Growth and net assimilation rates in thinned and unthinned stands of balsam fir

Publisher Website
Google Scholar
Abstract
Current annual stem growth rates per hectare of unthinned young stands of balsam fir (Abies balsamea (L.) Mill.) were 2-3 times greater than in adjacent stands thinned 4-6 years earlier, largely because unthinned stands contained 2.5-4.0 times more foliar weight per hectare. Stem growth rates per tree in thinned stands were 3-8 times greater than those in unthinned stands because of the reduced competition and the lower ratio of heterotrophic to autotrophic tissues (S/F). However, the foliar efficiencies, as measured by annual stem growth per unit of foliar weight (E), of thinned plots were not significantly greater than those of unthinned plots, in spite of the reduced competition and lower S/F ratio. The lack of response of foliar efficiency to thinning is discussed in relation to published information about photosynthetic rates and stem respiration rates. In all stands, the E values of dominant trees were equal to, or less than, those of subordinate trees, in spite of their superior competitive position and lower S/F ratio. The lack of correlation between competitive position and foliar efficiency is also discussed.