In the face of worsening climate breakdown, what is the most immediately effective forestry solution? Planting new trees or preserving old-growth forests? Maybe comparing carbon sequestration and carbon storage could give us an answer...
Old Growth Forests Overview
As the name suggests, old-growth forests are forests that have been uncut and undisturbed for hundreds of years. Because of the variety of tree species, it is difficult to determine an age threshold for old-growth forests. In the 1940s, when old-growth forests became points of interest, trunk diameter at shoulder height was the best indicator. Ideas of what constitutes an old-growth forest expanded with the environmental movement of the 1970s and was defined by the Forest Service in the late 1980s:
"Old-growth forests are ecosystems distinguished by old trees and related structural attributes. Old-growth encompasses later stages of stand development that typically differ from younger stages in a variety of characteristics that may include tree size, accumulations of large dead woody material, number of canopy layers, species composition and ecosystem function."Still, the characterization of old-growth forests differs from region to region and is based on vegetation type.
Old Growth is More Than Just Tree Size
Among the unique features longevity has allowed old-growth forests to develop, canopy soils have emerged as a new focus of forestry research. Canopy soils are formed as fallen leaves and other organic material accumulate on dense clusters of tree branches over hundreds of years. Over time, a carbon-rich layer of soil several inches thick is formed. Researchers Hannah Connuck of Franklin and Marshall College and Peyton Smith of Texas A&M University found that canopy soil stores three times more carbon than ground soils, making canopy soils an important contributor to old-growth forests as carbon sinks. The time necessary for old-growth forests to mature and for canopy soils to develop makes them irreplaceable in, not only our lifetimes, but also in the short time we have to avoid climate breakdown beyond control.
Source or Sink? Young vs. Old
Fundamental Facts:
-During photosynthesis, trees absorb carbon (as CO2) as a reactant to synthesize sugars.
-During cellular respiration, trees emit carbon (as CO2) as a product to generate energy.
-For a forest to be a net carbon sink, its trees have to collectively photosynthesize at a higher rate than they respire.
Young Forests- between 15 and 30 years
Sequestration rank- #2: Since young forests are still growing, they intake carbon at a higher rate than mature and old forests to build their structural biomass. Still, they photosynthesize less than mature and old trees because of smaller leaf surface area and, therefore, less chloroplasts (photosynthesis organelles). Storage rank- #2: Because of their size, young forests cannot store as much carbon as old forests. No carbon-storing canopy soils have developed (over multiple life cycles and dense branch systems) yet.
Young forests are net carbon sources. Even so, they are necessary to continue fighting climate breakdown in the long term.
Old Forests- 200+ years
Sequestration rank- #1: Though counterintuitive that old forests sequester more carbon ("they don't need anymore carbon to grow!") than young forests, because of the larger number of leaves on trees and ground vegetation, old forests sequester incredible amounts of carbon. Old-growth forests on the coast of Oregon sequester more than the Amazon!
Storage rank- #1: The larger the trees, the more carbon is stored in the massive trunks, dense branches, and thick leaves. The older the ecosystem, the more carbon is stored in developing, carbon-rich canopy soils.
Old forests are net carbon sinks. Their preservation is necessary to slowing climate breakdown now.
Dangers to Old-Growth Forests
Quality wood products (usually furniture and instruments) are the main reason old growth trees are lumbered. Old-growth wood is sturdier, more resistant to rotting, and has tighter growth rings.
Old-growth trees are also cut down for the disproven belief that "they're just too old, are about to die, fall down, and cause a fire." However, most old-growth trees stay alive for decades after full growth. Trees that die and stay standing—snags—are important habitats and nesting sites for birds. If trees die and fall in numbers large enough to contribute to fire fuel, it is often indicative of an underlying problem in the forest such as drought or disease.
When old-growth trees are harvested, only 20% of the wood is used for long-term products (4). Short-term products, such as newspapers and shipping boxes, are thrown within 20 years (4). Still, 65% of the carbon from old-growth harvests is emitted to the atmosphere within 30 years (4).
How to Protect Forests—Old and Young?
Since settlement in North America, 95% of Western forests and 99% of Eastern forests have been logged for development. The majority of those remaining are threatened by climate breakdown and further development.
Among the recent initiatives taken to protect our forests is Executive Order 14072, released on Earth Day 2022, which sets goals and requirements for U.S. Departments of Agriculture, of the Interior and for the government in general.
The Old-Growth Forest Network, founded by Joan Maloof of Salisbury University, maps out old-growth forests in the country and aims to have one protected forest in each U.S. county. The closest forest to Towson listed in the Old-Growth Forest Network is the Mt. Washington Arboretum, a collection of trees and shrubs cultivated and labeled for educational and scientific purposes. Visiting forests in the area is the best way to develop commitment to preserving the natural environment of the county, state, and country.
Still, planting the young trees that will grow into old-growth forests remains an undeniable mean of investing in climate stability for the future.
Written by Miriam Dia '23.
Sources: (1) Old Growth Forests. Forest Service- U.S. Department of Agriculture. https://www.fs.usda.gov/managing-land/old-growth-forests
(2) Soils in old-growth treetops can store more carbon than soils under our feet. Science News. December 16, 2021. https://www.sciencedaily.com/releases/2021/12/211216150334.htm
(3) Williams, J. Visible Forest Stages. Salish Magazine. https://salishmagazine.org/forest-stages/
(4) "The Surprising Truth Behind Planting Trees and Climate Change." YouTube, uploaded by PBS Terra, 18 October 2021, https://www.youtube.com/watch?v=LDdKOmvIKyg
(5) Old Growth vs. New Growth Lumber - Which Is Better? Urban Wood Goods. https://urbanwoodgoods.com/blogs/news/old-growth-vs-new-growth-lumber-which-is-better
(6) Why Old-Growth Forests? Old-Growth Forest Network. https://www.oldgrowthforest.net/why-oldgrowth-forests
(7) McKie, R. The Methuselah Tree and the Secrets of Earth's Oldest Organisms. The Guardian. 2 August 2020. https://www.theguardian.com/environment/2020/aug/02/the-methuselah-tree-and-the-secrets-of-earths-oldest-organisms