Non-Native Plant Survey at Grant-Kohrs Ranch National Historic Site

Wood, Shana; Rew, Lisa

This report presents the results of a non-native plant survey performed in Grant-Kohrs Ranch National Historic Site (GRKO) in 2003. The purpose of the survey was to identify and map the distribution of non-native plant species that were of concern to park resource managers or were known to be potentially invasive in other areas. The survey at GRKO was part of a larger inventory and mapping project initiated by the Intermountain Region (IMR) of the National Park Service (NPS). Several cooperators mapped 19 national parks in the Intermountain Region of the western US. The goals of the IMR project were to develop a database that would assist resource managers with invasive plant management and control, provide baseline data for long term monitoring efforts, and facilitate data sharing within the NPS and with external agencies. The specific goals of resource managers at Grant-Kohrs Ranch were: • to develop maps of non-native plant species to assist with non-native plant management and restoration, • to prioritize mapping in habitats with increased risk of invasion, particularly the upland ranges and the Clark Fork River riparian area, • to search for potential new invaders. To achieve these goals we surveyed the area of interest using three different sampling methods. In general, we demarked the area of primary interest with transects. These transects were walked and the occurrence of target non-native plants and other variables were recorded with Global Positioning System (GPS) receivers. In areas of secondary interest, or areas that were too topographically difficult to sample intensively we still used transects but targeted them to follow the landscape or geographical features. Therefore, this approach was biased, providing information around a certain feature but not at a distance from that feature. However, in combination with our primary method we are confident our survey provides representative data of the species occurrence in the environment. The third method was used on areas of least interest to the park or for non-native plants that were present in high density throughout the survey unit (i.e. Canada thistle (Cirsium arvense) in the riparian area) and therefore difficult to delineate accurately into distinct populations. In these situations, we sampled an area either by one of the two methods described above or by visually scanning the survey unit. This “gross area” sampling method was meant to provide only a general assessment of occurrence. Maps of target plant species’ distributions are provided in the report, as well as tables summarizing the acres infested by each species mapped. No sampling method is completely accurate and we therefore provide an estimation of the uncertainty associated with sampling each species. The invasive plant database and maps produced from the survey of Grant-Kohrs Ranch are a singular look at the invasive plant distribution in the spring/early summer of 2003. The data should be considered baseline, or a starting point from which to monitor and assess changes in invasive plant populations in the area over time. A short discussion of the next phase, monitoring invasive plant populations, is included in the conclusion.

Non-Native Plant Survey at Grant-Kohrs Ranch National Historic Site

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