There is a well-documented association between anthropogenic disturbance and non-indigenous plant invasions. Many U.S. Army and other Department of Defense (DoD) lands have been subjected to varying degrees of disturbance. Non-indigenous invasive plant species (NIPS) are recognized as a widespread problem on DoD and other Federal lands, as well as on state and private lands. Non-indigenous invasive plants dominate millions of acres throughout the country, but particularly in the west. These invasions have had many effects including reduced (and sometimes eliminated) native plant and animal diversity, decreased community productivity, altered fire regimes, altered nutrient cycling, and altered community structure and function. Additionally, non-indigenous, invasive, exotic, and noxious plants degrade native habitats, alter ecosystems and ecological processes, and result in large agricultural economic losses.

This research is aimed at the problems of managing and controlling the spread of NIPS on DoD and other lands. This work examined the response of native grass populations to long-term presence of NIPS. As remnants of native communities subjected to the NIPS Russian knapweed (Rhaponticum repens), two native grass species common to western DoD lands were identified, alkalai sacaton and needle and thread grass. Specific objectives of this work were to: identify native grasses that may be more resilient to NIPS; to identify attributes of the experienced native plant populations that contribute to resilience and resistance to the competitive effects of NIPS; to identify genetic markers and phenotypic traits that confer superior competitive ability; and to determine if those phenotypic traits are transmitted to subsequent generations of the native grasses.

This study was designed to test competitive abilities of native grass populations differing in NIPS invasion history (invaded and non-invaded). Maternal grass individuals were collected to examine the influence of the invasions on population genetics and phenology of the two species. In controlled laboratory and field settings, this research examined the growth, seed production, and germination of the two grasses in competition with Russian knapweed and the NIPS Canada thistle and genetic variability of the two grasses via amplified fragment length polymorphism and Inter-Simple Sequence Repeat analyses.

The results of this research provides multiple lines of evidence that lineages of alkali sacaton, and to a lesser degree needle and thread, collected from within (IN) invaded sites of Russian knapweed, differ from lineages collected outside of (OUT) invaded sites. Indications are that these differences translate into differences in competitive ability. This research also provides evidence that differences in competitive ability toward the knapweed invader may also apply to other NIPS, in this instance Canada thistle. This research also provides evidence of differences in competitive performance of differing IN and OUT genotypes. Because needle and thread was not as competitive with Canada thistle, the results agree with other published research that warm-season plants have a competitive advantage over cool season species.

This project developed a Biological Screening Process to assist managers with selecting promising genotypes. This research developed an effective way to comparatively evaluate the performance of differing and disparate genotypes and to select for the most promising genotypes for further and expanded study evaluation.

The impacts of NIPS on native plant populations and their potential use for restoration are poorly understood. However, native grasses that remain following long-term exposure to invading species may better tolerate weed presence than nonexposed natives. Such invasion experienced native plants can be more competitive with invaders but are often excluded as restoration materials. Planting native species with invasive history may augment biodiversity and in turn, increase native ecosystem resistance and resilience to invasion. Native seed collection may be enhanced by including invasion-experienced native plant populations. The native seed production industry can use this research to develop seed collection protocols to included remnant native populations and production techniques that ensure competitive traits are not being lost from native accessions.