Genetic impacts of patch cut, shelterwood cut and green tree retention were evaluated in western hemlock (Tsuga heterophylla) and amabilis fir (Abies amabilis) in coastal montane forest using allozyme markers ( El-Kassaby et al., 2003). No significant impacts of silvicultural treatments on genetic diversity of amabilis fir were detected, whereas the shelterwood system resulted in lower heterozygosity in western hemlock. Selection and diameter limit cuts also changed the genetic structure in eastern hemlock (Tsuga canadensis) ( Hawley et al., 2005). Most of the studies on genetic impacts of forest harvesting and renewal practices
are based on existing operational harvesting treatments, as controlled experimental harvesting
and regeneration Selleckchem BEZ235 CB-839 manufacturer experiments are long-term and very expensive. There are three such experiments reported so far in North America; of these EMEND (Ecosystem Management Emulating Natural Disturbance) is the most comprehensive, large-scale and elegant (EMEND, 2014). At the EMEND project site, genetic diversity, inbreeding levels, and population genetic structure of white spruce in conifer-dominated and mixedwood forest, were similar between unharvested control or preharvest old-growth and post-harvest natural regeneration after five harvesting treatments (green tree retention of 75%, 50%, 20%, and 10%, and clearcut), with clearcut showing no negative genetic impacts (Fageria and Rajora, 2013). Adams et al. (1998) examined the effects of shelterwood, group selection and clearcut harvesting in Douglas-fir in a replicated experiment. There was no negative impact of any of the three management systems and natural and artificial
regeneration on overall genetic diversity. However, rare alleles were lost after harvesting in the shelterwood system. El-Kassaby et al. (2003) conducted their study as a part of the partially replicated MASS (Montane Alternative Silvicultural Systems) project involving shelterwood, patch-cut, and clearcut harvesting systems. As already noted above (Section 2.1.2) these silvicultural treatments did not show any negative impact on the genetic diversity of amabilis fir, but medroxyprogesterone heterozygosity was reduced in western hemlock following the shelterwood system. Very little information is available on the impacts of commercial thinning on the genetic diversity of North American forest trees. Although genetic diversity was not significantly reduced after commercial thinning in two Douglas-fir plantations in British Columbia, there were losses of 1–7 alleles after thinning in Douglas-fir and the associated species western hemlock, western red cedar (Thuja plicata), western white pine (Pinus monticola) and Pacific silver-fir (A. amabilis) ( El-Kassaby and Benowicz, 2000). No negative impacts of pre-commercial thinning were observed in fire-origin and harvest-origin stands of lodgepole pine ( Macdonald et al., 2001).