Controlling Plant Invaders

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M. vimineum is a highly successful annual invasive grass found throughout eastern U.S. forests that thrives in a variety of habitats, including dry, open areas; moist riparian zones; and under the tree canopy. It tends to outcompete and out crowd native vegetation, altering the soil microbial community and nitrogen mineralization rates. This causes acceleration in nitrogen and carbon cycling, which leads to decreased litter accumulation and soil organic material, conditions that further encourage its spread at the expense of native vegetation.

Invasive species are changing the structure and function of our native ecosystems, there is a need for effective management of these species to protect ecosystem services and biodiversity. Through a desk study which collated all published research on the primary plant invader of forests across 25 U.S. states, Microstegium vimineum, Coweeta researchers showed how ecological theory can be used to inform land management; most importantly, that metapopulation theory can be used to focus management on specific areas where the invader grows well, and that eradication of the invader from these areas should reduce its abundance across the entire landscape by removing the source of its seeds.

The fact that M. vimineum does well in moist riparian and understory habitats initially surprised researchers, as the grass employs the C4 photosynthetic pathway generally considered an adaptation for dry environments and commonly associated with invaders of open habitat. Coweeta researchers synthesized all available information on the species’ life history and habitat characteristics with the goal of understanding of how the unique invader’s niche requirements affect its population dynamics, and how an understanding of these population dynamics through space and time could produce better management recommendations.

Their approach was unique in two ways: it did not use landscape position as a proxy for niche requirements and it emphasized stage-specific investigation of niche limitations. Using landscape position as a proxy for niche requirements fails to elucidate subtle differences in habitat requirements, such as light or soil moisture, that vary over heterogeneous landscapes. Emphasizing stage-specific habitat requirements allows researchers to differentiate varying needs during germination, growth, and reproduction, helping to elucidate temporal variation in population dynamics. In the case of M. vimineum, researchers were able to discover that the grass was able to disperse and thrive along sunny and sometimes wet roadside habitats, which then acted as a source population for interior sink populations- those in the interior of the forest- that would otherwise not be able to sustain themselves from year to year. Though the habitat conditions under the canopy were sufficient to allow growth and survival for the year, they were not adequate for seed production and dispersal. Overall, this research demonstrates that identification of niche requirements, specifically as they vary over key demographic stages (recruitment, survival, growth, reproduction, and dispersal), can be useful to identify effective and efficient management strategies- in the case of M. vimenium of focusing eradication strategies on source populations.

Figure. Mean differences (+/- 95% CI) in soil moisture (%, Moist), diffuse light (%, Light), temperature (°C, Temp), leaf litter (%, Litter), herbaceous cover (Herb, g m-2), soil clay content (Clay, %) and soil pH between plots invaded and uninvaded by M. vimineum as measured at the Coweeta LTER and two other sites. Confidence intervals that do not cross zero (indicated by the dashed line) indicate statistically significant differences in means.
Warren et al. 2011
For further reading: 
Warren, Robert J., Justin P. Wright, and Mark A. Bradford. 2010. The putative niche requirements and landscape dynamics of Microstegium vimineum: an invasive Asian grass. Biological Invasions.
Strickland, Michael S., Jayna L. DeVore, John C. Maerz, and Mark A. Bradford. 2010. Grass invasion of a hardwood forest is associated with declines in belowground carbon pools. Global Change Biology 16:1338-1350.
Warren, Robert J., Volker Bahn, Timothy D. Kramer, Yaya Tang, and Mark A. Bradford. 2011. Performance and reproduction of an exotic invader across temperate forest gradients. Ecosphere 2(2): Article 14.
For further information: 
Dr. Robert J. Warren
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