A Survey of Non-indigenous Plant Species in the Northern Range ofYellowstone National Park, 2001-2004. Final Report.

Rew, Lisa; Maxwell, Bruce; Dougher, Frank; Aspinall, Richard; Weaver, Tad; Despain, Don

(Abstract incomplete, see original document) An inventory/survey of the occurrence and location of non-indigenous plant species (NIS) is seen as the first of three phases in their management. A survey needs to be designed to obtain an unbiased assessment of NIS extent over the whole area of interest. Data from the inventory or survey can then be used as baseline data to select patches (populations) for monitoring. Monitoring methods should aim to evaluate changes in spatial and temporal extent of NIS, impacts of NIS on the ecosystem, and impacts of management on NIS and surrounding ecosystem. The survey data when developed into probability of occurrence maps can also be used to strategically survey for new populations. Only after following these steps to estimate NIS plant occurrence, extent, dynamics and impacts, can effective management strategies be developed for the currently occurring species as well as new species, that may invade National Parks and other wilderness/natural areas. The overall aim of this project (2001-2004) has been to survey the occurrence (presence/absence) of NIS within the northern elk winter range of YELL. Covering an area of 152,785 ha, the northern range is too large to look for NIS species over its entirety. In 2001, we focused on identifying which sampling methods provide the most representative sample of species occurrence in the landscape. This objective was achieved through computer simulation and field sampling. As a result we adopted a stratified-random sampling methodology that would maximize our ability to predict occurrence of the NIS. In field seasons 2001 through 2003, our crews sampled 295 transects in the area between Gardiner on the west and Silvergate on the east and from the northern boundary of YELL to as far south as Tower Falls. Sixty-three NIS are on the YELL target list. Over the four year study we have observed and recorded 29 of them. Only nine of the observed NIS occurred on more than 1% of the surveyed area (in descending order of occurrence): Phleum pratense, Poa pratensis, Bromus tectorum, Cirsium arvense, Bromus inermis, Alyssum desertorum, Linaria dalmatica, Elymus repens and Cardaria chalepensis. Maps of where these nine species were located on our transects are provided in this report. While such maps are useful they do not provide any information on areas which were not surveyed. Therefore, the 2001-2003 NIS data were analyzed for correlations with human disturbances (roads and trails) and environmental variables to aid in the prediction of NIS occurrence in areas not sampled. Thus, we have generated maps of probability of occurrence for the nine most frequent species, which are also in this report. The probability of occurrence maps provide insight as to where a particular NIS is most likely to be, based on correlations with variables in the model. However, the species may not be there yet, which makes model evaluation difficult. In 2004, we stratified our sampling transects based upon the results of our probability maps to validate the predictive model results. The results all showed the correct trend, i.e. the target NIS was found increasingly more often as the predicted occurrence also increased. However, the model tended to predict a higher percentage occurrence than we observed in the field. As one would expect some models and observations agreed more (e.g. Phleum pretense and Bromus tectorum) than others (e.g. Bromus inermis). Statistical analysis of the model predictions suggested the model fits were good. The fact we observed less NIS in the field than the model predicted, may suggest that the species has not arrived or reached its full potential in the environment yet. We feel that it may be better to over predict then under-predict when the purpose of the study was to identify all locations of each species. (Abstract as submitted by authors although incomplete, please see original document).

A Survey of Non-indigenous Plant Species in the Northern Range ofYellowstone National Park, 2001-2004. Final Report.

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