Conservation or Harvesting? Carbon Dynamics of Old-Growth Forests in Coastal British Columbia

Old-growth forest can play an important role in a regional carbon cycle, but their potential in carbon sequestration is debated. The scientific literature has divided results on whether conservation of forest is a net benefit to climate change mitigation under changing climate, management strategies, and disturbance regimes. To provide useful information for decision making, we need to identify under which conditions conservation or harvesting is better for carbon. Therefore we must evaluate the net carbon sink/source of not only the forest ecosystem but also the carbon stocks and emissions of Harvest Wood Products (HWP) and their carbon emission reduction when used to substitute high emission materials. In this study, we used field measurement date from over 2000 forest plots in coastal British Columbia to parameterize and calibrate hypothetical landscapes of three different productivity levels. A landscape model, LANDIS-II with the Forest Carbon Success Extension, were used to stimulate the carbon dynamic in the forests. In harvested landscapes, the carbon balance of HWP were simulated using BC-HWPv1 model. The results shown that in the conservation scenarios, the over 250 year old forests are a net carbon sink. Inducing clear-cut with 70 years rotation period will turn the 10,000 ha landscape into a significant carbon source in the following decades. In the low productivity landscape, the net ecosystem production (NEP) of the forest is still negative 150 years after the start of harvesting. In the median and high productivity landscapes, the forest regrowth increased the carbon sequestration rates in the ecosystem, however the positive sinks did not balance out the cradle-to-grave carbon emissions from HWP, making all the harvested landscapes a net source in the 150 years post harvest. The impact of climate change, wind-throw and wildfire, wood products substitution, and harvesting with an extended rotation period will be evaluated in the same modeling frame work. This study develops systematic approaches, integrating all the carbon sinks and sources to quantify the climate mitigation potential of forest conservation. The results will provide insight on forest management and an assessment tool for policy making.