Aspen-Dominated Forest Response to Harvest Residue Removal and Compaction Varies with Site Conditions.

Global change and associated threats to forest productivity and function have increased the breadth of potential forest management objectives.  For example, residues from conventional harvests are increasingly being thought of as a potential source of bioenergy feedstocks.  In the Lake States region, aspen-dominated forests are often assumed to be resilient to harvesting and other disturbance, but there remains some uncertainty about how productivity, stand development, species composition, and function might be impacted over the long-term by increased biomass removal. We used data from Long-Term Soil Productivity study installations at the Chippewa, Ottawa, and Huron National Forests to address the following questions: 1) Does whole-tree harvest (removing residues) decrease standing biomass in aspen-dominated forests over time? 2) Does whole-tree harvest influence the species composition, biodiversity, and function of the regenerating forest? 3) Do responses vary across differences in soil texture and site quality?

Harvest treatments had different effects on standing biomass over time at the different sites.  On sandy soils whole-tree harvest reduced mean tree standing biomass at 15 years by 25% compared with conventional, stem-only harvest.  Increased compaction of sandy soils did not have a negative effect on standing biomass and neither residue removal nor compaction influenced community composition.  In contrast, there was no evidence of a negative impact on standing biomass 15 years after whole-tree harvest on clayey or silty loam soils, but increased compaction reduced standing biomass, particularly of tree species.  Measures of functional diversity based on species abundance and plant traits also varied in response to treatments across sites, and closer examination revealed that those responses may be more reflective of the abundance of aspen following disturbance than of direct impacts from disturbance severity.