Early detection of an invading nonindigenous plant species (NIS) may be critical for efficient and effective management. Adaptive survey sampling methods may provide unbiased sampling for best estimates of distribution of rare and spatially clustered populations of plants in the early stages of invasion. However, there are few examples of these methods being used for nonnative plant surveys in which travelling distances away from an initial or source patch, or away from a road or trail, can be time consuming due to the topography and vegetation. Nor is there guidance as to which of the many adaptive methods would be most appropriate as a basis for invasive plant mapping and subsequent management. Here we used an empirical complete census of four invader species in early to middle stages of invasion in a management area to assess the effectiveness and efficiency of three nonadaptive methods, four adaptive cluster methods, and four adaptive web sampling methods that all originated from transects. The adaptive methods generally sampled more NIS-occupied cells and patches than standard transect approaches. Sampling along roads only was time-efficient and effective, but only for species with restricted distribution along the roads. When populations were more patchy and dispersed over the landscape the adaptive cluster starting at the road generally proved to be the most time-efficient and effective NIS detection method.

We developed a protocol for categorizing nonnative plants according to their negative impacts on biodiversity in a large area such as a state, nation, or ecological region. Our objective was to provide a tool that makes the process of identifying, categorizing, and listing nonnative plants that cause negative impacts to biodiversity analytic, transparent, and equitable and that yields lists that are useful to researchers, land managers, regulators, consumers, and commercial interests such as the nursery industry. The protocol was designed to distinguish between species that cause high, medium, low, or insignificant negative impacts to native biodiversity within the state, region, or nation of interest. It consists of 20 multiple-choice questions grouped into four sections, which each address a major aspect of a species' total impact and when combined yield an overall “Invasive Species Impact Rank” or “I-Rank” (high, medium, low, or insignificant). The nonprofit organization NatureServe is now using this protocol to assess the estimated 3,500 nonnative vascular plant species that are established in the United States to create a national list prioritized by negative impact on biodiversity. The protocol and additional information are available on the Internet at http://www.natureserve.org/getData/plantData.jsp, and over 500 completed species assessments are available through NatureServe Explorer (http://www.natureserve.org/explorer/).

The widespread recognition that nonnative plants can have significant biological and economic effects on the habitats they invade has led to a variety of strategies to remove them. Removal alone, however, is often not sufficient to allow the restoration of altered communities or ecosystems. The invasive plant's effects may persist after its removal thus exerting a “legacy” that influences community composition or the ecosystem properties or both over some ensuing period. Here, we review evidence of such legacy effects on plant and soil communities, soil chemistry, and soil physical structure. We discuss this evidence in the context of efforts to restore community composition and ecosystem function in invaded habitats. Legacies are especially likely to develop in cases where invasive species cause local extirpations of resident species, alter resource pools, and interact with other aspects of global change including land-use changes, atmospheric N deposition, acid rain, and climate change. In cases where legacies of invasive plants develop, the removal of the nonnative species must also be accompanied by strategies to overcome the legacies if restoration goals are to be achieved.