PoTenTIAl IMPACTS oF yeAr-roUnD SAMPlInG on MonITorInG PreSenCe- ABSenCe oF InvASIve FlorA In THe SoUTHern UnITeD STATeS

Studies suggest that the southern United States is an area of primary concern with regards to the spread of nonnative invasive plant species. Recent data show that species such as Japanese honeysuckle (Lonicera japonica) and Nepalese browntop (Microstegium vimineum) are invading forests and displacing native species throughout the southern United States. Monitoring on large spatial scales is among the most important mechanisms for the detection and prevention of the spread of nonnative species. Accurate assessments of on-going biological invasions are a primary research priority in the Southeast. As one method for addressing this need, the US Forest Service Southern Research Station (SRS), in partnership with State forestry agencies across the South, initiated a southern region survey of 33 invasive plant taxa in 2001 on all forest ownerships as part of the SRS Forest Inventory and Analysis (FIA) program. Currently in the southern United States, presence-absence data is collected for select invasive flora throughout the calendar year. Little is known about the impacts of year-round sampling on the quality of invasive flora data collection. In this study we investigate the implications of year-round sampling on presence-absence data collected by the southern FIA program for states east of the Mississippi river. Chinese and European privets (Ligustrum spp) are observed on FIA plots most often between February and May, and least often between September and December. Exotic roses (Rosa spp) and Japanese honeysuckle follow a similar trend. Nepalese browntop, however, is observed more often between August and October. Moreover, Nepalese browntop is observed more than four times as often during peak months than it is during the period between December and April. These results suggest that plant apparency may be impacting the quality of presence-absence data collected by the SRS-FIA program. While the systematic nature of the FIA sampling design minimizes the impact to population estimates of sampled invasive flora, year-round sampling may be impacting attempts to accurately portray the geographical distribution of a given plant.