CHANGES IN BIOMASS AND PRODUCTION OVER 53 YEARS IN A COASTAL PICEA-SITCHENSIS - TSUGA-HETEROPHYLLA FOREST APPROACHING MATURITY

At Cascade Hand Experimental Forest, Oregon, biomass of bolewood increased from 570 Mg.ha-1 at age 85 yr to 760 Mg.ha-1 at age 138 yr. Net primary production of bolewood declined from 11 to 6 Mg.ha-1.yr-1, and mortality loss increased from 2 to 6 Mg.ha-1.yr-1. Values for 37-yr-old plots in the same area were 210-360 Mg.ha-1.yr-1 bole biomass, 7-20 Mg.ha-1.yr-1 bolewood production, and 0-2 Mg.ha-1.yr-1 mortality loss. Of the photosynthate potentially available for bolewood production, some replaces biomass lost via mortality and some is allocated to maintenance (respiration plus allocation to fine roots). A quarter to 1/2 of the production is lost by mortality; mortality loss may thus be an important factor limiting forest biomass accumulation. -from Authors