Logging and carbon sinks

Forests are getting a second look, not as a source of wood products but as buffers against climate change

Logging and carbon sinks
Caption: a logging operation with a forwarder (the blue machine) for transporting logs. Forwarders are less damaging to the forest than the more commonly used skidders.

A few residents have expressed concerns about various logging jobs in Thetford that are currently underway. Rest assured that those logging jobs, irrespective of their perceived impact or size, are entirely legal, and anyone may contact the county forester to check (david.paganelli@vermont.gov).  

Many landowners who log their land do so to comply with Current Use. Back in 1978 the Vermont legislature enacted the Current Use Program, with the objective of keeping Vermont’s agricultural and forest land in production. The law allows the valuation and taxation of such land to be based on keeping it in agricultural or forestry use, rather than land that could be developed. Other goals were to help slow the loss of farms and forests, and to achieve greater equity in property taxation on undeveloped land. Not all forest owners enroll, and an average of 20,000 acres per year were lost from the forest land base in Vermont between 2012 and 2017.

To be eligible for Current Use, parcels must contain at least 25 contiguous forest acres. A forestry management plan that is approved by the Vermont Department of Forests, Parks and Recreation is also required. Management plans ensure that there is periodic logging to keep the land in production.

But forests are getting a second look, not as a source of wood products but as buffers against climate change. Forests are the only proven system that removes carbon dioxide from the atmosphere, and, when left to their own devices, they store it long-term. There are forests in the world that are estimated to be thousands, even millions, of years old. In the US, trees over 800 years old may be found in the Tongass forest in Alaska. Several administrations have placed this forest on the chopping block.

Here in Vermont there is a lot of forest, about 4.5 million acres according to the VT Department of Forests and Parks. By their very existence, Vermont forests hold in storage over 1.7 billion metric tons (tonnes) of carbon dioxide (CO2) equivalents. And each year they take in a further 5 million tonnes of CO2 equivalents. On the other hand, Vermonters collectively emit about 8 million tonnes of CO2 equivalents in a year. Taking these statistics to a smaller level, one average Vermonter emits 15.6 tonnes of CO2 equivalents/year, while one acre of average forest sequesters 1.3 tonnes of CO2 equivalents/year. So, 12 acres of average forest are necessary to remove the CO2 emissions of the average Vermonter — or 7.7 million acres for the 2021 census population. This does not take into account cars; one average car emits 4.5 tonnes of CO2 equivalents/year.

As mentioned, trees sequester carbon long-term. Yet forestry plans call for cycles of logging every several decades. The rationale is an economic one; when trees surpass a certain age, the quality and commercial value of the timber decreases. Logging is also an opportunity to remove trees with “declining vigor” and “poor form” and to thin trees in “overstocked” stands. So trees are cut, they re-grow for several decades, and they are cut again.

Caption: high quality ash hardwood logs

What does this look like from the carbon sequestration angle? If old, unmanaged forest is compared with a forest managed on a 60-year rotation, the carbon stored per hectare is 611 tonnes for the unmanaged forest and 274 tonnes for the managed forest. It is true that carbon continues to be stored in wood products from managed forests, as long as they are not eventually burned. However, if the priority is keeping carbon out of the atmosphere, unmanaged forests still come out on top. Even when old trees die, they continue to store carbon, and when they fall and decay they feed the soil biosphere. A portion of the carbon is locked up in the form of humus. As any gardener understands, humus is a key element in soil health and retention of soil nutrients.

A forest is more than trees growing together; it is akin to a single living organism. Underground, trees are intimately interconnected by a myriad of fungal threads that actually penetrate tree roots. Through this, trees transfer sugars from photosynthesis to the fungi in exchange for minerals that fungi absorb from weathering bedrock.

Trees transfer nutrients to other trees through the fungal network, thus supporting juvenile trees that are too shaded by the “mother” tree to perform photosynthesis. They also feed nearby trees if they are sickly. If a tree is attacked by pests, it sends “alarm” signals to the surrounding trees, prompting them to make protective compounds.

Large old trees with huge numbers of fungal connections are comparable to the hubs on an airline network. When a healthy old tree is abruptly felled, its fungal connections die, leaving a large void. There is evidence that the fungal network does not recover, for reasons unknown. By contrast, it takes decades for a tree to die naturally, allowing the fungal network to reconfigure. As a tree dies, it sends all its nutrients out to the surrounding trees.

The urgency of climate change calls for a rapid evolution in Current Use forestry plans to make the most of our carbon-saving trees and protect their health. In 2020 the Vermont Forest Carbon Sequestration Working Group investigated the viability of enrolling Vermont forests into carbon offset markets. But can this approach work in Vermont? The average size of a carbon offset project in the northeast US is 39,675 acres. Vermont forestland is generally in private parcels too small to enter into carbon markets. Aggregation of parcels en masse would be necessary. The complexities and long-term commitment (40-100 years) are likely to be disincentives.  

The House Natural Resources Committee is exploring a change that would allow family forest owners to enroll permanently conserved, forever-wild forests into Current Use. Other ideas include adopting a three-pronged management approach that includes production logging, ecological forestry, and wildland forestry.  We can only hope that a good decision comes soon.

Locally, the forest management plan for Town of Thetford-owned forests is coming up for review.

Photo credit: Li Shen

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