Document Type

Thesis - University Access Only

Award Date

201

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

Abstract

In the last two decades the exotic plant sickleweed (Falcaria vulgaris Bemh., Apiaceae) has invaded, and come to dominate, large areas of the Fort Pierre National Grassland (FPNG) in central South Dakota, USA. Currently sickleweed is estimated to infest over 3200 ha of FPNG. The purpose of this study was to examine several of the biological and ecological traits that may contribute to the invasiveness of sickleweed in FPNG. Specifically, I researched germination characteristics of sickleweed seed collected from FPNG, the effect of sickleweed on other grassland vegetation in FPNG, and vegetative reproduction and regeneration of sickleweed from roots. Germination trials conducted at the SDSU Seed Testing Laboratory found that sickleweed seed had a high degree of germination (70-90%) in all tested conditions. Germination response was higher at cooler temperatures with no effect of light conditions or storage temperature (at P,:S0.05 level). Germination was significantly lower (at P,:S0.05 level) after 18 months of storage. In simulated field conditions with soil collected from FPNG, sickleweed had higher germination in bare soil taken from a patch of sickleweed than in vegetated, unclipped western wheatgrass soil (at P,:S0.05 level). Plot biomass data revealed that in dense sickleweed stands (>40 stems/m2), sickleweed (unclipped plots) reduced the biomass of all vegetation when compared to control (no sickleweed) plots (at P_::s0.05 level). Total biomass harvested from plots with sickleweed clipped at soil surface for one year was not significantly different (at P_::s0.05 level) than total biomass harvested from unclipped and control plots. Native grass biomass was significantly reduced (at P_::s0.05 level) by the presence of sickleweed in both treatment plots when compared to control plots. Biomass of introduced grasses and forbs was not significantly affected by treatments. To determine sickleweed root generative capacity, root segments, 4 cm in length, were cut from the proximal, middle, and distal portions of green house grown sickleweed taproots and buried under 5 cm of FPNG soil in a SDSU greenhouse. After 2 months shoot generation was high (68-82%) in all regions with no significant difference in response by portion of root (P=0.383), which suggests that sickleweed is capable of surviving taproot excision and generating new shoots from small portions of taproot. During the course of this experiment new shoot production from lateral roots was observed in greenhouse grown plants, a phenomenon not previously detected in the field. Lateral spread via rootstocks in a field setting was confirmed when sickleweed shoots began emerging in the second growing season up to 1 m away from potted sickleweed plants transplanted from FPNG into a local garden. The results of this study indicate that sickleweed at FPNG is a perennial plant with high germination capabilities, reproducing and spreading by sprouting from rootstocks, and negatively impacts the production of other vegetation, especially native grasses.

Library of Congress Subject Headings

Noxious weeds -- South Dakota -- Fort Pierre National Grassland

Sickleweed

Format

application/pdf

Number of Pages

87

Publisher

South Dakota State University

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