Declining survival across invasion history for Microstegium vimineum.

Many alien species become invasive because they lack coevolutionary history with the native community; for instance, they may lack specialized enemies. These evolutionary advantages may allow the invader to establish and persist when rare within a community and lead to its monodominance through positive frequency dependence, i.e. increasing per capita population growth rate with increasing frequency of conspecifics. However, this advantage could degrade through time due to evolutionary and ecological changes in the invasive and native plant and microbial communities. We investigated survival rates and individual biomass as proxies for per capita population growth rates for the invasive grass, Microstegium vimineum, across a gradient of conspecific frequencies (10-100% relative cover of M. vimineum) within 12 sites that varied in time since invasion. We expected M. vimineum frequency dependence to become more negative and its proxies for population growth at low conspecific frequency to decline across invasion history. We also explored the belowground fungal community associated with M. vimineum, since we hypothesized that changes in M. vimineum population dynamics may result from shifting microbial interactions over time. Microstegium vimineum frequency dependence changed from negative to neutral across invasion history and the shift was driven by a decline in survival at low frequency. Changes in M. vimineum root fungal community were associated with time since invasion. Our results do not support a shift in frequency dependence from positive to negative across invasion history. However, our results suggest M. vimineum populations may be less prone to persist at older invaded sites and thus more vulnerable to management intervention

The final model terms of the model with the lowest AIC value.

<p>The final model terms of the model with the lowest AIC value.</p

Survival across time since invasion and <i>Microstegium vimineum</i> frequency.

<p>Contour plot of proportion of <i>Microstegium vimineum</i> survivors across <i>M</i>. <i>vimineum</i> spring frequency and time since invasion of each of the 12 sites (n = 82).</p

Map of <i>Microstegium vimineum</i> invasion history.

<p>Points on map represent the 12 sites where the study was performed and are also listed in the table with their abbreviated identification, state of location, and estimated time since invasion. Inset map of the United States depicts the location of the invasion history map.</p

Innovative traffic control technology and practice in Europe.

Federal Highway Administration, Office of International Programs, Washington, D.C.Mode of access: Internet.Author corporate affiliation: American Trade Initiatives, Alexandria, Va.Subject code: CICSubject code: EMSubject code: FGFSubject code: HBSubject code: HBECSubject code: HBEESubject code: IEBSubject code: KNSubject code: FSSubject code: PMMOSubject code: WOHSubject code: WW*I

Workshop on Field Inspection and Rehabilitation of Traffic Control Devices - Proceedings

DTFH61-69-C-00058The Federal Highway Administration (FHWA) has begun a number of initiatives to improve signing on the Nation's roadways. These include workshops to obtain input from experts across the country, a review of each State's highway sign replacement and refurbishing program, and a training course. This report documents the proceedings of the workshops, one held in the Western United States and one in the Eastern United States. The workshops opened with a plenary session on Issues, Needs, and the FHWA Research Program, followed by a plenary session on Development of Minimum Requirements. The program continued with a panel discussion on Performance Standard Criteria, followed by a plenary session on Materials Selection. Breakout sessions on freeway signing, non-freeway signing, and motorist services and tourist-oriented signing completed the first day of the workshops. The second day opened with reports of the breakout sessions and continued with a plenary session on Field Assessment Techniques. A plenary session on Maintenance Procedures and Programs followed. The second day ended with breakout sessions on sign replacement methods, using contracting versus in-house and prison industries, and traffic control during sign replacement. The third day opened with reports on the previous day's breakout sessions, followed by a plenary session on Improved Inventory Techniques. The workshops closed with a look to the future plenary session. This report details the remarks made by the panelists and the comments and concerns of the participants on each of these issues