Production and mortality are the component processes that together determin
e the biomass dynamics of forests. Due to the significant role of forests i
n the global carbon cycle, it is important to assess how these two processe
s affect the maximum biomass attained by forests, as well as the dynamics l
eading up to and following peak biomass. We address these questions for two
sets of plots in Picea stichensis-Tsuga heterophylla forest on the norther
n Oregon coast: that originated from a catastrophic wildfire in the 1840s,
using new data on dynamics of live trees and stocks of coarse woody debris
(CWD). The set of plots closest to the ocean and occupying steeper, more di
ssected terrain with areas of thin soils has lower biomass, lower net prima
ry production (NPP) of bole wood and higher, tree mortality as a fraction o
f standing biomass. The two sets of plots have similar CWD levels, most of
which has accumulated in the last 25 yr. The present dispar ity in biomass
between the two sets of plots appears to be the result of lower NPP on the
low-biomass plots for the entire 140+ yr history of the forest. Over the 58
yr that the high-biomass plots have been measured (from stand age 85 to 14
3 yr), NPP of bole wood has declined by 41%. Only ca. 6% of this decline ca
n be accounted for by an increase in maintenance respiration of woody tissu
es. For both sets of plots relative constancy of biomass in the long term a
ppears likely, due to a short time lag in tree regeneration, asynchronous t
ree mortality and little overall decline in NPP of bole wood in recent deca
des. However, since tree mortality as a fraction of stranding biomass is hi
gher on the low-biomass plots, and NPP of hole wood is slightly lower, the
difference in biomass between the two sets of plots should increase if curr
ent rates of production and mortality persist.