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Forest Genetic Resources Training Guide Forest Management Does selective logging degrade the genetic quality of succeeding generations through dysgenic selection? Jonathan Cornelius
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Forest Genetic Resources Training Guide La Mosquitia, Honduras
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Forest Genetic Resources Training Guide “Mahogany bush” “Mahogany bush--a dark mass of vegetation appearing without prelude on the savannas”
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Forest Genetic Resources Training Guide “The woods are coming to life again”
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Forest Genetic Resources Training Guide Regeneration assured? “…more than 40 per cent of the trees are infested with a termite, the Coptotermes crassus, which penetrates to the heart of the tree…as the government taxes the mahogany concessionaires twelve dollars for each cut tree…care is taken to allow the termite-infested trees to stand…so that a method of natural reforestation is thus ensured—not by man but in spite of him” (Von Hagen 1940)
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Forest Genetic Resources Training Guide Iquitos, Peruvian Amazon
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Forest Genetic Resources Training Guide Medicinal species, Iquitos
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Forest Genetic Resources Training Guide Fruit species
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Forest Genetic Resources Training Guide The aguaje palm (Mauritia flexuosa)
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Forest Genetic Resources Training Guide A major local industry
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Forest Genetic Resources Training Guide Harvesting aguaje
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Forest Genetic Resources Training Guide Mauritia flexuosa types
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Forest Genetic Resources Training Guide
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Dysgenic selection Dysgenic selection is selection that leads to an undesirable directional change in genetic quality over one or more generations
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Forest Genetic Resources Training Guide Claims of dysgenic selection and variation patterns “...another noteworthy feature is the lack of distinct variation patterns in relation to latitude and longitude; this may be due to the fact that the natural forests around the Mediterranean have been disrupted by man and subject for centuries to dysgenic selection” (Palmberg 1975)
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Forest Genetic Resources Training Guide Claims of dysgenic selection and selective logging “...in most areas this once famous tree now occurs as little more than a much-branched bush or small tree, a prime example of extreme genetic erosion due to past over exploitation of the best genotypes” (Pennington et al. 1981)
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Forest Genetic Resources Training Guide Claims of dysgenic selection and selective logging “...selective logging may promote dysgenic selection as a result of the continuous exploitation of large, superior individuals” (Lemes et al. 2007)
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Forest Genetic Resources Training Guide What is selective logging?
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Forest Genetic Resources Training Guide Within-species selective logging
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Forest Genetic Resources Training Guide Dysgenic selection: the mirror image of genetic improvement Distribution of dbh in a commercial plantation of Vochysia guatemalensis (Sarapiquí, Costa Rica)
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Forest Genetic Resources Training Guide Positive phenotypic selection aiming at genetic improvement best trees selected
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Forest Genetic Resources Training Guide Negative phenotypic selection, possibly leading to dysgenic selection worst trees selected
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Forest Genetic Resources Training Guide There are no documented examples of dysgenic selection in forest trees Poor form and slow growth are common, but can be caused by many factors
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Forest Genetic Resources Training Guide The breeders’ equation …allows us to predict the effect of phenotypic selection, whether positive (improvement) or negative (dysgenic) Response to selection (R) = selection differential (S) x heritability (h 2 )
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Forest Genetic Resources Training Guide The breeders’ equation: Response to selection (R) = selection differential (S) x heritability (h 2 ) For example, if trees grown from improved seed grow 10% more quickly than those grown from unimproved seed, then the response to selection is 10% Response to selection = the improvement or decline in performance for a given characteristic from one generation to the next
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Forest Genetic Resources Training Guide The breeders’ equation: Response to selection (R) = selection differential (S) x heritability (h 2 ) Selection differential is a within-generation measure of phenotypic superiority and will usually reflect environmental differences as well as genetic differences Selection differential = the difference between the mean of the selected individuals and the mean of the population If plus-tree mean dbh is 40 cm and population mean dbh is 20 cm, then S = 20 cm
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Forest Genetic Resources Training Guide The breeders’ equation: Response to selection (R) = selection differential (S) x heritability (h 2 ) The value of heritability varies from zero to one Heritability = the degree to which the superiority measured in the selection differential is passed on to the progeny of the selected individuals
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Forest Genetic Resources Training Guide The breeders’ equation: Response to selection (R) = selection differential (S) x heritability (h 2 ) R = Sh 2 = 20 cm x 0.2 = 4 cm
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Forest Genetic Resources Training Guide Mahogany logging in Brazil
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Forest Genetic Resources Training Guide Marajoara before logging
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Forest Genetic Resources Training Guide Marajoara before logging Marajoara after logging based on Grogan et al. 2008
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Forest Genetic Resources Training Guide “Mahogany bush” “Mahogany bush--a dark mass of vegetation appearing without prelude on the savannas”
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