Alterations in flood frequency increase exotic and native species richness of understorey vegetation in a temperate floodplain eucalypt forest

Abstract

The delivery of environmental flows for biodiversity benefits within regulated river systems can potentially contribute to exotic weed spread. This study explores whether exotic plants of a floodplain forest in Victoria, Australia, are characterised by specific functional groups and associated plant traits linked to altering hydrological conditions over time. Permanently marked 20 9 20 m 2 plots from five wetland sites in Eucalyptus camaldulensis floodplain forest were sampled twice, first in the early 1990s (1993)(1994) and then 15 years later (2007)(2008). Species cover abundance data for understorey vegetation communities were segregated by season and analysed using ordination analysis. Exotic species richness was modelled as a function of site flooding history and native species richness using general linear models. Site ordinations by detrended correspondence analysis showed differential community compositions between survey dates, but native and exotic species were not clearly differentiated in terms of DCA1 scores. Most exotics belonged to functional groups containing annual species that germinate and reproduce under drier conditions. Exotics reproducing under wetter conditions were in the minority, predominantly perennial and capable of both sexual and asexual reproduction. Site flooding history and native species richness significantly predicted exotic species richness. Vegetation changes are partially structured by reduced flood frequency favouring increased abundance of exotic, sexually reproducing annuals at drier sites. Sites of low flood frequency are more sensitive to future exotic weed invasion and will require targeted management effort. Flow restoration is predicted to benefit propagule dispersal of species adopting dual regeneration strategies, which are predominantly natives in this system.

Effects of flood timing and livestock grazing on exotic annual plants in riverine floodplains

“…These experimental results support conclusions from surveys and modelling studies that floods provide an effective method to control exotic annuals on river floodplains (Stokes, Ward & Colloff ; Catford et al . ), in the short term at least.…”

“…This ‘terrestrialization’ hypothesis (Catford et al . ) posits that annual, terrestrial exotic plants have invaded floodplains following a reduction in the frequency, magnitude and duration of floods (Stokes, Ward & Colloff ; Catford et al . ).…”

“…Consequently, it is imperative that environmental allocations are well targeted. While flooding has been suggested as a practical method to control exotic annuals (Stokes, Ward & Colloff ; Catford et al . ), no experimental data are available on how floods in different seasons affect exotics.…”

Vascular Plants Distribution as a Tool for Adaptive Forest Management of Floodplain Forests in the Dyje River Basin

“…Sites of low flood frequency are more sensitive to future exotic weed invasion and will require targeted management effort. Flow restoration is predicted to benefit propagule dispersal of species adopting dual regeneration strategies, which are predominantly native species in this system (Stokes et al 2010). The invasion by alien plant species is a major challenge to the conservation and management of riparian areas which can alter ecosystem structure and function in undesirable ways (Hood and Naiman 2000;Stohlgren et al 1998).…”

Floodplain vegetation of the River Murray in 1987–1988: an important pre-drought benchmark for subsequent studies.

“…Recent studies have indicated that reduced flooding as a result of river regulation and water extraction has favoured exotic species (Stokes et al 2010, Catford et al 2011. However, other disturbance factors, including agricultural activities, urban development, recreational activities and logging, have also promoted weed invasion.…”