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.

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

Ecological restoration has grown rapidly and now encompasses not only classic ecological theory but also utilitarian concerns, such as preparedness for climate change and provisioning of ecosystem services. Three dominant perspectives compete to influence the science and practice of river restoration. A strong focus on channel morphology has led to approaches that involve major Earth-moving activities, such as channel reconfiguration with the unmet assumption that ecological recovery will follow. Functional perspectives of river restoration aim to regain the full suite of biogeochemical, ecological, and hydrogeomorphic processes that make up a healthy river, and though there is well-accepted theory to support this, research on methods to implement and assess functional restoration projects is in its infancy. A plethora of new studies worldwide provide data on why and how rivers are being restored as well as the project outcomes. Measurable improvements postrestoration vary by restoration method and measur...

http://lifeserv.bgu.ac.il/wb/yziv/media/Palmer%20et%20al-2014-AnnRevEcolSyst-Ecological%20Restoration%20of%20Streams%20and%20Rivers-Shifting%20Strategies%20and%20Shifting%20Goals.pdf

Ecological Restoration of Streams and Rivers: Shifting Strategies and Shifting Goals

Arctic precipitation is projected to increase and this study shows that rainfall will become the dominant phase of precipitation, with a decrease in snowfall across all seasons. Climate models project a strong increase in Arctic precipitation over the coming century1, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat2. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow3. However, little is known about future changes in the distributions of rainfall and snowfall in the Arctic. Here we use 37 state-of-the-art climate models in standardized twenty-first-century (2006–2100) simulations4 to show a decrease in average annual Arctic snowfall (70°–90° N), despite the strong precipitation increase. Rain is projected to become the dominant form of precipitation in the Arctic region (2091–2100), as atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rainfall and snowfall will heavily impact Arctic hydrology (for example, river discharge, permafrost melt)5,6,7, climatology (for example, snow, sea-ice albedo and melt)8,9 and ecology (for example, water and food availability)5,10.

Towards a rain-dominated Arctic

The global restoration movement is gaining momentum. International and national leaders are demonstrating unparalleled political will for achieving ambitious targets. However, the knowledge base for implementing large-scale forest and landscape restoration (FLR) needs further development. Besides application of scientific and local knowledge, a broad understanding of the social, economic, and environmental context in which this knowledge is being applied is also needed. To address knowledge gaps and guide implementation of FLR at local to global scales we propose a knowledge creation agenda that we derive from emerging policy goals. We present a holistic approach that addresses food security, ecosystem services, and livelihoods, and that supports implementation by a wide array of actors from farmers and municipalities to corporations and state agencies. Our knowledge creation agenda is based on six broad policy goals, with several associated knowledge gaps for each goal. We recognize that this agenda is simply a starting point and will surely evolve and become more locally focused as the concept of FLR gains ground and as multiple groups of stakeholders engage in the long-term process of restoring functionality and value to ecosystems and landscapes around the world.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/conl.12220

A Policy-Driven Knowledge Agenda for Global Forest and Landscape Restoration

http://bioscience.oxfordjournals.org XXXX XXXX / Vol. XX No. X BioScience 1 BioScience XX: 1–12. Published by Oxford University Press on behalf of the American Institute of Biological Sciences 2014. This work is written by US Government employees and is in the public domain in the US. doi:10.1093/biosci/biu036 Advance Access publication XXXX XX, XXXX Using Beaver Dams to Restore Incised Stream Ecosystems

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Using Beaver Dams to Restore Incised Stream Ecosystems

Published research emphasizes rapid downstream export of terrestrial carbon from mountainous headwater rivers, but little work focuses on mechanisms that create carbon storage along these rivers, or on the volume of carbon storage. Here we estimate organic carbon stored in diverse valley types of headwater rivers in Rocky Mountain National Park, CO, USA. We show that low-gradient, broad valley bottoms with old-growth forest or active beaver colonies store the great majority of above- and below-ground carbon. These laterally unconfined valley segments constitute o25% of total river length, but store B75% of the carbon. Floodplain sediment and coarse wood dominate carbon storage. Our estimates of riverine carbon storage represent a previously undocumented but important carbon sink. Our results indicate that: not all mountainous rivers rapidly export carbon; not all valley segments are equally important in carbon storage; and historical changes in riverine complexity have likely reduced carbon storage.

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Mechanisms of carbon storage in mountainous headwater rivers

We evaluate the validity of the beaver-meadow complex hypothesis, used to explain the deposition of extensive fine sediment in broad, low-gradient valleys. Previous work establishes that beaver damming forms wet meadows with multi-thread channels and enhanced sediment storage, but the long-term geomorphic effects of beaver are unclear. We focus on two low-gradient broad valleys, Beaver Meadows and Moraine Park, in Rocky Mountain National Park (Colorado, USA). Both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes. We examine the geomorphic significance of beaver-pond sediment by determining the rates and types of sedimentation since the middle Holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition. Sediment analyses from cores and cutbanks indicate that 33–50% of the alluvial sediment in Beaver Meadows is ponded and 28–40% was deposited in-channel; in Moraine Park 32–41% is ponded sediment and 40–52% was deposited in-channel. Radiocarbon ages spanning 4300 years indicate long-term aggradation rates of ~0.05 cm yr-1. The observed highly variable short-term rates indicate temporal heterogeneity in aggradation, which in turn reflects spatial heterogeneity in processes at any point in time. Channel complexity increases directly downstream of beaver dams. The increased complexity forms a positive feedback for beaver-induced sedimentation; the multi-thread channel increases potential channel length for further damming, which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped. Channel complexity decreased significantly as surveyed beaver population decreased. Beaver Meadows and Moraine Park represent settings where beaver substantially influence post-glacial floodplain aggradation. These findings underscore the importance of understanding the historical range of variability of valley bottom processes, and implications for environmental restoration. Copyright © 2011 John Wiley & Sons, Ltd.

The beaver meadow complex revisited – the role of beavers in post-glacial floodplain development

We reviewed follow-up studies from Finnish and Swedish streams that have been restored after timber floating to assess the abiotic and biotic responses to restoration. More specifically, from a review of 18 case studies (16 published and 2 unpublished), we determined whether different taxonomic groups react differently or require different periods of time to respond to the same type of restoration. Restoration entailed returning coarse sediment (cobbles and boulders) and sometimes large wood to previously channelized turbulent reaches, primarily with the objective of meeting habitat requirements of naturally reproducing salmonid fish. The restored streams showed a consistent increase in channel complexity and retention capacity, but the biotic responses were weak or absent in most species groups. Aquatic mosses growing on boulders were drastically reduced shortly after restoration, but in most studies, they recovered after a few years. Riparian plants, macroinvertebrates and fish did not show any consistent trends in response. We discuss seven alternative explanations to these inconsistent results and conclude that two decades is probably too short a time for most organisms to recover. We recommend long-term monitoring using standardized methods, a landscape-scale perspective and a wider range of organisms to improve the basis for judging to what extent restoration in boreal streams has achieved its goal of reducing the impacts from timber floating.

Riparian and in‐stream restoration of boreal streams and rivers: success or failure?

Traditionally, stream channel planform has been viewed as a function of larger watershed and valley-scale physical variables, including valley slope, the amount of discharge, and sediment size and load. Biotic processes serve a crucial role in transforming channel planform among straight, braided, meandering, and anabranching styles by increasing stream-bank stability and the probability of avulsions, creating stable multithread (anabranching) channels, and affecting sedimentation dynamics. We review the role of riparian vegetation and channel-spanning obstructions—beaver dams and logjams—in altering channel–floodplain dynamics in the southern Rocky Mountains, and we present channel planform scenarios for combinations of vegetation and beaver populations or old-growth forest that control logjam formation. These conceptual models provide understanding of historical planform variability throughout the Holocene and outline the implications for stream restoration or management in broad, low-gradient headwater valleys, which are important for storing sediment, carbon, and nutrients and for supporting a diverse riparian community.

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Biotic Drivers of Stream Planform Implications for Understanding the Past and Restoring the Future

The important role of vegetation in adding cohesion and stabilizing streambanks has been widely recognized in several aspects of fluvial geomorphology, including stream restoration and studies of long-term channel change. Changes in planform between braided, meandering, and anabranching forms have been attributed to the impacts of vegetation on hydraulic roughness and bank stability. However, these studies focus either on flume studies where analog vegetation is used, or case studies featuring one species, which is commonly invasive. We present functional differences of bank-stabilizing root characteristics and added cohesion, with vegetation categorized as woody and non-woody and by the vegetation groups of trees, shrubs, graminoids, and forbs. We analyzed root morphology and tensile strength of 14 species common to riparian areas in the southern Rocky Mountains, in field sites along streambanks in the montane and subalpine zones of the Colorado Front Range. Using the vegetation root component (RipRoot) of a physically-based bank stability model (BSTEM), we estimated the added cohesion for various sediment textures with the addition of each of the 14 species. Significant differences exist between woody and non-woody vegetation and between the four vegetation categories with respect to the coefficient of the root tensile strength curve, lateral root extent, and maximum root diameter. Woody vegetation (trees and shrubs) have higher values of all three parameters than non-woody species. Tree roots add significantly more cohesion to streambanks than forb roots. Additionally, rhizomes may play an important role in determining the reach-scale effects of roots on bank stabilization. Differences in root characteristics and added cohesion among vegetation categories have several important implications, including determining the likelihood of planform change, developing guidelines for the use of bank-stabilizing vegetation, and linking the effect of vegetation to geomorphic structure that can benefit ecosystem functioning. Copyright © 2014 John Wiley & Sons, Ltd.

Lina E. Polvi

Papers

Mechanisms of carbon storage in mountainous headwater rivers

The beaver meadow complex revisited – the role of beavers in post-glacial floodplain development

Riparian and in‐stream restoration of boreal streams and rivers: success or failure?

Biotic Drivers of Stream Planform Implications for Understanding the Past and Restoring the Future

Modeling the functional influence of vegetation type on streambank cohesion