Mark E. Harmon, Richardson
Chair Forest Science, Oregon State University, Corvallis, OR
Forests may have an important role to play in
removing carbon dioxide from the atmosphere.
The exact role they play is dependent not only on the area available for
management but also the management system that is applied and whether it is
based on sound scientific principles including those of basic ecosystem
science. Assessing forest management
strategies involves field studies of processes and changes in stores over
succession, modeling of alternative systems, and consideration of questions of
scale in the application of these results.
The influence of live tree and coarse
woody debris (CWD) on NEP (Net Ecosystem Production) over secondary succession
has been conducted using data collected along a 500-year chronosequence on the
Wind River Ranger District, Washington.
Simple statistical models of live and dead wood accumulation and
decomposition predicted the transition from negative to positive NEP occurred
between 0 and 57 years after disturbance
depending upon the amount of wood left after disturbance. These data indicate that at a rotation age
of 80 years, regenerating stands stored approximately half the wood C as
remaining nearby old-growth forests (age ~500 years), indicating conversion of
the latter forests to younger managed forests results in a significant net
release of C to the atmosphere.
.Simulation models including the key ecosystem processes of
growth, mortality, and decomposition have indicated that agricultural fields
stored the least (15% of the maximum) and forests protected from fire stored
the greatest amount (93% of the maximum) of landscape level C. Conversion of old-growth forests in Oregon and
Washington to any other management or disturbance regime resulted in a net loss
of C, whereas conversion of agricultural systems to forest systems had the
opposite effect. The three factors, in
order of increasing importance, most crucial in developing an optimum C storage
system were: 1) rotation length, 2) amount of live mass harvested, and 3)
amount of detritus removed by slashburning.
C stores increased as rotation length increased, but decreased as
fraction of trees harvested and detritus removed increased. Simulations indicate partial harvest and
minimal fire use may provide as many forest products as the traditional clear
cut/broadcast burn system while increasing C stores. An adequate supply of wood products may not therefore be
incompatible with a system that increases C stores. Application of these results when assessing management systems
requires consideration to scaling. By
paying closer attention to scale, seemly contradictory results concerning
forest management and carbon sequestration can be resolved. This in turn can lead to the development of
a viable carbon sequestration policy.