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An Assessment of Exotic Plant Species of Rocky Mountain National Park


Objective 1: Identify Exotic Species

A list of known exotic species was initially prepared by park personnel. This list was compiled using the Romoflora database, herbaria records, the Catalogue of the Vascular Plants of Rocky Mountain National Park (Weber 1988), park research reports (Rocky Mountain National Park Resource Management Reports #1 and #13), and field surveys by the Denver Botanical Gardens (Yeasts, 1987, 1988, 1990, 1991). Species considered to be non-native to North America, native to North America but introduced into RMNP, or native to North America but not known to be native to RMNP, were all included on the list. Adventive (occasional occurrence, though not thoroughly naturalized), naturalized (well adapted and growing in region where plant is not native), cosmopolitan (having nearly worldwide distribution), cultivated (grown as a crop or ornamental), and escaped (formerly cultivated) species were considered to be exotic (Stubbendieck 1994). In addition, attempts were made to include exotic species that currently are not present in RMNP, but can be found near park borders.

Objective 2: Rank Exotic Plant Species of RMNP

One of the objectives for this project was to assess the potential ecological impacts for the known exotic plant species of RMNP. To accomplish this objective, all species on the list of known exotic plants for RMNP were evaluated. A literature review was conducted to collect information on the basic life history traits for each species. The literature review primarily focused on obtaining information necessary for the Screening Assessment portion of the Ranking System (Appendix II). General reference sources along with specific journal articles were used to construct a database for all exotic species. Appendix III contains a list of general references that were particularly useful sources of information. In some cases, little information was available on the life history characteristics. In these cases, information on species of the same genera or family was collected.

Once information was obtained from the literature review, the species were ranked according to the Screening Assessment portion of the Ranking System for RMNP (Appendix II). Species were assigned scores for each category of the Screening Assessment. Attempts were made to use conservative estimates for the scores assigned to each category, especially for areas where information was limited.

All species then received a total score for potential distribution and potential ecological impact. An important note is that all rankings for potential distribution and potential ecological impact are relative scores. The scores only represent the potential distribution and potential ecological impacts of each species relative to other species using life history information. These scores should only be used to make comparisons between species, and have little meaning outside of this context.

The scores for all species were compared to assess their overall potential ecological impact. Species that received a total potential ecological impact score equal to or greater than 24 (60 % of the total points possible) were identified as 'species of concern'. Species which received scores below 24 were believed to have a relatively low overall potential ecological impact, and no additional information was collected for these species. However, information from the initial literature review for species not believed to be potential problems is included Literature Review for Remaining Exotic Species section.

Additional information from a more thorough literature review was then collected for all species of concern. The second literature review concentrated on obtaining additional information on life history characteristics as well as management options for each species of concern. The species were then ranked again, using the Final Assessment section of the Ranking System for RMNP (Appendix II). Species that currently have a limited distribution in RMNP, but have a high potential distribution and a high potential ecological impact were identified as a 'high' priority for management. Species with large current distributions, or species that are relatively easy to control were identified as 'medium" priority for management.

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