Shoot neoformation in clones of Fraxinus pennsylvanica in relation to genotype, site and pruning treatments

Abstract

Four clones of Fraxinus pennsylvanica var. subintegerrima (Vahl) Fern. were planted in replicated trials at two sites in Manitoba (Morden and Winnipeg) to investigate shoot growth and leaf neoformation in relation to genotype, environment and pruning treatment over a 3 year period. Significant differences were found among clones, years and sites for shoot length and numbers of neoformed leaves. Neoformation was highest shortly after transplanting and then declined. An increase in neoformation was evident following cold related winter injury or loss of terminal buds by late spring frosts. Pruning and terminal bud removal treatments both increased neoformed leaf production relative to control trees. The trees were able to quickly re-establish photosynthetic surface area after injury or treatment and neoformed leaf production was an important component in this recovery strategy. The capacity for neoformation also varied in relation to genotype but appeared to be very plastic, being affected by a wide variety of factors. In addition, the rate or pattern of change in amounts of neoformed leaves over time and locations was variable. Numbers of neoformed leaves increased with shoot length but variation in the relationship suggested that there were differences in internode length as well. Neoformed leaves were highest in the upper part of the crown indicating that there was differential allocation of resources within the crown.