Large‐scale environmental flow results in mixed outcomes with short‐term benefits for a semi‐arid floodplain plant community

Abstract

Demonstrating and predicting the effectiveness of environmental watering to maintain ecosystem health is becoming increasingly important, notably in semi‐arid floodplain ecosystems. Modelling plant floodplain vegetation responses to inform environmental watering outcomes is also challenging. We evaluated the effects of a large‐scale environmental flow event on a semi‐arid floodplain lakeside plant assemblage for meeting the management goal of increasing water‐dependant taxa and functional groups. We developed a multi‐taxon Bayesian hierarchical model to describe temporal and small‐scale spatial patterns in taxonomic occurrences. We then examined community summary metrics (proportion of native taxa, plant functional groups) to evaluate patterns for the entire floodplain lakes system, the scale most relevant to management. Overall, in a system dominated by terrestrial dry plant taxa, 52.9% of terrestrial damp plant taxa showed a short‐term increase in occurrence in response to the environmental flow, which translated into similar responses in some functional groups. However, nearly half of the plant taxa that increased then demonstrated a decline by 18 months after the flow event. Our community summary metrics captured these general results; however, they were disproportionately influenced by a few abundant plant taxa. These results highlight the advantages of multi‐taxon models for interpreting flow responses and developing effective environmental flow management strategies, because they can be used to summarise community responses, while preserving important taxon‐specific information. In semi‐arid systems, where river regulation and climate change have reduced the frequency of flood events, the ability to deliver environmental flows during protracted periods of drought may be a policy option to restore or maintain the natural floodplain vegetation assemblage and prevents the transition to dryland taxa.

Flow‐mediated movement of freshwater catfish, Tandanus bostocki, in a regulated semi‐urban river, to inform environmental water releases

“…Environmental flows reinstate important aspects of the natural flow regime and support native fish populations by providing longitudinal connectivity of riverine habitats, flow-based cues for spawning and migration, riverfloodplain connection and suitable physical and hydraulic habitats (Arthington, 2012;King, Ward, O'Connor, & Green, 2010;. As the specific flow needs of different biota are quite variable (e.g., Beesley et al, 2014;Moxham, Kenny, Beesley, & Gwinn, 2018;Poff & Zimmerman, 2010), the development of appropriate flow regimes requires a robust understanding of flow-ecology relationships (Arthington, Naiman, Mcclain, & Nilsson, 2010;. In most instances, quantitative relationships are lacking and management is based on generic, often unvalidated, flow-ecology relationships derived from limited data sets or expert opinion (Davies et al, 2014;Gwinn, Beesley, Close, Gawne, & Davies, 2016).…”

Scientific integrity, public policy and water governance in the Murray-Darling Basin, Australia

“…The main claim for 'basin scale changes' is increased vegetation diversity, but the original data show high response variation at only a few sites (Capon and Campbell 2017) and there is no evidence provided by the authors to demonstrate these responses are more than short term. In fact, Moxham et al (2019) found only temporary, localised responses of floodplain plant communities to environmental watering. Gawne et al (2020) also reported mostly short term, localised responses, stating: 'the monitoring programme is showing promise with short-term responses being observed and longterm patterns being recorded', but presented no evidence of long-term patterns.…”

Flow to nowhere: the disconnect between environmental watering and the conservation of threatened species in the Murray–Darling Basin, Australia

“…For example, increased vegetation diversity was recorded at only a few sites and these showed highly variable responses (Capon and Campbell 2017). Moxham et al (2019) found only temporary, local responses by floodplain plant communities to environmental watering. Gawne et al (2020) reported short-term, localised responses, stating that 'the monitoring program is showing promise with short-term responses being observed and long-term patterns being recorded', but presented no evidence for the latter claim.…”