• Fajvan, Mary Ann
  The Graduate School, University of Maine
  

Forest stands of red spruce (Picea rubens Sarg.), eastern hemlock (Tsuga canadensis (L. Carr.), and white pine (Pinus strobus L.) were found to have a multi cohort structure. Partial disturbances from insect outbreaks and harvesting affected stand development by initiating a new cohort of tree and causing a growth response in surviving trees. The shade-tolerant red spruce and eastern hemlock comprised more cohorts than the shade intolerant white pine. Stands displayed a vertically stratified canopy with pine usually being the tallest followed by spruce and hemlock. There was more canopy growing space potentially available beneath a dominant pine crown than beneath a dominant spruce or hemlock crown. Total stem wood volumes of sample plots were more affected by variability in age structure than by the presence or absence of pine. Plots with a representation of two or three cohorts were more productive than plots with a single cohort. Management of pine-hemlock-spruce mixtures should focus on 1) maintaining a dominant pine component 2) establishing pine regeneration and 3) maintaining a multi cohort structure through implementation of the irregular shelterwood method.

In stands of shade tolerant balsam fir (Abies balsamea L. Mill.) and red spruce, dominant and coo dominant red spruce trees showing a history of periods of radial growth suppression produced lower site indices than spruce that had always grown freely. Methods that adjusted or eliminated periods of suppressed growth increased estimates of site index and equated them with the site indices of the freely growing trees. Trees that had experienced competition-iduced periods of reduction in diameter growth may also have experienced reductions in subsequent height growth.