Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Abstract

Riparian zones are formed by interactions between fluvio-geomorphological processes, such as sediment deposition, and biota, such as vegetation. Establishment of invasive alien plant (IAP) species along rivers may influence vegetation dynamics, evidenced as higher seasonal or inter-annual fluctuations in native plant diversity when IAP cover is high. This could impact the overall functioning of riparian ecosystems. Conversely, fine sediment deposited in riparian zones after floods may replenish propagule banks, thus supporting recruitment of native species. The interactive effects of invasion and fine sediment deposition have hitherto, however, been ignored. Vegetation surveys across rivers varying in flow regime were carried out over 2 years to assess changes in community composition and diversity. Artificial turf mats were used to quantify over-winter sediment deposition. The viable propagule bank in soil and freshly deposited sediment was then quantified by germination trials. Structural Equation Models were used to assess causal pathways between environmental variables, IAPs and native vegetation. Greater variation in flow increased the cover of IAPs along riverbanks. An increased in high flow events and sediment deposition were positively associated with the diversity of propagules deposited. However, greater diversity of propagules did not result in a more diverse plant community at invaded sites, as greater cover of IAPs in summer reduced native plant diversity. Seasonal turnover in the above-ground vegetation was also accentuated at previously invaded sites, suggesting that a legacy of increased competition in previous years, not recent sediment deposition, drives above-ground vegetation structure at invaded sites. The interaction between fluvial disturbance via sediment deposition and invasion pressure is of growing importance in the management of riparian habitats. Our results suggest that invasion can uncouple the processes that contribute to resilience in dynamic habitats making already invaded habitats vulnerable to further invasions.

All change at the water’s edge: invasion by non-native riparian plants negatively impacts terrestrial invertebrates

“…In our study, both F. japonica cover and I. glandulifera cover showed strong negative associations with Simpson's invertebrate diversity and total invertebrate abundance compared to other environmental variables, in both sampling months. This supports the ability of INNP to impose structural changes on riparian habitats during their period of peak biomass (Pattison et al 2017;Greenwood et al 2018), as well as during the preceding months when INNP stands are developing. Loss of native plant species from invaded sites may deplete invertebrate assemblages that specialise on Fig.…”

Interacting effects of climate change and invasions by alien plant species on the morphodynamics of temperate rivers

“…Loss, replacement or displacement of native plant species by IAPS can potentially alter biogeomorphic phenomena by directly increasing or decreasing sediment erosion or deposition and consequently influencing the locations and forms of emerging landforms (Fei et al, 2014; Tickner et al, 2001). The potential landform building impacts of such invasions are complex because they are related to feedbacks between biological and geomorphological components at various timescales (Pattison et al, 2018) but consideration of the impact of climate‐environmental change on river morphodynamics needs to reflect the degree to which IAPS might take over the river engineering role of native species.…”

The Impact of Invasive Aliens Species of Plant in Dryland Crop Production

“…The statement was supported by Gross et al [29] which states that an estimated more than 85% of plants in the world take the role of insect pollinators. Pattison et al [30] stated that the presence of invasive alien plants can affect vegetation dynamics. Broadly speaking invasive plant interactions with ecosystems tend to be negative.…”