EFFECTS OF THINNING ON THE ALLOCATION OF GROWTH AND RESPIRATION IN YOUNG STANDS OF BALSAM FIR

The current annual growth of foliage, branches and stems per unit of foliar weight was approximately the same in unthinned stands of young balsam fir (Abies balsamea (L.) Mill.) and stands thinned 4-6 years earlier. Foliage branches, and stems accounted for approximately 30, 30, and 40%, respectively, of aboveground growth in the thinned and unthinned stands. The allocation of photosynthates to stems was estimated by adding the carbon used for respiration to that used for growth. The proportion of photosynthetic production allocated to stems was greater in an unthinned stand than in a thinned stand. The additional proportion of net photosynthetic production allocated to stems in the unthinned stand was used for maintenance respiration. Since the photosynthetic production per unit of foliar weight of thinned stands should equal or exceed that of unthinned stands, differences in the proportion of photosynthates allocated to stems between these stands imply differences in the proportion of photosynthates allocated to other tree components. Therefore, it appears that a larger proportion of photosynthates was allocated to branch respiration and (or) roots in thinned stands than in unthinned stands.