Genetic evaluation of alternative silvicultural systems in coastal montane forests: western hemlock and amabilis fir

Abstract

Genetic diversity and mating system were quantified for shelterwood, patch cut and green tree-retention silvicultural systems, and compared to adjacent old-growth. This is a component of a larger study conducted in montane old-growth forests of coastal British Columbia to evaluate the feasibility and ecological consequences of alternative silvicultural systems. The experiment includes replicated treatments representing a range of overstory removal adjacent to old-growth and clearcut areas. Based on 22 electrophoretically assayed loci, the effects of silvicultural systems on genetic parameters of amabilis fir (Abies amabilis and western hemlock (Tsuga heterophylla were assessed by comparing an average number of alleles per locus, the percent polymorphic loci, and observed and expected heterozygosity between parental populations and naturally regenerated progeny as well as among treatments. Genetic variation in natural regeneration was greater than in parental populations, especially for low-frequency alleles. Silvicultural treatments caused no significant differences in amabilis fir genetic-diversity parameters, while the shelterwood system resulted in lower observed and expected heterozygosity in western hemlock. Nei's genetic distance revealed that all parental populations were extremely similar. The two species had contrasting mating system dynamics with amabilis fir producing higher levels of correlated paternity and inbreeding with wider variation among individual tree outcrossing-rate estimates. Western hemlock had significant levels of correlated paternity only for the green tree and shelterwood treatments demonstrating family structuring inversely related to stand density. Inbreeding in western hemlock was significant but lower than that observed for amabilis fir with a J-shaped distribution for individual tree multilocus outcrossing-rate estimates. The pollination and dispersal mechanisms of the two species represent the most-likely factors causing these differences. Artificial regeneration may be utilized to augment the genetic resources of natural ingress.

Pollen movement under alternative silvicultural practices in native populations of Scots pine (Pinus sylvestris L.) in central Spain

“…Sarg. (El-Kassaby et al, 2003) and for Pinus caribaea Morelet (Zheng and Ennos, 1997; but see contrary results in Neale and Adams, 1985;El-Kassaby and Jaquish, 1996). We suggest that the apparent increase of consanguineous matings after cutting found in the present study could be due solely to sampling error (for they are far from significant).…”

“…Most studies have compared genetic diversity of adult stands with that of naturally regenerated recruits, under alternative cutting methods (Neale, 1985;Adams et al, 1998;Rajora, 1999;Thomas et al, 1999;El-Kassaby, 2000;Glaubitz et al, 2000;Perry and Bousquet, 2001;El-Kassaby et al, 2003). Some studies suggest a small loss of low-frequency alleles among residual trees and natural regeneration, subsequent to shelterwood harvesting (Adams et al, 1998), but most studies have failed to find any significant effects of silvicultural practices on genetic diversity measures of regenerated stands.…”

Genetic diversity and differentiation in European beech (Fagus sylvatica L.) stands varying in management history

“…Genetic diversity was decreased in Picea glauca (Rajora, 1999) after artificial regeneration and in Swietenia macrophylla after logging (Gilles et al, 1999). In Tsuga heterophylla the genetic diversity was lower in patch cut and shelterwood stands than in natural stands (El-Kassaby et al, 2003). On the other hand, no significant differences in genetic diversity parameters were found between path cut, shelterwood and natural stands in Abies amabilis (ElKassaby et al, 2003), In Douglas-fir no effect was observed after shelterwood or thinning compared to no-management (Neal, 1985;El-Kassaby and Benowicz, 2000).…”

“…The genetic consequences of forest management receive more attention nowadays, but are still restricted to conifers (Buchert et al, 1997;Rajora, 1999;El-Kassaby et al, 2003;Macdonald et al, 2001;Adams et al, 1998), some tropical species (Gilles et al, 1999;Lee et al, 2002) and the genus Eucalyptus (Glaubitz et al, 2003a,b). However, conflicting results were presented for different species.…”

Evaluating Interior Spruce Seed Deployment with GIS-Based Modeling Using British Columbia’s Prince George Seed Planning Zone as a Model

“…Thus, the diversity of tree species and tree size is a factor of stand establishment that should be considered during regeneration (WANG and CHEN, 2010). In addition, an increased mixture of plantation and natural regeneration areas may serve to increase the genetic diversity of the forests (EL-KASSABY et al, 2003). However, unpredictable factors such as changes in climatic conditions and/or pests need to be assessed when such clusters occur (PARKS and BEMIER, 2010).…”