Greenhouse gas emissions from forestry operations: a life cycle assessment

Most forest carbon assessments focus only on biomass carbon and assume that greenhouse gas (GHG) emissions from forestry activities are minimal. This study took an in-depth look at the direct and indirect emissions from Pacific Northwest (PNW) Douglas-fir Pseudotsuga menziesii (Mirbel) Franco] forestry activities to support or deny this claim. Greenhouse gas budgets for 408 "management regimes" were calculated using Life Cycle Assessment (LCA) methodology. These management regimes were comprised of different combinations of three types of seedlings (P + 1, 1 + 1, and large plug), two types of site preparation (pile and burn, and chemical), 17 combinations of management intensity including fertilization, herbicide treatment, pre-commercial thinning (PCT), commercial thinning (CT), and nothing, and four different rotation ages (30, 40, 50, and 60 yr). Normalized to 50 yr, average direct GHG emissions were 8.6 megagrams (Mg) carbon dioxide equivalents (CO2e) ha(-1), which accounted for 84% of total GHG emissions from the average of 408 management regimes. Harvesting (PCT, CT, and clear cutting) contributed the most to total GHG emissions (5.9 Mg CO2e per 700 m3 harvested timber), followed by pile and burn site preparation (4.0 Mg CO2e ha(-1) or 32% of total GHG emissions) and then fertilization (1.9 Mg CO2e ha(-1) or 15% of total GHG emissions). Seedling production, seedling transportation, chemical site preparation, and herbicide treatment each contributed less than 1% of total GHG emissions when assessed per hectare of planted timberland. Total emissions per 100 m3 averaged 1.6 Mg CO2e ha(-1) over all 408 management regimes. An uncertainty analysis using Monte Carlo simulations revealed that there are significant differences between most alternative management regimes.