JUNIPERUS OCCIDENTALIS JUVENILE FOLIAGE - ADVANTAGES AND DISADVANTAGES FOR A STRESS-TOLERANT, INVASIVE CONIFER

Physiological processes for juvenile and adult foliage of Juniperus oc cidentalis Hook. were compared to evaluate the advantages and disadvan tages of juvenile foliage for a stress-tolerant, invasive conifer. Abo ve- and below-ground biomass allocation and monthly measurements (Apri l through October) of gas exchange, water relations, foliar nitrogen c oncentrations, and growth were made for juvenile and small-adult trees in the field in central Oregon. Compared with small adults, juveniles have greater allocations to foliage and fine-root biomass, higher rat es of CO2 assimilation, leaf conductance, and transpiration, and lower investments of biomass and nitrogen per unit of foliar area. Juvenile foliage is less costly to produce than adult foliage. The suite of ph ysiological processes associated with juvenile awl-like foliage should enhance establishment and early growth of J. occidentalis. However, h igh rates of water loss, which are associated with high rates of CO2 a ssimilation of juvenile foliage, appear to be a liability for large tr ees in the semiarid environment of eastern Oregon. Once established, t he transition to a more conservative use of resources associated with adult scale-like foliage is consistent with the stress-tolerant strate gy of long-lived evergreen trees.