Effects of elk and white-tailed deer browsing on Aspen communities and wildlife habitat quality in northern lower Michigan: An 18-year evaluation

Elk (Cervus elaphus nelsoni) and white-tailed deer ( Odocoileus virginianus) browsing in regenerating aspen ( Populus spp.) clearcuts may impact the composition and structure of aspen communities, potentially influencing the production of timber, the quality of habitat for wildlife species, and the abundance of threatened/endangered herbaceous plant species. This study used replicated exclosures (i.e., that had been established in clearcuts for up to 18 years) and paired browsing areas (n = 36) to quantify ungulate browsing effects in bigtooth (Populus grandidentata) and quaking aspen (P. tremuloides ) communities in the Pigeon River Country State Forest (PRCSF), Michigan in 1996--98. Habitat Suitability Index (HSI) models were used to quantify browsing effects on aspen habitat quality for ruffed grouse (Bonasa umbellus) and songbirds.; Ungulate browsing in 1--3 year-old clearcuts was greater in bigtooth than in quaking aspen clearcuts, and browsing decreased as clearcuts aged. Browsing was greater in aspen clearcuts near swamp conifer stands and in landscapes with ≥3 other 1--3 year-old aspen clearcuts. Browsing reduced the density of aspen in bigtooth and quaking aspen clearcuts >13-years-old and caused a 50% reduction in the merchantable volume in 15--17 year-old clearcuts. There were few significant differences in vertical cover, horizontal cover, and the densities of shade tolerant and shade intolerant (excluding aspen) woody species 16--18 years after clearcutting and after being excluded from browsing. Browsing primarily influenced herbaceous communities in quaking aspen clearcuts, resulting in greater frequencies of species indicative of relatively less mature stands. Ungulate browsing decreased ruffed grouse habitat quality in aspen clearcuts by reducing woody stem densities below levels that are the most suitable for ruffed grouse. However, ovenbird ( Seiurus aurocapillus) habitat quality was greater in quaking aspen browsed areas than in exclosures due to reductions in cover <0.5 m in height and understory woody stem density. Bigtooth and quaking aspen stands provided different structural components (both inherently and due to browsing), and had different bird communities. Likewise, aspen clearcuts browsed ≤50% had different songbird species composition than aspen clearcuts browsed >50%. Ruffed grouse and white-throated sparrows were more abundant in areas browsed ≤50%.; Bigtooth and quaking aspen stands provided unique habitat conditions for numerous wildlife and herbaceous species. Furthermore, the reduction of merchantable timber volume was significantly greater in quaking aspen stands. The significant differences in the composition and structure of bigtooth and quaking aspen stands merit distinguishing between the 2 aspen species for timber and wildlife management planning in the PRCSF. Reducing browsing on clearcuts where merchantable timber is desirable may be achieved by increasing clearcut size, evenly distributing clearcuts, providing alternate high quality winter and spring food resources, and altering elk hunting access. The effects of ungulate use on aspen stands should be considered when setting habitat and population management goals to maintain multiple use benefits within the PRCSF. Further monitoring is warranted to determine the potential long-term (∼40 years) ecological and economic impacts browsing may have in aspen clearcuts during a complete harvest rotation.