Questions: Does the increase in disturbance associated with removing harvest residues negatively impact biodiversity and resilience in aspen-dominated forest ecosystems? How do responses of functional diversity measures relate to community recovery and standing biomass?. Location: Aspen (Populus tremuloides, Michx.) mixedwood forests in Minnesota and Michigan, USA. Methods: Three levels for two factors, organic matter removal and compaction, were fully crossed, resulting in nine experimental treatments that spanned a range of disturbance severity. Each treatment was replicated three times at each of three sites dominated by the same tree species but having different soil textures (clay, silty loam, sandy). Community composition and taxonomic diversity (species richness, species evenness, Shannon diversity index) were quantified based on woody species abundance sampled 5, 10 and 15 yr after disturbance. Community composition response was assessed using non-metric multidimensional scaling. Functional diversity (functional richness, evenness, dispersion and divergence) was also estimated using eight species effect and response traits. Finally, we examined community recovery as well as responses of species and functional diversity to disturbance severity over time using repeated measures ANOVA. Results: Two responses indicated a potentially negative impact of whole-tree harvest relative to conventional, stem-only harvest: functional richness on silty loam soils and species evenness on clayey soils. Otherwise, negative impacts were restricted to forest floor removal or increased compaction. Recovery in community composition was reduced by the most severe treatments, particularly forest floor removal, across the study, but the responses of functional and taxonomic diversity varied among sites, with some measures increasing as a result of severe disturbance. Conclusions: Maximization of standing biomass may mean a short-term sacrifice in species and functional diversity. Also, examinations of forest management impacts on species and functional diversity and composition should apply multiple metrics and indices to ensure potential impacts are not obscured by the reliance on a single approach.
Bibliographical noteFunding Information:
The authors thank J. Elioff, D. Kastendick, J. Kragthorpe and many other USDA Forest Service scientists and technicians for their work in starting and maintaining the LTSP study. M. Carson, F. Falzone and S. Graves provided technical assistance. S. Fraver and M. Cornett provided helpful comments. D. Waller and G. Sonnier shared species trait data. Funding was provided by the DOE/USDA Biomass Research and Development Initiative, the USDA Forest Service, Northern Research Station, and a Doctoral Dissertation Fellowship from the University of Minnesota to M. Curzon.
- Bioenergy harvest
- Community composition
- Functional diversity
- Populus tremuloides