Canadian Forest Service Publications
Impact of partial harvesting on stand dynamics and tree grades for northern hardwood trees of the Acadian forest region. 2013. Swift, D.E.; Duchesne, I.; Ung, C.-H.; Wang, X.; Gagné, R. Information Report FI-X-009E. NRCan, CFS-CWFC, Fredericton, NB.
Issued by: Atlantic Forestry Centre
Catalog ID: 34981
Series: Information Report (CWFC - CFS)
Availability: PDF (download)
The objectives of commercial thinning and partial harvesting have traditionally been to improve and increase the amount of higher quality stems for sawlog and veneer products, reduce losses from mortality, and reduce 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 stand structures and management is scarce for the northern hardwood forests of the Acadian Forest Region. A long-term selection harvest study established in west-central New Brunswick provides an opportunity to obtain such information under the Eastern Hardwood Research Initiative of FPInnovations and Natural Resources Canada, Canadian Wood Fibre Centre. Results from the study suggest that the treated stands benefited in terms of growth and improved quality, but stand restoration is a slow process in second-growth, uneven-aged stands on 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 15 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, the greater the basal area removed, 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 start 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 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 repeatedly had the higher quality trees removed 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 in the control stands. Except for one study site, which featured a more “mixedwood” characteristic, ingrowth did not exist as a diverse mixture of desired tree species but as a secondary canopy of American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.).
Plain Language Summary
We don’t know enough about how partial harvesting (thinning) affects stand growth or the external appearance of northern hardwood trees in the Acadian Forest Region in New Brunswick. This information would be helpful for sustainable management of the resource. Five of the oldest stands in the region were studied: each study site contained two plots, one in an area where the trees were not cut (control) and another where the trees were thinned. Results show variable stand conditions and removal rates produced variable growth responses, consistent with our review of the literature. Past predicted annual volume increment growth rates of 2.4 m3/ha /year were verified for the control stands. Stand restoration and stem quality improvement are slow processes that may not be achieved after a first harvest entry in second-growth northern hardwood stands in which higher quality trees have been repeatedly removed in the past.