Effects of adventitious roots on age determination in Balsam fir (Abies balsamea) regeneration

Abstract

The age structure of balsam fir (Abies balsamea (L.) Mill.) regeneration is frequently used to investigate boreal forest dynamics of North America. Tree ages are usually estimated by counting annual growth rings at the shoot-root interface located above or close to the root system. Inaccurately locating the shoot-root interface could lead to imprecise age determination. In this study, balsam fir seedlings (<2 m height) were harvested in whole from closed forest stands located in the province of Quebec, Canada. Seedling age was determined by (i) counting the number of annual growth rings at the presumed shoot-root interface, and (ii) counting all terminal bud scars from the apex to the base of the hypocotyl (true collar). For all seedlings with adventitious roots, the number of terminal bud scars on the entire trunk was higher than the number of growth rings at the shoot-root interface. The formation of adventitious roots on the belowground trunk was accompanied by a reverse taper phenomenon, i.e., the number of annual growth rings decreased from the presumed shoot-root interface to the true collar. Counting annual growth rings at any level on the trunk of balsam fir seedlings that form adventitious root systems would not be reliable, underestimation's exceeding 20 years are possible and the resulting age structures could lead to erroneous interpretations of regeneration dynamics.