Modeling the climate mitigation potential of beetle-kill-to-biofuel/biochar systems: The Bioenergy Alliance Network of the Rockies

Carbon accounting at the nexus of forest management and bioenergy production has long been complex and controversial, particularly regarding whether woody feedstocks can be sustainably sourced without counter-productive reductions in forest ecosystem carbon storage. In the western U.S., recent bark beetle outbreaks have caused widespread tree mortality across more than 40 million acres of pine and spruce forests, slowing or even reversing their near-term carbon sink value. Often there is ‘push’ from land managers to remove beetle-killed trees in the interest of extracting timber value, reducing fuels, and protecting critical infrastructure. While such treatments can be cost-prohibitive, the use of non-merchantable wood fractions for bioenergy production might potentially add market ‘pull’ and enable treatment of larger areas of beetle-kill forest. The Bioenergy Alliance Network of the Rockies has been assessing the economic, environmental, and social sustainability of such a potential new regional bioenergy industry. In this presentation we describe our preliminary efforts to estimate the climate impacts of beetle-kill harvest for bioenergy production at the regional scale in northern Colorado and southern Wyoming. Specifically, we consider whether and over what time-scales the potential climate mitigation benefits of biofuel and biochar co-production might outweigh the ecosystem carbon losses of harvesting those dead trees. We have extensively calibrated and validated the Forest Vegetation Simulator (FVS) model to better represent post-disturbance dynamics in local lodgepole pine and aspen stands. Coupling Forest Inventory and Analysis program plot data, FVS modeling, and machine learning techniques enables estimation and spatial interpolation of the ecosystem ‘carbon debt’ of beetle-kill harvests over time, as compared to a no-harvest status quo. We then couple these results with a simple mass balance for a local industry partner’s thermochemical conversion process producing gasoline blend-stock and a biochar co-product. We will present our preliminary regional-scale climate mitigation assessment results, and quantify the sensitivity to various ecosystem and technology factors