Rebecca E. Lester

Scientific Foundations for an IUCN Red List of Ecosystems

An understanding of risks to biodiversity is needed for planning action to slow current rates of decline and secure ecosystem services for future human use. Although the IUCN Red List criteria provide an effective assessment protocol for species, a standard global assessment of risks to higher levels of biodiversity is currently limited. In 2008, IUCN initiated development of risk assessment criteria to support a global Red List of ecosystems. We present a new conceptual model for ecosystem risk assessment founded on a synthesis of relevant ecological theories. To support the model, we review key elements of ecosystem definition and introduce the concept of ecosystem collapse, an analogue of species extinction. The model identifies four distributional and functional symptoms of ecosystem risk as a basis for assessment criteria: A) rates of decline in ecosystem distribution; B) restricted distributions with continuing declines or threats; C) rates of environmental (abiotic) degradation; and D) rates of disruption to biotic processes. A fifth criterion, E) quantitative estimates of the risk of ecosystem collapse, enables integrated assessment of multiple processes and provides a conceptual anchor for the other criteria. We present the theoretical rationale for the construction and interpretation of each criterion. The assessment protocol and threat categories mirror those of the IUCN Red List of species. A trial of the protocol on terrestrial, subterranean, freshwater and marine ecosystems from around the world shows that its concepts are workable and its outcomes are robust, that required data are available, and that results are consistent with assessments carried out by local experts and authorities. The new protocol provides a consistent, practical and theoretically grounded framework for establishing a systematic Red List of the world’s ecosystems. This will complement the Red List of species and strengthen global capacity to report on and monitor the status of biodiversity

A Ramsar wetland in crisis – the Coorong, Lower Lakes and Murray Mouth, Australia

The state of global freshwater ecosystems is increasingly parlous with water resource development degrading high-conservation wetlands. Rehabilitation is challenging because necessary increases in environmental flows have concomitant social impacts, complicated because many rivers flow between jurisdictions or countries. Australia’s Murray–Darling Basin is a large river basin with such problems encapsulated in the crisis of its Ramsar-listed terminal wetland, the Coorong, Lower Lakes and Murray Mouth. Prolonged drought and upstream diversion of water dropped water levels in the Lakes below sea level (2009–2010), exposing hazardous acid sulfate soils. Salinities increased dramatically (e.g. South Lagoon of Coorong >200 g L–1, cf. modelled natural 80 g L–1), reducing populations of waterbirds, fish, macroinvertebrates and littoral plants. Calcareous masses of estuarine tubeworms (Ficopomatus enigmaticus) killed freshwater turtles (Chelidae) and other fauna. Management primarily focussed on treating symptoms (e.g. acidification), rather than reduced flows, at considerable expense (>AU

Rehabilitating Agricultural Streams in Australia with Wood: A Review

2 billion). We modelled a scenario that increased annual flows during low-flow periods from current levels up to one-third of what the natural flow would have been, potentially delivering substantial environmental benefits and avoiding future crises. Realisation of this outcome depends on increasing environmental flows and implementing sophisticated river management during dry periods, both highly contentious options.

Does adding wood to agricultural streams enhance biodiversity? An experimental approach

Worldwide, the ecological condition of streams and rivers has been impaired by agricultural practices such as broadscale modification of catchments, high nutrient and sediment inputs, loss of riparian vegetation, and altered hydrology. Typical responses include channel incision, excessive sedimentation, declining water quality, and loss of in-stream habitat complexity and biodiversity. We review these impacts, focusing on the potential benefits and limitations of wood reintroduction as a transitional rehabilitation technique in these agricultural landscapes using Australian examples. In streams, wood plays key roles in shaping velocity and sedimentation profiles, forming pools, and strengthening banks. In the simplified channels typical of many agricultural streams, wood provides habitat for fauna, substrate for biofilms, and refuge from predators and flow extremes, and enhances in-stream diversity of fish and macroinvertebrates.Most previous restoration studies involving wood reintroduction have been in forested landscapes, but some results might be extrapolated to agricultural streams. In these studies, wood enhanced diversity of fish and macroinvertebrates, increased storage of organic material and sediment, and improved bed and bank stability. Failure to meet restoration objectives appeared most likely where channel incision was severe and in highly degraded environments. Methods for wood reintroduction have logistical advantages over many other restoration techniques, being relatively low cost and low maintenance. Wood reintroduction is a viable transitional restoration technique for agricultural landscapes likely to rapidly improve stream condition if sources of colonists are viable and water quality is suitable.

Linking water-resource models to ecosystem-response models to guide water-resource planning -- an example from the Murray--Darling Basin, Australia

Riparian clearing and the removal of wood from channels have affected many streams in agricultural landscapes. As a result, these streams often have depauperate in-stream wood loads, and therefore decreased habitat complexity and lower levels of in-stream biodiversity. The introduction of wood was investigated as a possible rehabilitation technique for agricultural streams. Wood was re-introduced to eight streams in two separate high-rainfall, intensively grazed regions of Victoria, Australia and the effect on aquatic macroinvertebrate communities was measured. The addition of wood increased overall family richness and the richness of most functional feeding groups occupying edge and benthic habitats within the stream. Wood addition led to less overlap between benthic and edge macroinvertebrate communities, suggesting increased habitat heterogeneity within the stream ecosystem. Of all sampled habitats, wood supported the greatest density of families and was colonised by all functional feeding groups. Wood habitats also had the highest overall richness and supported the most taxa that were sensitive to disturbance. These findings suggest that re-introducing wood to agricultural streams is an appropriate rehabilitation technique where those streams are affected by reduced habitat complexity. Additional work is needed to confirm these findings over larger spatial and temporal scales.

Ecohydrological and socioeconomic integration for the operational management of environmental flows

Objectively assessing ecological benefits of competing watering strategies is difficult. We present a framework of coupled models to compare scenarios, using the Coorong, the estuary for the Murray–Darling River system in South Australia, as a case study. The framework links outputs from recent modelling of the effects of climate change on water availability across the Murray–Darling Basin to a hydrodynamic model for the Coorong, and then an ecosystem-response model. The approach has significant advantages, including the following: (1) evaluating management actions is straightforward because of relatively tight coupling between impacts on hydrology and ecology; (2) scenarios of 111 years reveal the impacts of realistic climatic and flow variability on Coorong ecology; and (3) ecological impact is represented in the model by a series of ecosystem states, integrating across many organisms, not just iconic species. We applied the approach to four flow scenarios, comparing conditions without development, current water-use levels, and two predicted future climate scenarios. Simulation produced a range of hydrodynamic conditions and consequent distributions of ecosystem states, allowing managers to compare scenarios. This approach could be used with many climates and/or management actions for optimisation of flow delivery to environmental assets.

Large versus small wood in streams: the effect of wood dimension on macroinvertebrate communities

Investment in and operation of flow control infrastructure such as dams, weirs, and regulators can help increase both the health of regulated river ecosystems and the social values derived from them. This requires high-quality and high-resolution spatiotemporal ecohydrological and socioeconomic information. We developed such an information base for integrated environmental flow management in the River Murray in South Australia (SA). A hydrological model was used to identify spatiotemporal inundation dynamics. River ecosystems were classified and mapped as ecohydrological units. Ecological response models were developed to link three aspects of environmental flows (flood duration, timing, and inter-flood period) to the health responses of 16 ecological components at various life stages. Potential infrastructure investments (flow control regulators and irrigation pump relocation) were located by interpreting LiDAR elevation data, digital orthophotography, and wetland mapping information; and infrastructure costs were quantified using engineering cost models. Social values were quantified at a coarse scale as total economic value based on a national survey of willingness-to-pay for four key ecological assets; and at a local scale using mapped ecosystem service values. This information was integrated using a constrained, nonlinear, mixed-integer, compromise programming optimization model and solved using a stochastic Tabu search algorithm. We tested the model uncertainty and sensitivity using 390 Monte Carlo model runs at varying weights of ecological health vs. social values. Integrating ecohydrological and socioeconomic information identified environmental flow management regimes that efficiently achieved both ecological and social objectives. Using an ecologically weighted efficient and socially weighted efficient scenario, we illustrated model outputs including a suite of cost-effective infrastructure investments and an operational plan for new and existing flow control structures including dam releases, weir height manipulation, and regulator operation on a monthly time step. Both the investments and management regimes differed substantially between the two scenarios, suggesting that the choice of weightings on ecological and social objectives is important. This demonstrates the benefit of integrating high-quality and high-resolution spatiotemporal ecohydrological and socioeconomic information for guiding the investment in and operational management of environmental flows.

Hydrologic Landscape Regionalisation Using Deductive Classification and Random Forests

Conventionally, most research and restoration involving in-stream wood focuses on large wood (> 0.1 m diameter), excluding any smaller pieces. However, this may neglect a major component of in-stream habitat, as small wood can constitute the majority of pieces, particularly in small streams. The ecological benefi t of large wood is well established, but corresponding benefi ts associated with small wood (0.05-0.1 m diameter) have not been demonstrated. To test the effect of wood dimension on macroinvertebrate community composition, we compared the fauna occupying large wood habitats with that occupying small wood at eight streams in south-eastern Australia. The relationships between wood dimensions and its macroinvertebrate fauna were complex. Community composi- tion did not vary with wood dimension, and no signifi cant correlations were found between other macroinvertebrate attributes (including family richness and evenness) and wood dimension, including diameter. However, analysis of covariance suggested that large wood supported a greater diversity and abundance of macroinvertebrates, indicat- ing that the method of analysis could infl uence the result. Adjustment for differences in sample dimension using rarefaction determined that these fi ndings were likely to be a result of the surface area and volumes sampled varying with the dimension of the wood. Per unit surface area, and per unit volume, small wood supported a similar number of families to large wood. Thus we conclude that, relative to the available surface area, small and large wood can be equivalent in their contribution to the available habitat in a stream. Therefore, the potential value of small wood as a habitat resource warrants its explicit consideration for inclusion in ecological and rehabilitation studies.

Using multiple lines of evidence to assess the risk of ecosystem collapse

Landscape classification and hydrological regionalisation studies are being increasingly used in ecohydrology to aid in the management and research of aquatic resources. We present a methodology for classifying hydrologic landscapes based on spatial environmental variables by employing non-parametric statistics and hybrid image classification. Our approach differed from previous classifications which have required the use of an a priori spatial unit (e.g. a catchment) which necessarily results in the loss of variability that is known to exist within those units. The use of a simple statistical approach to identify an appropriate number of classes eliminated the need for large amounts of post-hoc testing with different number of groups, or the selection and justification of an arbitrary number. Using statistical clustering, we identified 23 distinct groups within our training dataset. The use of a hybrid classification employing random forests extended this statistical clustering to an area of approximately 228,000 km2 of south-eastern Australia without the need to rely on catchments, landscape units or stream sections. This extension resulted in a highly accurate regionalisation at both 30-m and 2.5-km resolution, and a less-accurate 10-km classification that would be more appropriate for use at a continental scale. A smaller case study, of an area covering 27,000 km2, demonstrated that the method preserved the intra- and inter-catchment variability that is known to exist in local hydrology, based on previous research. Preliminary analysis linking the regionalisation to streamflow indices is promising suggesting that the method could be used to predict streamflow behaviour in ungauged catchments. Our work therefore simplifies current classification frameworks that are becoming more popular in ecohydrology, while better retaining small-scale variability in hydrology, thus enabling future attempts to explain and visualise broad-scale hydrologic trends at the scale of catchments and continents.

Modelling food-web mediated effects of hydrological variability and environmental flows

Effective ecosystem risk assessment relies on a conceptual understanding of ecosystem dynamics and the synthesis of multiple lines of evidence. Risk assessment protocols and ecosystem models integrate limited observational data with threat scenarios, making them valuable tools for monitoring ecosystem status and diagnosing key mechanisms of decline to be addressed by management. We applied the IUCN Red List of Ecosystems criteria to quantify the risk of collapse of the Meso-American Reef, a unique ecosystem containing the second longest barrier reef in the world. We collated a wide array of empirical data (field and remotely sensed), and used a stochastic ecosystem model to backcast past ecosystem dynamics, as well as forecast future ecosystem dynamics under 11 scenarios of threat. The ecosystem is at high risk from mass bleaching in the coming decades, with compounding effects of ocean acidification, hurricanes, pollution and fishing. The overall status of the ecosystem is Critically Endangered (plausibly Vulnerable to Critically Endangered), with notable differences among Red List criteria and data types in detecting the most severe symptoms of risk. Our case study provides a template for assessing risks to coral reefs and for further application of ecosystem models in risk assessment.