RECOVERY PROCESSES OF PONDEROSA PINE REPRODUCTION FOLLOWING INJURY TO YOUNG ANNUAL GROWTH

Abstract

Unmistakable evidence of substitute budding in browsed ponderosa pine seedlings was observed in the forests of N. Arizona in 1925-26. This was considered most unusual because there seemed to be a common belief that losses of terminal buds or shoots cut short the development of young pines and that when the primary leader and laterals were destroyed, recovery depended on growth of an uninjured lower branch. Intensive investigations of grazing in relation to natural forest regeneration, conducted in the same region between 1927 and 1937, revealed several processes by which pines commonly replace lost shoots. On plants 3 yrs. old and older young long shoots die when bitten off or destroyed by tip moth to a point below all needle bundles; when one or more needle bundles are left on the stub of an injured leader, the eye initial between the needles of some short shoot developed into a bud and long shoot. When injured shoots die for want of foliage, dormant whorl buds on the older stems spring to life and in the absence of these buds on previously injured stems, secondary buds may develop in the axils of scales. Other growths were also observed, some of which may be adventitious. Juveniles under 3 yrs. of age also develop substitute growths. When the cotyledons are destroyed new growths having primary leaves develop from the growth point above the cotyledons. When the leading growth on 1- or 2-yr.-olds is bitten off leaving primary leaves, dormant buds in the axils of some of them produce new growth with primary leaves. Tree growth from stump or trunk sprouts, particularly of hardwoods, sometimes are bushy or coppicelike; no such tendencies have been observed in pine poles that develop from extraordinary buds.