Samantha J. Capon

Riparian Ecosystems in the 21st Century: Hotspots for Climate Change Adaptation?

Riparian ecosystems in the 21st century are likely to play a critical role in determining the vulnerability of natural and human systems to climate change, and in influencing the capacity of these systems to adapt. Some authors have suggested that riparian ecosystems are particularly vulnerable to climate change impacts due to their high levels of exposure and sensitivity to climatic stimuli, and their history of degradation. Others have highlighted the probable resilience of riparian ecosystems to climate change as a result of their evolution under high levels of climatic and environmental variability. We synthesize current knowledge of the vulnerability of riparian ecosystems to climate change by assessing the potential exposure, sensitivity, and adaptive capacity of their key components and processes, as well as ecosystem functions, goods and services, to projected global climatic changes. We review key pathways for ecological and human adaptation for the maintenance, restoration and enhancement of riparian ecosystem functions, goods and services and present emerging principles for planned adaptation. Our synthesis suggests that, in the absence of adaptation, riparian ecosystems are likely to be highly vulnerable to climate change impacts. However, given the critical role of riparian ecosystem functions in landscapes, as well as the strong links between riparian ecosystems and human well-being, considerable means, motives and opportunities for strategically planned adaptation to climate change also exist. The need for planned adaptation of and for riparian ecosystems is likely to be strengthened as the importance of many riparian ecosystem functions, goods and services will grow under a changing climate. Consequently, riparian ecosystems are likely to become adaptation ‘hotspots’ as the century unfolds.

RESTORATION OF RIVERS USED FOR TIMBER FLOATING: EFFECTS ON RIPARIAN PLANT DIVERSITY

Fluvial processes such as flooding and sediment deposition play a crucial role in structuring riparian plant communities. In rivers throughout the world, these processes have been altered by channelization and other anthropogenic stresses. Yet despite increasing awareness of the need to restore natural flow regimes for the preservation of riparian biodiversity, few studies have examined the effects of river restoration on riparian ecosystems. In this study, we examined the effects of restoration in the Ume River system, northern Sweden, where tributaries were channelized to facilitate timber floating in the 19th and early 20th centuries. Restoration at these sites involved the use of heavy machinery to replace instream boulders and remove floatway structures that had previously lined stream banks and cut off secondary channels. We compared riparian plant communities along channelized stream reaches with those along reaches that had been restored 3-10 years prior to observation. Species richness and evenness were significantly increased at restored sites, as were floodplain inundation frequencies. These findings demonstrate how river restoration and associated changes in fluvial disturbance regimes can enhance riparian biodiversity. Given that riparian ecosystems tend to support a disproportionate share of regional species pools, these findings have potentially broad implications for biodiversity conservation at regional or landscape scales.

Spatial variability of the soil seed bank in a heterogeneous ephemeral wetland system in semi-arid Australia

Soil seed banks are an important component of plant community diversity in ephemeral wetlands, allowing many species to persist through unpredictable periods of flood and drought. Spatial variation of extant vegetation in such habitats commonly reflects patterns of flood history and often varies predictably between broadly differing hydro-geomorphic habitat types. Here we investigate whether spatial variation of soil seed banks is similarly controlled by fluvial processes at this scale. Results are presented from a seedling emergence trial using samples collected from a range of habitat types, and at different scales within these, in the ephemeral Narran Lakes system in semi-arid Australia. Composition and structure of soil seed banks varied significantly between habitat types reflecting broad differences in flood frequency. As predicted, germinable seed abundance was found to be highest in intermediately flooded habitats. Variability in soil seed bank composition at a local scale was also found to be influenced by hydrology with greater spatial heterogeneity evident in the river channel as well as amongst the least frequently inundated riparian and floodplain habitats.

Regime shifts, thresholds and multiple stable states in freshwater ecosystems; a critical appraisal of the evidence

The concepts of ecosystem regime shifts, thresholds and alternative or multiple stable states are used extensively in the ecological and environmental management literature. When applied to aquatic ecosystems, these terms are used inconsistently reflecting differing levels of supporting evidence among ecosystem types. Although many aquatic ecosystems around the world have become degraded, the magnitude and causes of changes, relative to the range of historical variability, are poorly known. A working group supported by the Australian Centre for Ecological Analysis and Synthesis (ACEAS) reviewed 135 papers on freshwater ecosystems to assess the evidence for pressure-induced non-linear changes in freshwater ecosystems; these papers used terms indicating sudden and non-linear change in their titles and key words, and so was a positively biased sample. We scrutinized papers for study context and methods, ecosystem characteristics and focus, types of pressures and ecological responses considered, and the type of change reported (i.e., gradual, non-linear, hysteretic or irreversible change). There was little empirical evidence for regime shifts and changes between multiple or alternative stable states in these studies although some shifts between turbid phytoplankton-dominated states and clear-water, macrophyte-dominated states were reported in shallow lakes in temperate climates. We found limited understanding of the subtleties of the relevant theoretical concepts and encountered few mechanistic studies that investigated or identified cause-and-effect relationships between ecological responses and nominal pressures. Our results mirror those of reviews for estuarine, nearshore and marine aquatic ecosystems, demonstrating that although the concepts of regime shifts and alternative stable states have become prominent in the scientific and management literature, their empirical underpinning is weak outside of a specific environmental setting. The application of these concepts in future research and management applications should include evidence on the mechanistic links between pressures and consequent ecological change. Explicit consideration should also be given to whether observed temporal dynamics represent variation along a continuum rather than categorically different states.

When trends intersect: The challenge of protecting freshwater ecosystems under multiple land use and hydrological intensification scenarios

Intensification of the use of natural resources is a world-wide trend driven by the increasing demand for water, food, fibre, minerals and energy. These demands are the result of a rising world population, increasing wealth and greater global focus on economic growth. Land use intensification, together with climate change, is also driving intensification of the global hydrological cycle. Both processes will have major socio-economic and ecological implications for global water availability. In this paper we focus on the implications of land use intensification for the conservation and management of freshwater ecosystems using Australia as an example. We consider this in the light of intensification of the hydrologic cycle due to climate change, and associated hydrological scenarios that include the occurrence of more intense hydrological events (extreme storms, larger floods and longer droughts). We highlight the importance of managing water quality, the value of providing environmental flows within a watershed framework and the critical role that innovative science and adaptive management must play in developing proactive and robust responses to intensification. We also suggest research priorities to support improved systemic governance, including adaptation planning and management to maximise freshwater biodiversity outcomes while supporting the socio-economic objectives driving land use intensification. Further research priorities include: i) determining the relative contributions of surface water and groundwater in supporting freshwater ecosystems; ii) identifying and protecting freshwater biodiversity hotspots and refugia; iii) improving our capacity to model hydro-ecological relationships and predict ecological outcomes from land use intensification and climate change; iv) developing an understanding of long term ecosystem behaviour; and v) exploring systemic approaches to enhancing governance systems, including planning and management systems affecting freshwater outcomes. A major policy challenge will be the integration of land and water management, which increasingly are being considered within different policy frameworks.

EFFECTS OF FLOODING ON SEEDLING EMERGENCE FROM THE SOIL SEED BANK OF A LARGE DESERT FLOODPLAIN

Australia’s large desert floodplains are among the world’s most hydrologically variable wetlands and vegetation in these habitats changes dramatically over time in response to flooding and drought. Annual forb and grass communities in these desert floodplains rely on large, diverse soil seed banks as critical sources of propagules for recruitment. I investigated the effects of flooding on seedling emergence from the soil seed bank of the Cooper Creek floodplain in arid central Australia. My objective was to determine the effects of differences in both short-term flooding characteristics as well as the longer-term flood history of sediments on the composition of plant communities establishing from the soil seed bank. I conducted a greenhouse experiment in which sediments collected from high (inundated at least once every 1–5 yrs), medium (inundated approximately once in every 5–10 yrs), and low (inundated less than once a decade) flood frequency zones were subjected to different durations of submergence, rates of drawdown (i.e., duration of post-submergence waterlogging), and seasonal timing of flooding. The abundance of emerging seedlings more than doubled in response to longer overall durations of wetting, but the relative duration of submergence (i.e., 8 vs. 4 weeks) versus subsequent soil waterlogging (i.e., 4 vs. 8 weeks) within this period did not have a significant effect. The duration of submergence versus waterlogging did however influence the composition of emerging seedlings with almost twice as many annual monocots appearing following longer durations of submergence. All dominant species emerged frequently following both summer and winter flooding, suggesting opportunistic germination strategies. The composition of moderately abundant and rare species, however, differed in response to the seasonal timing of inundation with monocots more common following summer floods and forbs following winter flooding. Common species were well-distributed in the soil seed bank across the flood history gradient, and the species richness of emerging seedlings did not vary between different flood frequency zones. However, seedlings of species emerging from low flood frequency zone samples tended to be less abundant and differed in composition compared with those emerging from samples of high and medium flood frequency zones. My results suggest that changes to both short- and long-term flooding patterns, through flow management or climate change, are likely to affect vegetation responses to inundation in these desert floodplains. Reductions in flood pulse magnitude and frequency, for instance, could result in a decline in the abundance of valuable pasture grasses germinating in response to summer flooding and a loss of hydrophytic species in rarely flooded areas.

Applications of Bayesian belief networks in water resource management

Bayesian belief networks (BBNs) are probabilistic graphical models that can capture and integrate both quantitative and qualitative data, thus accommodating data-limited conditions. This paper systematically reviews applications of BBNs with respect to spatial factors, water domains, and the consideration of climate change impacts. The methods used for constructing and validating BBN models, and their applications in different forms of decision-making support are examined. Most reviewed publications originate from developed countries (70%), in temperate climate zones (42%), and focus mainly on water quality (42%). In 60% of the reviewed applications model validation was based on the expert or stakeholder evaluation and sensitivity analysis, and whilst in 27% model performance was not discussed. Most reviewed articles applied BBNs in strategic decision-making contexts (52%). Integrated modelling tools for addressing challenges of dynamically complex systems were also reviewed by analysing the strengths and weaknesses of BBNs, and integration of BBNs with other modelling tools. The application of BBNs to water resource management was rarely applied in developing countries and in tropical regions.Only 8% reviewed papers explored potential impacts of climate change on water resources.Only 11% and 6% of reviewed articles applied influence diagrams and Object-Oriented Bayesian Networks respectively.Most reviewed articles applied BBNs in strategic decision-making contexts (52%) for water resource management.Results from BBN models were rarely compared or tested against other modelling approaches to validate their performance.

Transdisciplinary synthesis for ecosystem science, policy and management: The Australian experience

Mitigating the environmental effects of global population growth, climatic change and increasing socio-ecological complexity is a daunting challenge. To tackle this requires synthesis: the integration of disparate information to generate novel insights from heterogeneous, complex situations where there are diverse perspectives. Since 1995, a structured approach to inter-, multi- and trans-disciplinary(1) collaboration around big science questions has been supported through synthesis centres around the world. These centres are finding an expanding role due to ever-accumulating data and the need for more and better opportunities to develop transdisciplinary and holistic approaches to solve real-world problems. The Australian Centre for Ecological Analysis and Synthesis (ACEAS ) has been the pioneering ecosystem science synthesis centre in the Southern Hemisphere. Such centres provide analysis and synthesis opportunities for time-pressed scientists, policy-makers and managers. They provide the scientific and organisational environs for virtual and face-to-face engagement, impetus for integration, data and methodological support, and innovative ways to deliver synthesis products. We detail the contribution, role and value of synthesis using ACEAS to exemplify the capacity for synthesis centres to facilitate trans-organisational, transdisciplinary synthesis. We compare ACEAS to other international synthesis centres, and describe how it facilitated project teams and its objective of linking natural resource science to policy to management. Scientists and managers were brought together to actively collaborate in multi-institutional, cross-sectoral and transdisciplinary research on contemporary ecological problems. The teams analysed, integrated and synthesised existing data to co-develop solution-oriented publications and management recommendations that might otherwise not have been produced. We identify key outcomes of some ACEAS working groups which used synthesis to tackle important ecosystem challenges. We also examine the barriers and enablers to synthesis, so that risks can be minimised and successful outcomes maximised. We argue that synthesis centres have a crucial role in developing, communicating and using synthetic transdisciplinary research.

Policy considerations for managing wetlands under a changing climate

Drawing on the experience and lessons of wetland researchers and managers in Australia and New Zealand, we examined the implications of climate change for wetland policy and management, and identified potential adaptation responses and the information needed to support these. First, we considered wetland vulnerability to climate change, focusing on wetland exposure and sensitivity. We then outlined the existing policy context for dealing with climate change, with an emphasis on the Ramsar Convention on Wetlands. We then considered how the objectives and targets for wetland management can be set in the face of climate change, how management can be adapted to climate change given the uncertainties involved, and how we can monitor and evaluate wetland condition in the face of climate change. We concluded with a set of principles to guide adaptation of wetland conservation and management policy to climate change.

An Impossible Prescription: Why Science Cannot Determine Environmental Water Requirements for a Healthy Murray-Darling Basin

The concept of environmental water requirements (EWRs) is central to Australia’s present approach to water reform. Current decision-making regarding environmental water relies strongly on the notion that EWRs necessary to meet targets associated with ecological objectives for asset sites can be scientifically defined, thus enabling the ecological outcomes of alternative water management scenarios to be evaluated in a relatively straightforward fashion in relation to these flow thresholds or targets. We argue, however, that the ecological objectives and targets currently underpinning the development of EWRs in the Murray-Darling Basin are insufficient to permit the identification of exact water requirements or flow thresholds. Because of the dynamic and heterogeneous nature of the Murray-Darling Basin and the myriad ways in which it is valued by people, we also assert that it is unlikely that adequate ecological objectives and targets from which to determine EWRs could ever be formulated. We suggest that the current emphasis on the concept of EWRs in environmental water planning conflates science and values, perpetuating a “how much is enough?” myth whereby the significance of the social, cultural and political dimension in environmental decision-making is diminished. We support an alternative paradigm in which the contribution of ecological science to water policy and management decisions focuses on understanding ecological responses of water-dependent ecosystems and their biota to alternative management scenarios and linking these responses to the ecosystem services and human values which they support.