Prolonged herbicide-induced vegetation changes in a regenerating boreal aspen clearcut

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.02.017 Byline: W.L. Strong (a), S.S. Sidhu (b) Abstract: A soil-active herbicide (hexazinone) was applied (0, 2, and 4kg/ha of active ingredient) in a 3-year-old regenerating boreal Populus tremuloides Michx. (aspen) clearcut to determine its effect on the compositional and structural development of the vegetation. Woody stem densities and plant foliar cover were evaluated prior to and 2, 6, and 17 years after treatment. Herbicide treatment at the 2 and 4kg/ha rates reduced tree and total woody stem densities relative to the 0kg/ha level. The 4kg/ha level reduced stem densities by 27% 17 years after treatment. The primary reductions occurred in Amelanchier alnifolia (Nutt.) Nutt. ex M. Roemer (saskatoon) and Rosa acicularis Lindl. (wild rose); whereas Corylus cornuta Marsh. (beaked hazelnut) and Viburnum edule (Michx.) Raf. (low-bush cranberry) stem densities increased. Notable herbicide-caused foliar cover reductions at the 4kg/ha level occurred in Eurybia conspicua (Lindl.) Nesom. (showy aster), Mertensia paniculata (Ait.) G. Don. (tall mertensia), Rubus pubescens Raf. (dewberry), and Spiraea betulifolia Pallas (spiraea), but Aralia nudicaulis L. (sarsaparilla), Cornus canadensis L. (bunchberry), and Symphyotrichum ciliolatum (Lindl.) A.&D. Lve (Lindley's aster) increased. Less distinctive but similar changes occurred in the 2kg/ha treatment. Total plant cover, species richness, and species dominance concentration were similar among treatments. Eight distinctive forest understory-types were recognized among treatments in Year 17. Between the 0 and 4kg/ha treatments, five understory-types differed in their frequency of occurrence. Hexazinone did not improve the survival of silviculturally planted Picea glauca (Moench) Voss (white spruce) seedlings relative to untreated sites, but the 4kg/ha treatment level did increase Pinus contorta Dougl. ex Loud. (lodgepole pine) survival from 12 to 34%. Surviving seedlings had significantly greater height and basal diameter growth than those at the 0kg/ha sites, particularly the 4kg/ha treatment. Author Affiliation: (a) Faculty of Environmental Design, University of Calgary, 2500 University Drive N.W., Calgary, Alta., Canada T2N 1N4 (b) (Retired) Canadian Forest Service, 5320-122 Street, Edmonton, Alta., Canada T6H 3S5 Article History: Received 1 May 2004; Revised 23 September 2004; Accepted 28 February 2005