Jarrod Kath

Relative influence of habitat modification and interspecific competition on woodland bird assemblages in eastern Australia

Abstract Many of eastern Australias woodland birds have declined in recent decades. Although historical landscape transformation ultimately underlies these declines, effective conservation action requires knowledge of the relative importance of current threats to woodland birds. Through a literature review and analysis of empirical data from seven woodland regions, we investigated the relative importance of habitat structure, site context and aggressive avian competitors (miners, Manorina spp.) for woodland birds in eastern Australia. The literature review revealed that the factor which most consistently influenced the richness, abundance and assemblage composition of woodland birds was the density or presence of Manorina honeyeaters. A positive effect of site structural complexity was also often reported, but the effects of area, isolation and grazing varied among the reviewed studies. Across the seven empirical datasets, density of Manorina honeyeaters was responsible for the great majority of the independently explained variance in all but one region. We conclude that interspecific competition with Manorina honeyeaters is one of the most important and widespread processes threatening woodland birds in eastern Australia. In regions where this threatening process is prevalent, the greatest conservation gains for woodland birds may therefore be achieved by focussing on reducing habitat suitability for aggressive Manorina honeyeaters.

Discretization of continuous predictor variables in Bayesian networks

Bayesian networks (BNs) are a popular tool in natural resource management but are limited when dealing with ecological assemblage data and when discretizing continuous variables. We present a method that addresses these challenges using a BN model developed for the Upper Murrumbidgee River Catchment (south-eastern Australia). A selection process was conducted to choose the taxa from the whole macroinvertebrate assemblage that were incorporated in the BN as endpoints. Furthermore, two different approaches to the discretization of continuous predictor variables for the BN were compared. One approach used Threshold Indicator Taxa Analysis (TITAN) which estimates the thresholds based on the biological community. The other approach used was the expert opinion. The TITAN-based discretizations provided comparable predictions to expert opinion-based discretizations but in combining statistical rigor and ecological relevance, offer a novel and objective approach to the discretization. The TITAN-based method may be used together with expert opinion. We propose the empirical estimation of thresholds to discretize continuous predictor variables within Bayesian networks.We used a case study to illustrate it.Predefined criteria were used to select five macroinvertebrate taxa that were incorporated in the BN as endpoints.Continuous predictor variables were discretized using Threshold Indicator Taxa Analysis (TITAN).TITAN-based discretizations provided comparable predictions to expert opinion-based discretizations.

Why groundwater matters: an introduction for policy-makers and managers

ABSTRACT In many parts of the world the combined pressures of population growth and a drying climate have resulted in the proliferation of water focused policies which aim to increase the resilience of socio-ecological systems. Until recently, these policies often reflected surface water centric views of water resources, with groundwater receiving scant attention. In this paper we provide an introduction to the importance of groundwater for water-dependent socio-ecological systems and why it needs to be better incorporated into environmental water management policies. Specifically we highlight the key role of groundwater in buffering the environment and socio-economic activities against drought. We also outline some of the key challenges that face policy-makers and managers implementing groundwater management policies. These include dealing with groundwater resources that are spatially and temporally mismatched with surface water resources; transboundary governance issues; challenges between focusing on either preventative or restorative actions and most importantly limited knowledge about groundwater resources and groundwater–ecology relationships. We hope that the information in this paper will assist in the development of sustainable surface-groundwater water management policies, as well as highlight important challenges that should be considered before implementing groundwater related policies.

Groundwater salinization intensifies drought impacts in forests and reduces refuge capacity

1. Shallow groundwater aquifers regularly support drought refuges for water-dependent ecosystems. However, many aquifers are impacted by over-extraction and pollution, potentially degrading their ability to support groundwater-fed drought refuges. 2. We investigated the response of groundwater-connected riverine forests to a drought considered equivalent in intensity to those predicted under severe climate change for 2030. The drought’s impact was investigated in an area where shallow groundwater resources are heavily exploited and polluted by salinization. 3. We used remotely sensed vegetation productivity (enhanced vegetation index) data from a long-term data set (2000–2011) at 475 riverine forest sites in the Campaspe catchment, southeastern Australia. Generalized additive mixed models and boosted regression trees were used to model the relationship between groundwater and other environmental covariates with forest change during drought. 4. Models explained up to 44% of the variation in forest change during drought. Forests underwent the greatest declines in areas of high salinity (>6000 lS cm-1) associated with shallow groundwater depths (0–5 m). Conversely, forests in areas of lowest salinity (<2000 lS cm-1) and groundwater depths of more than 7-5 m showed the least decline during drought. 5. In landscapes where groundwater quality is not compromised, previous studies have shown that shallow groundwater provides important drought refuges and refugia. Here, we show that when groundwater salinization has occurred, forests connected to shallow groundwater are more vulnerable to drought. In effect, salinization reduces the capacity of groundwater-connected habitats to function as drought refuges. 6. Synthesis and applications. Currently, there is an emphasis on managing environmental flows to support freshwater ecosystems and associated forests under water stress. However, delivery of environmental water is restricted to areas within a linear stream network and there is often limited capacity to deliver environmental flows during drought. Alternatively, a focus on drought refuges and refugia and processes important for maintaining groundwater quality (e.g. catchment revegetation to reduce shallow groundwater salinization) may better allow drought effects to be managed across a catchment, without directly focusing on highly contested surface water resources.

A conceptual framework for ecological responses to groundwater regime alteration (FERGRA): Ecological responses to altered groundwater regimes

Globally, the provision of groundwater‐supported ecosystem services is threatened by climate change, water extraction, and other activities that alter groundwater regimes (defined as temporal dynamics in groundwater pressures, storage, and levels). Research on how altered groundwater regimes affect the ecology and ecosystem services of diverse groundwater‐dependent ecosystems (GDEs) is currently fragmented with little integration across different GDEs, hampering our ability to understand and manage ecological responses to anthropogenic changes to groundwater regimes. To address this, we present a framework for assessing ecological responses to groundwater regime alteration (FERGRA). FERGRA is a logical approach to investigating how alterations to groundwater regimes change the timing, variability, duration, frequency, and magnitude of groundwater connections to different GDEs, in turn affecting their ecological processes and ecosystem service provision. Using FERGRA, multiple GDEs can be assessed concurrently, optimizing their integrated management. Unifying the concepts of ecological responses to altered groundwater regimes and groundwater connections of different GDEs across the landscape, FERGRA provides a framework for (a) organizing the currently fragmented research on GDEs to better identify commonalities and knowledge gaps, (b) formulating and testing hypotheses for quantifying ecological responses to groundwater regime alteration in GDEs to derive general principles to guide research and management, and (c) facilitating assessments of the trade‐offs between the benefits of groundwater extraction (e.g., to support mining and agriculture) versus conservation of GDEs to protect other ecosystem services.