Restoring conifers by natural regeneration on slopes exposed during highway reconstruction, Glacier National Park, Montana, USA

Abstract

In 1991, about 70 years after construction, the 16-km Lake McDonald section of the Going-to-the-Sun Road in Glacier National Park was rebuilt. The road, which is at the base of steep north-west-facing slopes, follows the 975 m contour above Lake McDonald within forests originating after wildfires. Tree composition is mostly western red cedar (Thuja plicata Don ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) with a minor component of six other conifer species. Trees were expected to disperse enough seeds to naturally regenerate road cuts on four land-types with developed soils, but not on the fifth land-type with rock and scree. From 1987 to 1995, red cedar and hemlock dispersed 4466 potentially viable (filled) seeds m-2 on cut slopes while other species added 74 filled seeds m-2. From 1991 to 1995, after reconstruction, an average of 3294 filled red cedar seeds fell m-2, in addition to 511 western hemlock m-2 and 61 m-2 for six other species. On cut slopes from 1992 to 1998, of land-types with developed soils, seeds germinated after snowmelt, usually from early May until the surface dried. Almost no seeds germinated and no seedlings survived on the rock/scree land-type. Due to the harsh environment on cut slopes, most seedlings died. In spring 1999, red cedar and hemlock seedlings were small and inconspicuous and required an average of 312 and 173 filled seeds for each surviving seedling.