Why We Disagree about the Climate Impact of Forestry - A Quantitative Analysis of Swedish Research.

Intensifying forest management or reducing harvest levels are proposed as alternative strategies for mitigating climate change. Today, scientific disagreement over which approach is more effective impedes the development and implementation of effective climate change mitigation policies. In this paper we review studies of the climate impact of Swedish forestry to clarify the conceptual and methodological differences that underly the disagreement. To examine how assumptions concerning crucial parameters contribute to differing conclusions, we simulated various management scenarios for Gävleborg County in central Sweden. We find that support for either side in the debate can be obtained by adjusting assumptions about substitution levels and the design of management interventions. Studies favoring intensified management over reduced harvesting assume relatively high substitution levels and implement intervention levels - such as increased fertilization or expanded stump harvest - which are considerably higher (2.4-17.7 times) than the levels recommended by the Swedish Forest Agency. Conversely, when using recommended intervention levels and substitution levels based on current usage of forest biomass, reduced harvest strategies show greater climate benefits than intensified management. These findings emphasize the need to focus the scientific discussion on i) the empirical evidence for various substitution levels and ii) the relevance of alternative management scenarios for the development of effective climate change mitigation policies.