Browsing by Subject "Coarse woody debris (CWD)"

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    The influence of natural disturbance-based silviculture treatments on northern hardwood forests in Northeastern Minnesota, USA.
    (2010-12) Bolton, Nicholas William
    Natural disturbance-based silviculture (NDBS) has been suggested as an approach for promoting late-successional forest characteristics and maintaining native biodiversity in managed forests. Harvest gaps based on the natural disturbance patterns found in the upper Great Lakes (46 study gaps) were created throughout northern hardwood forests in northeastern Minnesota, USA, during the winters of 2002 and 2003. Gaps were measured 6- and 7-years post-treatment and subsequent analysis of these measurements was used to evaluate the success of these treatments at meeting structural and compositional objectives. Results indicated that these gaps have done little to increase tree diversity, including the recruitment of shade mid-tolerant species; however, the richness of herbaceous understory vegetation has responded positively to larger gap sizes. Herbaceous species increasing in harvest gaps included Actaea spp. L. (baneberry), Botrychium virginianum L. (rattlesnake fern), Mertensia paniculata Aiton (Northern bluebell), Rubus idaeus L. (red raspberry), Sanguinaria canadensis L. (bloodroot) and Cirsium arvense L. (Canada thistle). Results also indicated that subtle patterns were found among species spatial establishment within gaps (e.g., gap edge and gap center) and species that expressed no preference between the intact forest and harvest gaps. Levels of downed coarse woody debris (CWD) differed among gap size and all gaps had lower levels of CWD compared to the surrounding intact forest. Due to the historical importance of Betula alleghaniensis in these systems, the factors affecting the recruitment of this species were also investigated. Based on these investigations, it was found that B. alleghaniensis establishment was strongly related to highly decayed, large coniferous pieces of CWD with little recruitment occurring on the undisturbed forest floor. As such, providing appropriate seedbed conditions for shade mid-tolerant species and utilizing natural canopy gap sizes would improve the success of maintaining this species on the landscape.
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    Initial effects of structural complexity restoration treatments and deer browsing on ground-layer community composition and tree regeneration in northern hardwood forests
    (2014-03) Reuling, Laura F.
    As researchers realize the value of old-growth forests and their unique attributes and dynamics, managers have begun developing management regimes aimed at restoring old-growth characteristics in forests managed for wood products. However, changes in these forests since European settlement, especially increased population of white-tailed deer (Odocoileus virginianus Zimmerman) may have important implications for forest composition and regeneration. The objective of this research was to determine the initial (three- and four-year) effects of several old-growth structural restoration treatments and browsing by white-tailed deer on tree regeneration and understory community composition in northern hardwood forests in northern Wisconsin, USA. Community composition and tree regeneration were measured in stands with six different silvicultural treatments replicated across three large study areas (> 50 ha). Treatments consisted of a combination of two levels of coarse woody debris and three overstory gap treatments designed to emulate patterns of natural gap and mesoscale canopy disturbance: small gaps (10.7m diameter), large gaps (18.3 and 24.4m diameter), and a mesoscale wind disturbance treatment consisting of 0.4 and 1.2 ha shelterwoods. All treatments included multiple small deer exclosures to examine the impact of deer herbivory. Assessment of cover by herbaceous plants and seedlings indicated that overstory treatments had a larger effect on understory community composition than browsing by deer, whereas there was no effect of coarse wood levels. Species richness was highest in the small gap treatment and lowest in the control stands, possibly reflecting the increased dominance by a few ruderal and exotic species in treatments with increased canopy openness. Richness was also significantly lower inside exclosures than outside in some treatments, although browse-sensitive Trillium spp. were largely restricted to exclosures. Post-harvest seedling density increased with increasing overstory removal, with the mesoscale wind disturbance treatment containing the highest seedling density after three years. While browse protection generally did not have a significant effect on overall density of regeneration, several species, especially Betula alleghaniensis benefited from protection from deer browse. These initial results underscore the utility of natural disturbance-based treatments at increasing the complexity of second-growth communities and the importance of accounting for herbivory impacts on treatment responses.