On July 5, the Gazette published an Associated Press article, “How to fight climate change? Plant many trees.”
Swiss scientists publishing in the journal “Science” calculated that “over the decades, those new trees could suck up ... about as much carbon pollution as humans have spewed in the past 25 years. Much of that benefit will come quickly because trees remove more carbon from the air when they are younger.”
Contrary to popular belief, trees do not remove more carbon from the air when younger. Starting from seed, their rapid annual growth rates are apparent, but absolute amounts of carbon sequestered in their trunks and limbs is still small, and remain so for four or five decades.
Additionally, in thickly stocked stands, few seedlings will survive. Still, forest managers commonly believe that young trees sequester (and presumably hold) more carbon because of early rapid growth.
Indisputably, young trees hold less carbon than they will at ages of 50 to 100 years. White pine studies by the Native Tree Society (NTS) in the Northeast show that one pine’s annual increase in carbon sequestration at 100 years is equivalent to the increased sequestration of multiple young pines.
For example, a 30-year-old white pine may hold 200 to 250 pounds of trunk carbon. The same tree can easily hold 1,700 to 1,800 pounds at 100 years, and 2,400 to 2,500 pounds by age 150. Most of the carbon increase comes after 30 years, and significant accumulation continues for decades.
From the NTS study, Bob Leverett concludes that white pines continue to effectively sequester carbon beyond 150 years and in the case of dominant trees, over 200. Ensuring that our existing mature trees are protected should receive the highest priority.
The recent Intergovernmental Panel on Climate Change report states that we only have until 2030 to reduce the difference between the amount of carbon dioxide we emit from all sources (including fossil fuels, biomass burning and land use change) and the rate that natural systems like forests and oceans can remove it from the atmosphere.
Today, forests remove an amount of carbon dioxide from the atmosphere that equals approximately 25 percent of what humans emit. This rate can and must be increased by 45 percent at the same time as we reduce our emissions in order to keep the concentration of heat trapping gases like carbon dioxide at a level that does not (further) disrupt the climate system.
While it is important to plant new trees for the longer term, waiting decades for them to grow will not help us to meet our short-term goals.
Allowing existing trees to continue growing and sequestering carbon is essential. This simple concept is explained in a peer-reviewed paper published by the journal “Frontiers in Forests,” authored by Drs. William R. Moomaw, Susan A. Masino and Edward K. Faison. The paper’s title says it all: “Proforestation Mitigates Climate Change and Serves the Greatest Good.”
Proforestration means “growing existing forests intact to their ecological potential,” and is contrasted with afforestration (planting new forests) and reforestration (replacing forests on deforested or recently harvested lands) that take much longer to remove carbon dioxide from the atmosphere in their early years than older forests do as they continue growing.
Proforestation has the further advantage of not requiring any new land, nor does it have additional labor to plant new trees. These older forests also provide multiple benefits including protecting biological diversity and purifying air and water.
Intact forests of larger trees also provide added resilience to the increased intensity of precipitation events by reducing flooding and soil erosion and cooling the surrounding region by shading and the evaporation of large amounts of water.
The importance of retaining mature trees for greater carbon sequestration is supported by new studies of forests of all types. Globally, the largest 1 percent of living trees worldwide contain half the above ground carbon, and current young forests sequester only half of what they are capable if they were older and larger. Another study found that a 100-centimeter diameter tree annually absorbs as much carbon as an entire 10-20 centimeter tree holds cumulatively.
Allowing forests to grow to their full biological potential is far more effective in mitigating climate change than is cutting down mature trees and planting young ones. Planting trees where they presently do not exist is useful for the longer term, but protecting trees that are already standing ensures a continuing benefit for urgently addressing the climate crisis now.
Dr. William R. Moomaw is emeritus professor at Tufts University and lead author of five Intergovernmental Panel on Climate Change reports. Bob Leverett is a co-founder of the Native Tree Society and Friends of Mohawk Trail State Forest. Pianist Monica Jakuc Leverett is co-founder of the “Monica and Bob Leverett Forever-Wild Conservation Fund” at Kestrel Land Trust. Robert A. Jonas is ex-Board Chair of the Kestrel Land Trust.