Element 4 : Hardwood initiative - Development of new processes and technologies in the hardwood industry (Project 17) - Impact of partial harvesting on tree grade: projections for northern hardwoods of the Acadian Forest Region
The objective of commercial thinning and partial harvesting has traditionally been to improve and increase the amount of higher quality stems for sawlog and veneer products, reduce losses from mortality, and reduce the harvest rotations for even-aged silvicultural systems. Literature on the impact of partial harvesting on stand dynamics, tree grade changes, fibre attributes, and potential forest products to promote uneven-aged and structures and management is scare for the northern hardwood forests of the Acadian Forest Region. A long-term selection harvest study established in west-central New Brunswick provides the opportunity to obtain such information under the FPInnovations and Natural Resources Canada, Canadian Wood Fibre Centre Eastern Hardwood Research Initiative. Results from the study suggest that the treated stands did benefit in the terms of growth and improved quality, but stand restoration is a slow process in the second growth uneven-aged stands on a 20-year harvest cycles. Stand growth responses and tree grade changes for both the control and treated plots are within the values reported for northern hardwood stands and are influenced by a number of treatment and biological factors.
The results of fifteen years of observation are discussed in the context of the major publications existing in the literature for stand dynamics, tree grade changes, and the occurrence of ingrowth. In summary, greater is the basal area removal, the greater the diameter response of individual residual trees in the thinned plots. The thinned stands have not recovered the basal area values that existed at the initiation of this study Annual volume increment growth rates suggest that hardwood stands subjected to partial removals produced better growth response than was predicted at the start of the original study. Stand restoration and stem quality improvement are slow processes that may not be achieved with a first harvest entry in second-growth northern hardwood stands that have had the higher quality trees removed repeatedly in the past. Changes in tree grades were observed to be very dynamic in these second-growth northern hardwood stands because of a number of factors such as initial stem quality, stem growth, mortality rates, harvest rates (both regulated and unregulated), species, and site quality. As expected, ingrowth occurred more frequently in the thinned stands than the control stands. Except for one study site with more “mixedwood” characteristics ingrowth does not exist as a diverse mixture of desired tree species but a secondary canopy of dense American beech and sugar maple.