Dissertation Research: Understanding the Differential Success of Invasive and Naturalized Populations of Bromus tectorum L. (Cheatgrass, downy brome)

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Plants introduced into new ranges are often more vigorous and invasive than they are native ranges. To explain these differences, several hypotheses relating to new environments have been proposed. This research tests an alternative hypothesis: that differences in vigor and seed production may be due to genetic differences in the plants themselves. The annual cheatgrass was introduced into New Zealand and North America over 100 years ago with radically different results. In the southern part of New Zealand's South Island, it persists at low levels; in western North America, it dominates vast areas. In four greenhouse environments, 62 populations from native areas in Europe and the introduced regions were compared. North American populations were most vigorous (tallest, greatest vegetative and reproductive weights), followed by European, then New Zealand populations. This supports the hypothesis that invasive or non-invasive performance can be genetically based and differ from region to region. Seed germination trials are planned, as is DNA fingerprinting to directly compare introduced populations and their native relatives. The question of what makes a species invasive has been critical in agriculture and natural resource management for decades, but is still not well-understood. This research addresses that question and has important implications for screening potential invaders and controlling cheatgrass and other weeds.