Ethan Tapper, Chittenden County Forester
As the effects of climate change on our world become more and more apparent, it is increasingly important to manage our forests to not just withstand these impacts, but to help mitigate them. Vermont’s forests are a carbon “sink,” capturing (or “sequestering”) more carbon than they emit, and in the course of forest management many foresters seek to increase their ability to sequester and store as much carbon as possible. While wrapping our heads around carbon dynamics can be tricky, it is important to understand the important role that forests play in protecting us from the worst impacts of climate change.
As trees grow, they capture carbon dioxide out of the atmosphere, turning it into biomass (wood and leaves) and releasing oxygen. Carbon sequestered by trees can be found in several places; as wood in living trees, in dead-standing and fallen trees, and, once this dead wood has broken down, in forest soils. As wood decomposes it also releases carbon dioxide back into the atmosphere, though our forests sequester much more carbon than they emit. While you may think that most of the carbon in the forest must be stored in the trunks and branches of our massive trees, in temperate forests (like those in Vermont) it is estimated that up to 50-60% of a forest’s carbon is stored in its soils.
Interestingly, young forests sequester carbon more rapidly than older forests (they grow faster), but older forests store more carbon than younger forests. These seemingly opposite facts have fueled divergent management strategies; the former has been used to justify aggressive logging, while the latter has been used to justify a “hands-off” approach. The picture is further complicated when you consider the benefits of wood products as part of the mix; because dry lumber stores about double its mass in carbon dioxide equivalent, building our houses, buildings and other durable items out of wood fixes carbon in the long term. Using locally harvested and processed wood for building materials, heat and energy also mitigates the need for less carbon-friendly materials shipped from farther away (releasing more carbon dioxide as part of the shipping process). So, while we know that over time unmanaged forests probably store more carbon than managed forests, there are other carbon benefits to harvesting wood through active forest management.
So how can we increase carbon sequestration and storage in our forests? In a word, encouraging “diversity” — many different ages, sizes and species of trees — is a good place to start; more diverse forests generally store more carbon than less diverse forests. Vermont’s land use history has resulted in forests which generally lack diversity, old trees and soil carbon, as compared to the forests that probably existed here prior to European settlement. Active forest management can help forests regain these features more rapidly, increasing diversity while harnessing the sequestration benefits of young, fast growing forests and the storage benefits of old forests, all while producing an output of forest products. Retaining dead standing trees, a lot of dead wood on the forest floor, and “biological legacy” trees — trees that will never be harvested — in the course of forest management will further help our forests store more carbon. All of these features will also create more vibrant wildlife habitat, and forests which are resilient to the disturbances that may become more frequent as our climate changes.
Because of how important to climate change mitigation our forests are, it is also important to protect their health so that they may continue to help us sequester and store carbon, in addition to cleaning our air and water, and providing habitat and refugia for our wildlife, forever. Encouraging the resilience of our forests by managing for forest health, controlling invasive exotic plants and keeping forests undeveloped and unfragmented will help keep forests healthy, in turn helping them sequester carbon and mitigate the effects of climate change in the long term.
For more information on forest carbon storage see:
Forest carbon storage in the northeastern United States: Net effects of harvesting frequency, post harvest retention, and wood products; a 2010 paper from Forest Ecology and Management by Jaren Nunery and William Keeton; and
Vermont Forest Carbon: A Market Opportunity for Forestland Owners a paper published in 2018 by The Spatial Informatics Grou, the Carbon Dynamics Lab at UVM and the Vermont Land Trust, by William Keeton, William VanDoren, Charles Kerchner and Mackenzie Fuqua
Ethan Tapper is the Chittenden County Forester. He can be reached via email, by phone at (802) 585-9099 or at his office at 111 West Street, Essex Junction.