Short- and long-term effects of alternative silvicultural systems on stand development of lowland black spruce forests in northern Minnesota, USA

University of Minnesota M.S. thesis. May 2018. Major: Natural Resources Science and Management. Advisors: Marcella Windmuller-Campione, Matthew Russell. 1 computer file (PDF); vii, 55 pages.The black spruce cover type occupies roughly 10% of Minnesota’s 17.4 million acres of forestland and is an important species both ecologically and economically. Black spruce is typically managed using variations of clearcutting, while the effects of managing with alternative silvicultural methods remains largely understudied. Furthermore, studies in the growth of individual black spruce trees are few in the Lake States region. The Compartment Study on the USDA Forest Service’s Big Falls Experimental Forest was established in 1948 to assess how lowland black spruce stands respond to alternative silvicultural methods. It provides the unique opportunity to study both short-term and long-term effects of varying management techniques. Six silvicultural treatments (clear-cut strips, clear-cut patches, shelterwood, light thinning, individual tree selection, group selection) and a control were treated and measured around 1950, with additional measurements occurring five and ten years post-establishment. Ten-year diameter growth was assessed and found to be significantly affected by treatment, and trends were found in individual tree mortality in varying silvicultural treatments. A mixed effects model predicting diameter growth was adapted from previous work and fit to 10,244 observations. The shelterwood, clear-cut strips, and clear-cut patches treatments were re-measured in 2017 to assess long-term differences by treatment. The shelterwood treatment had greater structural and compositional diversity, resulting in stands with larger trees, fewer trees per hectare, and greater basal area per hectare. The results suggest that using alternative silvicultural methods to traditional clear-cuts in managing Minnesota’s black spruce forests may be applicable in lowland stands, particularly where uneven-aged stands have developed due to limited management or lack of disturbances. This is especially in Minnesota, where 67% of the resource is nearing, currently achieving, or exceeding typical rotation ages. However, alternative treatments must be considered in light of forest health issues, especially the presence of dwarf mistletoe