting might have minimal adverse impacts, but will take time to be successful. N fertilization either alone or in combination with cutting is more likely to bring about desired reductions in P availability thus allowing grassland restoration, but might have undesired ecosystem consequences.

Novel ecosystems in ecological restoration and rehabilitation: Innovative planning or lowering the bar?

Stemming from a special symposium at the 2012 inaugural meeting of the Society for Ecological Restoration Australasia in Perth, Western Australia, this special issue editorial addresses novel ecosystems in ecological restoration and the inherent challenges of maintaining the highest standards of environmental stewardship and biological conservation in the face of increasing urbanization, agricultural expansion, and industrialization. Echoing others, we (the Guest Editors) view novel ecosystems as offering opportunities for conservation and restoration in the coming years and a pragmatic recognition that it may not always be possible, or desirable, to overcome adverse consequences of environmental degradation to reinstate historical systems. Being mindful of hubris and taking into account difficulties with identification, novel ecosystems may be viewed as a temporary or interim stage on the way towards the evolution of other future ecosystems able to supply a variety of ecosystem services, while attempting to maintain and enhance biodiversity, function and resilience. Here, a concise summary of contributions to the special issue and their significance to the field of restoration ecology is provided noting that authors were tasked to answer whether novel ecosystems are innovative planning or lowering the bar in ecological restoration. Core themes shared by the manuscripts are elucidated leading to guiding principles and, more importantly, an assessment of how and why restoration priorities are changing in the 21st century.