2.3. Regulation of forest structure
Age-class forests dominate most intensively managed
areas in the temperate and boreal region. Forest
compartments comprise trees with similar age, and the
rotation cycle decides on the frequency of final cuttings.
Trees reproduce in non-overlapping generations,
limiting options for matings among relatives
to trees of the same generation. Natural regeneration in
age-class forests is often established in a single or a
few years of heavy fruiting (‘‘mast years’’) (Mu¨ller,
1990). Fertility components of trees are known to vary
strongly among years (Mu¨ller-Starck, 1985). Thus, the
limitation of regeneration to one or a few periods of
flowering and seed production is expected to result in a
reduction of reproduction effective population sizes by
discriminating certain trees from participating inbetween the parental trees and their progenies
is favored by a short phase of natural
regeneration. These processes are enhanced if regeneration
is promoted in years of low seed production.
reproduction. Furthermore, non-adaptive genetic differentiation