Recreational portage trails as corridors facilitating non-native plant invasions of the Boundary Waters Canoe Area Wilderness (U.S.A)

Published source details Dickens S.M., Gerhardt F. & Collinge S.K. (2005) Recreational portage trails as corridors facilitating non-native plant invasions of the Boundary Waters Canoe Area Wilderness (U.S.A). Conservation Biology, 19, 1653-1657.
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Summary

Recreational use of wilderness areas may facilitate transport of non-native plant species propagules and create disturbed sites suitable for establishment of such non-native species. The influence of recreational trails on the introduction and establishment of non-native plants into a wilderness area experiencing low levels of human disturbance in Minnesota, U.S.A., was investigated as few studies have examined such less-disturbed locations. Results of previous studies in more disturbed areas suggest that old roads and trails may act as corridors of invasion.

Study area: The relationship between non-native plant invasions and human disturbances associated with recreational portage trails in the Boundary Waters Canoe Area Wilderness (BWCAW) of northern Minnesota (U.S.A.) was investigated. Historically the area experienced numerous natural disturbances, including fire, tree blow downs and wildlife trails. Before wilderness designation in 1978, much of the BWCAW was logged. Most people (numbers limited by a permit system) travel within the BWCAW by canoe, and a system of trails links the many lakes and rivers so that canoeists can travel throughout the area.

The habitat sampled included three main forest types: Great Lakes pine forest dominated by white pine Pinus strobus and red pine Pinus resinosa with paper birch Betula papyrifera and big-toothed aspen Populus grandidentata; Jack pine forest dominated by jack pine Pinus banksiana with P.resinosa, white oak Quercus alba and beaked hazelnut Corylus cornuta; Boreal hardwood-conifer forest dominated by big-toothed aspen, paper birch, balsam fir Abies balsamea, white spruce Picea glauca and northern white pine Thuja occidentalis; and wetlands (including sedge fens, black spruce-Sphagnum bogs and white cedar-black ash swamps).

Vegetation sampling: During June–August 2002, vegetation along 20 portage trails was sampled. Trails were randomly chosen for which permits were available along a gradient of accessibility, four accessible by vehicle and 16 that were not. Trails that were affected by high winds during storms in 1999 were avoided. Three transects were established perpendicular to each trail. The distance of the transect from the start of the trail and the distance from the side of the trail were randomly selected. Along each transect, four 1 m radius circular plots were established 0, 10, 25 and 50 m from the trail edge. In each, non-native plants were identified and their percent cover estimated.

For each trail, the distance from the nearest entry point and trail length were measured. Distance from entry point was measured from the parking area to the start of the trail using the shortest combination of trails and lakes. Habitat was categorised according to the four main habitat types, and habitat variables (percent canopy cover, substrate type, slope and aspect) were measured.

Six non-native plant species were recorded in the 240 plots. These were: common plantain Plantago major (35 plots), red clover Trifolium pratense (9 plots), white clover T.repens ( 7 plots), dandelion Taraxacum officinale (4 plots), orange hawkweed Hieracium aurantiacum (1 plot) and creeping thistle Cirsium arvense (1 plot).

Non-native richness and cover were significantly affected by distance from trail but not related to distance from wilderness entry point. All six of the non-natives were either directly on or within 1 m of trails.

There was no relationship between non-native richness or cover and trail length, percent canopy cover, slope, forest type or aspect. Non-native cover showed a relationship with trail substrate, with cover highest in plots with a sand or gravel substrate.

Conclusions: This study indicates that non-native plants are utilizing recreational trails in the BWCAW as colonization corridors. Non-native plants have dispersed and established along trails but have not invaded areas beyond them. This implies that they are restricted to areas that have or are experiencing human disturbance facilitating invasions by either propagule dispersal or habitat alteration. Tolerance to trampling (e.g. common plantain) may facilitate colonisation, especially where bare ground provides space and decreased competition from native plants.

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