Document: THE-3-73-16

The impacts of exotic salt cedar (Tamarix ramosissima) on organic matter dynamics in a desert spring stream.

KENNEDY, T.A.*

University of Minnesota, St. Paul, MN 55108, USA ¹

Abstract:
Salt cedar (Tamarix ramosissima) is an exotic species that has become the dominant riparian tree along many rivers throughout the southwestern United States. Many studies have looked at the impacts of this species on the terrestrial environment, however few studies have addressed the impacts that this species has on rivers. Here I examined the impacts of salt cedar on organic matter dynamics in Jackrabbit spring, a small desert spring at Ash Meadows NWR in southern Nevada. Allochthonous litter inputs, litter retention, and litter decomposition rates in the stream were assessed in reaches within each of three different riparian vegetation types (native vegetation, salt cedar, experimental salt cedar removal) present along Jackrabbit spring. Bullrush (Scirpus americanus) litter dominates inputs to the stream in the native vegetation sites, salt cedar is the dominant input at salt cedar sites, and at experimental removal sites bullrush that has re-colonized since removal is the major input. Ash (Fraxinus velutina) is a minor component of litter inputs at all sites. Total litter inputs in native vegetation sites were significantly greater than in salt cedar sites which were greater than inputs in experimental removal sites. Litter retention is significantly higher in native vegetation sites than in salt cedar or experimental removal sites. ANCOVA was used to explore the relationship between decomposition rates of the three dominant litter inputs (ash, salt cedar, and bullrush) and vegetation type, water temperature, and stream velocity. Decomposition rates were highest for ash, followed by salt cedar , and then bullrush. Vegetation type significantly affected decomposition rates independent of the effects of temperature and velocity, with decomposition being more rapid in native sites than in either salt cedar or experimental removal sites. This study demonstrates that salt cedar has a variety of impacts on organic matter dynamics in Jackrabbit spring including a decrease in total allochthonous litter inputs, a change in the types of inputs from slow decomposing rushes in native sites to faster decomposing salt cedar in salt cedar sites, decreased litter retention, and a decrease in decomposition rates regardless of litter type.

Keywords: stream, biological invasion, organic matter dynamics, salt cedar, Tamarix

This abstract is being presented at: 4:00 PM in session:
Oral Session #67: Decomposition Processes.