Document: DAV-3-39-6

The role of Pseudotsuga menziesii as a long-lived pioneer is determined by its processes of foliage regeneration.

ISHII, H.* and E.D.FORD

University of Washington, Seattle, WA 98195, USA ¹

Abstract:
Much old-growth forest in the Pacific Northwest is dominated by Pseudotsuga menziesii. This species is generally considered a pioneer, but unlike pioneers in some other forests it continues to grow while other tree species invade, reach maturity, and die. P. menziesii is a long-lived pioneer. The Wind River Canopy Crane Research Facility was used to make detailed and repeated measurements of tree, crown, and foliage, not previously possible in old-growth forest. Crown development of old-growth P. menziesii has three important characteristics: 1.) The crown height growth is maintained even at +50m tree height while some more numersous tree species in the forest seem unlikely to reach that height. 2.) While the crown is sparse compared to other old-growth species there is continuous production of epicormic branches along tree trunks, and continuous production of epicormic shoots on branches. Over 95% of foliage is on epicormic shoots. 3.) Shoot production rates and branching patterns show acclimation to changing canopy conditions. They are comparable to those of Abies amabilis and Abies grandis, two important shade-tolerant species, and extremenly simplified compared to young P. menziesii. Due to continuing foliage regeneration through epicormic branch and shoot growth, and morphological plasticity in response to changing canopy conditions, Pseudotsuga menziesii is unlike pioneer tree species in some other forest types.

Keywords: Old-growth forest, pioneer, long-lived pioneer, Pseudotsuga menziesii, Douglas-fir, tree crown, foliage canopy.

This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY