Spatial dynamics of the vegetation community associated with an invasive emergent macrophyte in a regulated river.

Authors: Skaer Thomason, Meghan; Grewell, Brenda

Submitted to: Society of Wetland Scientists
Publication Type: Abstract Only
Publication Acceptance Date: 3/17/2017
Publication Date: 6/7/2017
Citation: Skaer Thomason, M.J., Grewell, B.J. 2017. Spatial dynamics of the vegetation community associated with an invasive emergent macrophyte in a regulated river.. Society of Wetland Scientists. [Abstract].

Interpretive Summary:

Technical Abstract: Successful management of riverine ecosystems often requires mitigation of alien plant invasions. Understanding how environmental variation within watersheds influences distribution and spread of invasive plants is essential to restoring impacted ecological functions and conserving native plant communities. Establishment and persistence of desired vegetation following weed removal requires knowledge of the spatial distribution of associated plant species and the relationship of the plant community to environmental conditions. Several regulated rivers in the United States and Europe are heavily invaded by Ludwigia hexapetala (Uruguayan primrose-willow), an emergent aquatic plant from South America whose clonal fragments disperse by hydrochory. Data critical for ecological restoration planning, including quantitative data on how plant communities vary with changing hydrogeomorphic conditions throughout invaded watersheds is often unavailable. We measured 12 environmental variables that influence plant growth and abundance, and recorded plant community composition associated with changes in distribution and abundance of L. hexapetala at two spatial scales in the Russian River, California. Multivariate ordination indicates plant species composition varied spatially and temporally and with environmental variables in invaded patches of L. hexapetala. Indicator species analysis revealed unique species were associated with study reaches, and these species changed through five years of study. Even though L. hexapetala is dominant in many invaded patches, the native annual herb Persicaria lapathifolia was an indicator species for river reaches characterized by reduced variability in hydrology. However, a perennial native grass (Leersia oryzoides) and native willow (Salix exigua) association were most prevalent in reaches not immediately upstream of impoundments. The species identified in these analyses may be candidates for further testing for use in reach-specific strategies for restoration of local vegetation communities. Studies like ours are a critical first step in development of effective restoration in complex watersheds.