Environmental water allocations are insufficient to control an invasive wetland plant: evidence from a highly regulated floodplain wetland

Abstract

Summary1. Regulation of the world's rivers and alteration of natural flow regimes have led to the degradation of floodplains and wetlands. Here, we investigate plant-flood interactions in a floodplain wetland to determine whether a return to more natural flooding regimes using environmental water allocations can contribute to restoration from a degraded state. 2. We use detailed field surveys to quantify the effects of flooding on a native rush, Juncus ingens, which has become invasive in floodplain grasslands in south-eastern Australia. We then apply these results to determine the likelihood of generating the flood regime required to control J. ingens in its new range, considering the regulated nature of the river system. 3. Complete submergence for several months substantially reduced J. ingens stem densities, survival and recovery. However, rhizomes were able to survive, with new stems produced during subsequent partial submergence. Under current regulated conditions, the volume of environmental water needed to cause substantial stem decline, and potentially rhizome death, is extremely large -particularly for tall stems -even when used in conjunction with a natural flood peak. 4. Synthesis and applications. Although repeated submergence events may cause stem decline of the invasive plant Juncus ingens, the present day operational constraints of the regulated river make it difficult to deliver the required volume and depth of water using environmental water allocations. Furthermore, shallow floods may actually provide favourable conditions for growth. This research is particularly relevant for other restoration projects where historical disturbance regimes can only be partially mimicked. Whilst a managed flood regime can be successful in achieving a range of conservation and restoration goals, there may be situations in which river regulation can limit the ability to effectively manage particular species using environmental water allocations alone.

Anomalous droughts, not invasion, decrease persistence of native fishes in a desert river

“…In contrast, most riparian studies have found that hydrology supersedes species interactions – flow alterations preclude native species and promote the dominance non‐native species, with little effect of non‐natives on natives (Nagler et al ., ; Stromberg et al ., ,b). Within this context, recent work has suggested that successful management of native riparian plant communities may be achieved by mimicking –if water allocations permit – natural disturbance regimes (Catford et al ., ; Vivian et al ., ). Consistent with this riparian work, we found support for the notion that discharge variation was paramount and superseded species interactions in determining community composition at multiple scales.…”

“…We used this approach to show how anomalous floods and droughts can influence long-term trajectories of native fish in highly variable rivers that have been invaded by non-native faunas. This topic has been the focus of a considerable amount of research in both riverine (e.g., Seegrist & Gard, 1972;Bernardo et al, 2003;Propst et al, 2008;Gido & Propst, 2012) and riparian ecosystems (e.g., Sher et al, 2002;Nagler et al, 2005;Stromberg et al, 2007a,b;Catford et al, 2011;Vivian et al, 2014). Generally, the riverine studies suggest that hydrology is an important driver of abundance of both natives and non-natives (Seegrist & Gard, 1972;Bernardo et al, 2003;Propst et al, 2008) and that Table 1).…”

Belowground bud bank of invasive plants contributes to their successful invasion in coastal wetlands

“…Belowground bud bank serves as the basis for vegetative reproduction, and the size and composition of belowground bud bank play an important role in determining the potential composition of the plant community (Wu et al 2021). Previous studies have shown, at the species level, that invasive alien plants benefited more from clonal traits, such as clonal integration and clonal foraging, than native plants in heterogeneous environments (Vivian et al 2014; Liu et al 2017; Wang et al 2017). However, at the community level, little is known about whether belowground bud bank can help invasive alien plants to successfully invade in native plant communities.…”