1a. Objectives (from AD-416):
Human impacts on the environment are altering species composition in many of the nation's national parks. One such impact is the increase in invasive plant species which are quickly over-running many of the native plant species. One such invasive species is Japanese stiltgrass (Microstegium vimineum). The objective of the current research is to quantify human impacts, particularly nitrogen deposition, carbon dioxide and light on the ability of this species to grow and propagate.
1b. Approach (from AD-416):
Working with the National Park Service’s Center for Urban Ecology, we will obtain local seed from stiltgrass populations and determine growth and seed production utilizing a range of nitrogen deposition rates and carbon dioxide concentrations under glasshouse and growth chamber conditions. Data will be utilized in a multiple regression model in order to ascertain whether human induced changes in macroclimate near the D.C. area will contribute to the perniciousness of this invasive species.
3. Progress Report:
Near roadside and forest weather stations were established at Catoctin National Park and the USDA Beltsville Area Research Center (BARC) during 2010. These were set up to determine the influence of anthropogenic change on the establishment and success of Microstegium vimineum (Japanese Stiltgrass), an invasive weed of national parks in the Eastern United States. From 2010 through 2012, Microstegium vimineum establishment and reproductive fitness was measured in fixed quadrants in close proximity to the weather stations. Initial infestation at these sites was quite high with seedling densities between 320 to 560 plants per m2. Eighteen 50-m long transects were laid out along the road that the weather stations were located near. Those 18 transects were placed within 2 km of the weather stations along the same road and were deliberately placed in a range of sites where land-use legacy varied. Using 1937 aerial imagery, transects were placed in sites that were in agricultural use (fields were clearly evident in the images) and have since reverted to forest. Transects were also placed in places that were in forest in 1937 and have remained in forest since. In addition to field measurements, additional studies utilizing three different Microstegium populations (Catoctin National Park, Central Pennsylvania, and Maryland Eastern Shore), two light levels (0.5 and 0.1 of full sun) and two levels of Nitrogen input (1.0 and .1x Hoagland’s) were established in the greenhouse to quantify biomass and seed production. Analysis of both field and greenhouse experiments is ongoing. Initial visual observations have suggested that deer over-abundance is also enhancing Microstegium success. While deer abundance is being experimentally manipulated, work at other sites in the park strongly point to deer as an important factor. To this end, ARS PIs joined a representative of the National Park Service along with their group in assessing deer exclosures located throughout the park. Where Microstegium was in close proximity to the exclosure, deer exclosures were significantly less invaded than deer browse plots. In addition to monitoring the Catoctin exclosure plots ARS has been fortunate to obtain data from nine National Parks sites where deer exclosure studies are ongoing and are currently analyzing those data to assess the Microstegium invasion pattern across those sites. The Microstegium population by nitrogen by light interactive greenhouse studies are finished. These data were analyzed and a peer-reviewed article was submitted to the Biological Invasions journal in May, 2013. Initial analysis indicated that the eighteen transects placed in sites with an agricultural land-use legacy had approximately 10-fold higher populations and those populations extended further from the road. Initial analysis also suggests that deer exclosures may allow recurrence of different species other than Microstegium; however a complete analysis of plant demographics is ongoing. It is anticipated that there will be at least two peer-reviewed publications from Catoctin, one on changes in plant demographics with the deer exclosures, the other on near-road abiotic conditions related to the potential establishment of Microstegium. A third publication, on the assessment of light and nitrogen deposition on the growth and seed production of different Microstegium populations collected in Maryland and Pennsylvania, has been submitted to the journal of Biological Invasions.