Will global forests slow, or speed, the observed increases of atmospheric CO2? What has been the effect of human use of forest resources and materials extracted from them? A systems approach balances net CO2 removals from the atmosphere (photosynthesis) with net CO2 returns (combustion, respiration and decomposition). The carbon budget model (CBM) must identify all C flows and net changes in C storage pools; it must conserve C. Net ecosystem production (NEP) is a good indicator of system performance when extended to account for C biomass removed as forest products. For policy purposes (scenarios), the CBM must be dynamic and include processes affecting life-cycles of forest ecosystems (e.g., disturbance affects on age-class) and forest products (e.g., recycling or energy substitutions).
Over time, global NEP has changed due to both human perturbations and natural variability. Until recently, emphasis has focused on human factors, regarding forests not directly affected by land-use or land-use change to be in equilibrium (NEP = 0). This assumption is clearly untenable for a changing global environment. How much of the present 'missing sink' can be explained by additional nonequilibrium terms? Will these new sink terms be sustained in the changing environment of the future? The answer has important global policy implications.
This paper summarises the results of a recent NATO Advanced Research Workshop on "the role of forest ecosystems and forest resource management in the global carbon cycle" held in Banff, Alberta. The paper focuses on the dynamics of forest carbon pools over the last century and on changes that might occur in the next 50 to 100 years.
Key words: carbon cycle, NEP (net ecosystem production), environment, climate change, missing sink.
Correspondence: Mike Apps, Northern Forestry Centre, Canadian Forest Service, 5320 122 Street, Edmonton, Alberta, T6H 3S5, Canada
Telefax: +1-403-4357359
E-mail: mapps@nofc.forestry.ca