Carbon and Forests

Diagram of the global climate cycle.

Global carbon cycle. Credit: Climate Change Resource Center

Carbon is one of the most abundant elements on earth and it serves as the building block for all life. It is found as an organic molecule in living and dead organisms, as carbon dioxide gas in the atmosphere, as organic matter in soils, as fossil fuels and sedimentary rock deposits, and in multiple forms in the oceans. The processes governing carbon fluctuations in these different areas are complex and variable, and they have substantial impacts on the conditions of the planet.

Diagram of the forest carbon cycle.

The closed loop of carbon in the atmosphere. Credit: USFS Carbon Cycle

Forests are a critical component of the global carbon cycle. They are dynamic systems, constantly absorbing and releasing carbon dioxide. Carbon sequestration is the process of removing carbon from the atmosphere for use in photosynthesis. This results in the maintenance and growth of plants and trees. Generally, carbon sequestration rates are greater in younger (20-70 year old) forests, when growth rates are highest.

Carbon storage is the amount of carbon retained in a given area. The amount of carbon stored in a forest at any given time is influenced by several factors. Generally, carbon storage is greater in older forests and structurally complex forests. Forest structure is defined by the size, arrangement, and condition of trees and other vegetation. A structurally complex forest is one with large trees, small trees, live trees, dead trees (standing and downed), and understory, midstory, and overstory vegetation arranged together. Densities of any one size or condition of vegetation may vary.

Carbon resides in forests in different places for different amounts of time. A carbon pool is a part of the forest that stores carbon (see diagram below). The amount of carbon stored in any one pool changes over time.

Carbon pools

Forest carbon pools and the approximate breakdown of the percent carbon stored and sequestered. Source: Domke et al. 2020

Factors that influence the amount and proportion of carbon in each pool are: forest age, species composition, natural and human disturbances, soil characteristics, and land-use history. 

An important and often overlooked carbon pool is that of wood products. Did you know that 50% of a tree's biomass is carbon? Most of that carbon is retained when the harvested tree becomes a durable wood product (furniture, flooring, etc.). This is an important carbon pool, as the use of durable wood products, particularly those derived from local or regional harvests, reduces carbon emissions associated with carbon-intensive materials such as concrete, steel, and plastics. When done correctly, harvesting trees from the forest to make wood products also creates favorable conditions for the removal of additional carbon dioxide from the atmosphere. In fact, for every one cubic foot of wood harvested from Connecticut’s forests, over six cubic feet of wood grows.

Leakage is a critical consideration when assessing the role of forest management and harvested wood products in the carbon cycle. Reducing forest management of wood products in Connecticut or New England does not benefit the carbon cycle if those wood products are being sourced from unregulated and geographically-distant systems. 

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Content last updated in April 2021.