Boreal mixedwood forests: linking early performance of white spruce with future yield
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Presentation given at the 2006 Post-Harvest Stand Development Conference on stock, growth and mortality for white spruce in mixedwood stands.Cite
Understory
Abies balsamea
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A large component of the boreal mixedwood forest is comprised of aspen and white spruce mixtures of varying proportions and ages. The slower growing white spruce usually starts as an understory component but will succeed to a white sprucedominated stand after aspen break-up. Since both species are utilized by the forest industry, one method of maximizing total yield is to protect the unmerchantable white spruce understory while harvesting the merchantable aspen overstory. Although some of the white spruce understory is lost when the machine corridors are harvested, future conifer yield is augmented by the accelerated growth of the protected spruce component, a result of increased light levels. In a 10 year trial comparing the growth of released versus control understory spruce, annual height growth, diameter growth and volume increment were 76%, 152% and 83% higher, respectively, for the released conifer compared to the control. In order to account for the yield implications in timber supply analysis, accurate forecasts of future stand development can only be obtained through the use of a forest growth model since long-term data are not available. The Mixedwood Growth Model (MGM) has a unique architecture that allows for the modeling of various strata in understory protection stands. This “multi-strata” modeling approach was used to forecast the combined yield of all the strata, including the impact of adjacent strata with regards to light availability. Operational examples of understory protection, data on white spruce release and aspen regeneration, as well as modeled volume forecasts are presented.
Understory
Silviculture
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Natural regeneration
White (mutation)
Silviculture
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Scarification
Natural regeneration
White (mutation)
Natural forest
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Clearcutting
Abies balsamea
Silviculture
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Over the past two decades, partial harvesting has been increasingly used in boreal forests as an alternative to clearcutting to promote irregular stand structures and maintain a balance between biodiversity preservation and continued timber production. However, relatively little is still known about the silvicultural potential of partial harvesting in Canada’s boreal forest, especially in areas prone to organic matter accumulation (paludification), and most prior research has focused on biodiversity responses. In this study, we assess the effects of partial harvesting on stand development (recruitment, growth, and mortality) ten years after harvesting in previously unmanaged black spruce stands and quantify its effectiveness in reducing the impacts on ecosystem structures. Our analyses revealed that pre-harvest stand structure and site characteristics, especially initial basal area, sapling density, tree diameter, and organic layer thickness (OLT) were major factors involved in stand development ten years following these partial harvesting treatments. Depending on pre-harvest structure and site characteristics, partial harvesting can result in either an increase in post-harvest tree recruitment and growth or a loss of stand volume because of standing tree mortality. To increase the chances of partial harvesting success in ensuring an increase in decennial stand yield after harvest in black spruce forest stands, sites prone to paludification (i.e., where OLT >17 cm) should be left unharvested. This study illustrates the importance of taking into account pre-existing structure and site characteristics in the selection of management strategies to maximize the potential of partial harvesting to achieve sustainable forest management in black spruce stands.
Basal area
Clearcutting
Black spruce
Sustainable Forest Management
Silviculture
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Windthrow
Basal area
Silviculture
Clearcutting
Natural regeneration
Understory
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Girdling
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The Hotchkiss River Mixedwood Timber Harvesting Study developed new approaches to harvesting systems for western Canada's boreal mixedwood forests. Conventional harvesting equipment was used to test 11 harvesting and silvicultural systems over a 530-ha site. These include one- and two-pass modified uniform shelterwoods, two- and three-pass strip shelterwoods, two-pass alternate strip shelterwoods and four-pass progressive strip shelterwoods. These were used to test varying levels of wind protection designed to protect and minimize wind damage to understorey (immature) white spruce residuals following harvest of the aspen overstorey. Ongoing monitoring of wind dynamics and associated windthrow patterns since 1992 have provided clear management practice guidelines for reducing windthrow of immature spruce and residual aspen following harvesting. There are thresholds related to spruce height and distance from aspen residuals, beyond which windthrow damage increases significantly. The influence of topography, timing of harvest and the spatial configurations of multiple harvests on windthrow dynamics have been clarified through this research. These results have provided valuable information to help forest planners to utilize harvesting and silvicultural systems that best reduce windthrow damage to understorey spruce, following harvest of overstorey aspen.
Windthrow
Understory
Silviculture
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The effects of partial cutting on species composition, stand structure and growth, tree size distribution, and tree disease and mortality were evaluated on 73 plots in 18 stands that were harvested 12–96 years ago in southeast Alaska. Partially‐cut stands had diverse and highly complex stand structures similar to uncut stands. Sitka spruce was maintained in mixed hemlock–spruce stands over a wide range of cutting intensities. Analysis of the data did not detect significant changes in tree species composition, stand growth, hemlock dwarf mistletoe infection and incidence of tree wounding or mortality rates with partial cuts. Silvicultural systems using partial cutting could provide a sustainable timber resource including more valuable spruce trees, while also maintaining stand structural diversity and old‐growth characteristics.
Western Hemlock
Clearcutting
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Citations (28)