Forest Genetic Resources Training Guide Forest Management Does selective logging degrade the genetic quality of succeeding generations through dysgenic selection? Jonathan Cornelius

Forest Genetic Resources Training Guide La Mosquitia, Honduras

Forest Genetic Resources Training Guide “Mahogany bush” “Mahogany bush--a dark mass of vegetation appearing without prelude on the savannas”

Forest Genetic Resources Training Guide “The woods are coming to life again”

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)

Forest Genetic Resources Training Guide Iquitos, Peruvian Amazon

Forest Genetic Resources Training Guide Medicinal species, Iquitos

Forest Genetic Resources Training Guide Fruit species

Forest Genetic Resources Training Guide The aguaje palm (Mauritia flexuosa)

Forest Genetic Resources Training Guide A major local industry

Forest Genetic Resources Training Guide Harvesting aguaje

Forest Genetic Resources Training Guide Mauritia flexuosa types

Forest Genetic Resources Training Guide

Dysgenic selection Dysgenic selection is selection that leads to an undesirable directional change in genetic quality over one or more generations

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)

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)

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)

Forest Genetic Resources Training Guide What is selective logging?

Forest Genetic Resources Training Guide Within-species selective logging

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)

Forest Genetic Resources Training Guide Positive phenotypic selection aiming at genetic improvement best trees selected

Forest Genetic Resources Training Guide Negative phenotypic selection, possibly leading to dysgenic selection worst trees selected

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

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 )

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

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

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

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

Forest Genetic Resources Training Guide Mahogany logging in Brazil

Forest Genetic Resources Training Guide Marajoara before logging

Forest Genetic Resources Training Guide Marajoara before logging Marajoara after logging based on Grogan et al. 2008

Forest Genetic Resources Training Guide “Mahogany bush” “Mahogany bush--a dark mass of vegetation appearing without prelude on the savannas”