Prescribed fire in North American forests and woodlands: History, current practice, and challenges

Ryan, K.C., E.E. Knapp, and J.M. Varner, 2013: “Prescribed fire in North American forests and woodlands: History, current practice, and challenges.” Frontiers in Ecology and the Environment, v. 11, pp. e15–e24, doi: 10.1890/120329.

Whether ignited by lightning or by Native Americans, fire once shaped many North American ecosystems. Euro–American settlement and 20th-century fire suppression practices drastically altered historic fire regimes, leading to excessive fuel accumulation and uncharacteristically severe wildfires in some areas and diminished flammability resulting from shifts to more fire-sensitive forest species in others. Prescribed fire is a valuable tool for fuel management and ecosystem restoration, but the practice is fraught with controversy and uncertainty. Here, we summarize fire use in the forests and woodlands of North America and the current state of the practice, and explore challenges associated with the use of prescribed fire. Although new scientific knowledge has reduced barriers to prescribed burning, societal aversion to risk often trumps known, long-term ecological benefits. Broader implementation of prescribed burning and strategic management of wildfires in fire-dependent ecosystems will require improved integration of science, policy, and management, and greater societal acceptance through education and public involvement in land-management issues.

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Keeping wetlands wet in the western United States: Adaptations to drought in agriculture-dominated human-natural systems

Downard, R., and J. Endter-Wada, 2013: “Keeping wetlands wet in the western United States: Adaptations to drought in agriculture-dominated human-natural systems.” Journal of Environmental Management, v. 131, pp. 394-406, doi: 10.1016/j.jenvman.2013.10.008.

Water is critical to protecting wetlands in arid regions, especially in agriculture-dominated watersheds. This comparative case study analyzes three federal wildlife refuges in the Bear River Basin of the U.S. West where refuge managers secured water supplies by adapting to their local environmental context and their refuge’s relationship to agriculture in being either irrigation-dependent, reservoir-adjacent or diked-delta wetlands. We found that each refuge’s position confers different opportunities for securing a water supply and entails unique management challenges linked to agricultural water uses. Acquiring contextually-appropriate water rights portfolios was important for protecting these arid region wetlands and was accomplished through various strategies. Once acquired, water is managed to buffer wetlands against fluctuations caused by a dynamic climate and agricultural demands, especially during droughts. Management plans are responsive to needs of neighboring water users and values of the public at large. Such context-specific adaptations will be critical as the West faces climate change and population growth that threaten wetlands and agricultural systems to which they are linked.

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Human health impacts of ecosystem alteration

Myers, S.S., L. Gaffikin, C.D. Golden, R.S. Ostfeld, K.H. Redford, T.H. Ricketts, W.R. Turner, and S.A. Osofsky, 2013: “Human health impacts of ecosystem alteration.” Proceedings of the National Academy of Sciences, v. 110, pp. 18,753-18,760, doi: 10.1073/pnas.1218656110.

Human activity is rapidly transforming most of Earth’s natural systems. How this transformation is impacting human health, whose health is at greatest risk, and the magnitude of the associated disease burden are relatively new subjects within the field of environmental health. We discuss what is known about the human health implications of changes in the structure and function of natural systems and propose that these changes are affecting human health in a variety of important ways. We identify several gaps and limitations in the research that has been done to date and propose a more systematic and comprehensive approach to applied research in this field. Such efforts could lead to a more robust understanding of the human health impacts of accelerating environmental change and inform decision making in the land-use planning, environmental conservation, and public health policy realms.

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Food-web dynamics in a large river discontinuum

Cross, W.F., C.V. Baxter, E.J. Rosi-Marshall, R.O. Hall, Jr., T.A. Kennedy, K.C. Donner, H.A. Wellard Kelly, S.E.Z. Seegert, K.E. Behn, and M.D. Yard, 2013: “Food-web dynamics in a large river discontinuum.” Ecological Monographs, v. 83, pp. 311-337, doi: 10.1890/12-1727.1.

Nearly all ecosystems have been altered by human activities, and most communities are now composed of interacting species that have not co-evolved. These changes may modify species interactions, energy and material flows, and food-web stability. Although structural changes to ecosystems have been widely reported, few studies have linked such changes to dynamic food-web attributes and patterns of energy flow. Moreover, there have been few tests of food-web stability theory in highly disturbed and intensely managed freshwater ecosystems. Such synthetic approaches are needed for predicting the future trajectory of ecosystems, including how they may respond to natural or anthropogenic perturbations.

We constructed flow food webs at six locations along a 386-km segment of the Colorado River in Grand Canyon (Arizona, USA) for three years. We characterized food-web structure and production, trophic basis of production, energy efficiencies, and interaction-strength distributions across a spatial gradient of perturbation (i.e., distance from Glen Canyon Dam), as well as before and after an experimental flood. We found strong longitudinal patterns in food-web characteristics that strongly correlated with the spatial position of large tributaries. Above tributaries, food webs were dominated by nonnative New Zealand mudsnails (62% of production) and nonnative rainbow trout (100% of fish production). The simple structure of these food webs led to few dominant energy pathways (diatoms to few invertebrate taxa to rainbow trout), large energy inefficiencies (i.e., <20% of invertebrate production consumed by fishes), and right-skewed interaction-strength distributions, consistent with theoretical instability.

Below large tributaries, invertebrate production declined 18-fold, while fish production remained similar to upstream sites and comprised predominately native taxa (80–100% of production). Sites below large tributaries had increasingly reticulate and detritus-based food webs with a higher prevalence of omnivory, as well as interaction strength distributions more typical of theoretically stable food webs (i.e., nearly twofold higher proportion of weak interactions). Consistent with theory, downstream food webs were less responsive to the experimental flood than sites closest to the dam. We show how human-induced shifts to food-web structure can affect energy flow and interaction strengths, and we show that these changes have consequences for food-web function and response to perturbations.

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Linking land use, in-stream stressors, and biological condition to infer causes of regional ecological impairment in streams

Vander Laan, J.J., C.P. Hawkins, J.R. Olson, and R.A. Hill, 2013: “Linking land use, in-stream stressors, and biological condition to infer causes of regional ecological impairment in streams.” Freshwater Science, v. 32, pp. 801-820, doi: 10.1899/12-186.1.

We used field-derived data from streams in Nevada, USA, to quantify relationships between stream biological condition, in-stream stressors, and potential sources of stress (land use). We used 2 freshwater macroinvertebrate-based indices to measure biological condition: a multimetric index (MMI) and an observed to expected (O/E) index of taxonomic completeness. We considered 4 categories of potential stressors: dissolved metals, total dissolved solids, nutrients, and flow alteration. For physicochemical factors that varied predictably across natural environmental gradients, we quantified potential stress as the site-specific difference between observed (O) and expected (E) levels of each factor (O–Estress). We then used 2 sets of Random Forest models to quantify relationships between: 1) biological condition and potential stressors, and 2) stressor values and land uses. The 2 indices of biological condition were differentially responsive to stressors, indicating that no single measure of biological condition could fully characterize assemblage response to stress. Total dissolved solids (as measured by electrical conductivity [EC]) and metal contamination were the stressors most strongly associated with biological degradation. The most likely sources of these stressors were agriculture, urban development, and mining. Our findings highlight the need to develop EC criteria for streams. Measures of biological condition and stress that account for natural variability should reduce errors of inference and increase confidence in causal analyses. This approach will require development of robust models capable of predicting physical and chemical reference conditions. Causal analyses for individual sites require appropriate hypotheses about which stressors and what levels of stress can cause biological degradation. Our study demonstrates the usefulness of field data collected from multiple sites within a region for developing these hypotheses.

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Geomorphology and ecology: Unifying themes for complex systems in biogeomorphology

Stallins, J.A., 2006: “Geomorphology and ecology: Unifying themes for complex systems in biogeomorphology.” Geomorphology, v. 77, pp. 207-216, doi: 10.1016/j.geomorph.2006.01.005.

The interaction of geomorphic and ecologic landscape components has been largely conceptualized as independent. In one direction, geomorphic processes and landforms shape the distribution of biota. Conversely, in the other direction, biota modify geomorphic processes and landforms. Increasingly, the interactions between geomorphic and ecological components are more circular and developmentally intertwined. In this paper, I integrate these two independent perspectives within the framework of complexity theory. I outline four themes that characterize complex systems in biogeomorphology: multiple causality and the concept of recursivity, the influence of organisms that function as ecosystem engineers, the expression of an ecological topology, and ecological memory. Implicit in all of these themes is the recognition that biogeomorphic systems are open and path dependent. They may exhibit a range of assembly states, from self-reinforcing stability domains to more transient configurations of organisms and environment.

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The negative relief of large river floodplains

Lewin, J., and P.J. Ashworth, 2013: “The negative relief of large river floodplains.” Earth-Science Reviews, doi: 10.1016/j.earscirev.2013.10.014.

Large floodplains have multiple and complex negative relief assemblages in which depressions fall below local or general floodplain surfaces at a variety of scales. The generation and dynamics of negative relief along major alluvial corridors are described and compared. Such depressions are significant for the storage and passage of surface waters, the creation of a range of riparian, wetland, lacustrine and flowing-water habitats, and the long-term accumulation of organic materials.

Working on trunk channel remnants, drowned valleys and subsidence basins, fluvial processes modify floodplain negative relief through differential erosion and sedimentation. Effectively this takes place in three genetic zones: rheic, transitional and perirheic. We show that transitional zones marginal to active channels significantly diversify form complexes, and we demonstrate the diachronous nature of zonal processes and the complex nature and pace of depression modification and infilling. Four less well-understood sets of coupled phenomena are assessed: (i) floodplains associated with discontinuous river banks, (ii) the scales and types of scroll bar generation, (iii) factors underlying the contrasts between meander and braidplain surface relief, and (iv) the generation and function of large floodplain wetlands and lakes.

The survival likelihood of surface negative relief relates to geomorphological connectivity; this is described for each of the rheic, transitional and perirheic zones. Implications for contemporary aquatic system management are discussed. A key to understanding and managing negative relief on large river floodplains, and their associated ecologies and sedimentation, is to quantify both sedimentological and hydrological river-floodplain connectivity.

Open Access

Ecologically relevant geomorphic attributes of streams are impaired by even low levels of watershed effective imperviousness

Vietz, G.J., M.J. Sammonds, C.J. Walsh, T.D. Fletcher, I.D. Rutherfurd, and M.J. Stewardson, 2013: “Ecologically relevant geomorphic attributes of streams are impaired by even low levels of watershed effective imperviousness.” Geomorphology, doi: 10.1016/j.geomorph.2013.09.019.

Urbanization almost inevitably results in changes to stream morphology. Understanding the mechanisms for such impacts is a prerequisite to minimizing stream degradation and achieving restoration goals. However, investigations of urban-induced changes to stream morphology typically use indicators of watershed urbanization that may not adequately represent degrading mechanisms and that commonly focus on geomorphic attributes such as channel dimensions that may be of little significance to the ecological goals for restoration. We address these shortcomings by testing if a measure characterizing urban stormwater drainage system connections to streams (effective imperviousness, EI) is a better predictor of change to ecologically relevant geomorphic attributes than a more general measure of urban density (total imperviousness, TI). We test this for 17 sites in independent watersheds across a gradient of urbanization. We found that EI was a better predictor of all geomorphic variables tested than was TI. Bank instability was positively correlated with EI, while width/depth (a measure of channel incision), bedload sediment depth, and frequency of bars, benches, and large wood were negatively correlated. Large changes in all geomorphic variables were detected at very low levels of EI (< 2–3%). Excess urban stormwater runoff, as represented by EI, drives geomorphic change in urban streams, highlighting the dominant role of the stormwater drainage system in efficiently transferring stormwater runoff from impervious surfaces to the stream, as found for ecological indicators. It is likely that geomorphic condition of streams in urbanizing watersheds, particularly those attributes of ecological relevance, can only be maintained if excess urban stormwater flows are kept out of streams through retention and harvesting. The extent to which EI can be reduced within urban and urbanizing watersheds, through techniques such as distributed stormwater harvesting and infiltration, and the components of the hydrologic regime to be addressed, require further investigation.

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Modeling the interactions between river morphodynamics and riparian vegetation

Camporeale, C., E. Perucca, L. Ridolfi, and A.M. Gurnell, 2013: “Modeling the interactions between river morphodynamics and riparian vegetation.” Reviews of Geophysics, v. 51, pp. 379-414, doi: 10.1002/rog.20014.

The study of river-riparian vegetation interactions is an important and intriguing research field in geophysics. Vegetation is an active element of the ecological dynamics of a floodplain which interacts with the fluvial processes and affects the flow field, sediment transport, and the morphology of the river. In turn, the river provides water, sediments, nutrients, and seeds to the nearby riparian vegetation, depending on the hydrological, hydraulic, and geomorphological characteristic of the stream. In the past, the study of this complex theme was approached in two different ways. On the one hand, the subject was faced from a mainly qualitative point of view by ecologists and biogeographers. Riparian vegetation dynamics and its spatial patterns have been described and demonstrated in detail, and the key role of several fluvial processes has been shown, but no mathematical models have been proposed. On the other hand, the quantitative approach to fluvial processes, which is typical of engineers, has led to the development of several morphodynamic models. However, the biological aspect has usually been neglected, and vegetation has only been considered as a static element. In recent years, different scientific communities (ranging from ecologists to biogeographers and from geomorphologists to hydrologists and fluvial engineers) have begun to collaborate and have proposed both semiquantitative and quantitative models of river-vegetation interconnections. These models demonstrate the importance of linking fluvial morphodynamics and riparian vegetation dynamics to understand the key processes that regulate a riparian environment in order to foresee the impact of anthropogenic actions and to carefully manage and rehabilitate riparian areas. In the first part of this work, we review the main interactions between rivers and riparian vegetation, and their possible modeling. In the second part, we discuss the semiquantitative and quantitative models which have been proposed to date, considering both multi- and single-thread rivers.

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Climate change, ecosystem services, and costs of action and inaction: Scoping the interface

Rodríguez-Labajos, B., 2013: “Climate change, ecosystem services, and costs of action and inaction: Scoping the interface.” WIREs Clim Change, doi: 10.1002/wcc.247.

Cost calculations related to climate change have accrued much intellectual effort. However, few works approach the assessment from the point of view of the effects of climate variability and change in ecosystem service provision. Failure to act plausibly leads to ecological, social, and economic damages as a result of ecosystem change. The necessary actions to cope with unavoidable damages from such change generate adaptation costs, while mitigation costs are associated with actions to tackle undesired future changes in the ecosystems. Examples of these effects and related costs, based on representative studies, are reviewed following the organizing scheme of the ecosystem services approach. The examination of case examples reveals the potential and limits of monetary versus non-monetary estimations of impacts in human wellbeing from climate change-related changes in the ecosystems, trade-offs between types of ecosystem service provision and implications of timing in action. This article further discusses the necessary steps to advance in an inclusive scrutiny of the costs associated with the effects of climate change on ecosystem service provision.

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