Larger trees capture most of the carbon: large trees dominate carbon storage in forests

Older, large-diameter trees have been shown to store disproportionately large amounts of carbon than smaller trees, highlighting their importance in mitigating climate change, according to a new study in Forest borders and global change. Researchers looked at aboveground carbon storage of large diameter trees (> 21 inches or> 53.3 cm) on National Forest land within Oregon and Washington. They found that despite accounting for only 3% of the total number of trees on the plots studied, large trees stored 42% of the total aboveground carbon within these forest ecosystems. This study is among the first of its kind to report how a proposed policy could affect carbon storage in forest ecosystems, potentially weakening protections for large trees and contributing to massive releases of carbon dioxide into the atmosphere in the face of a climate that changes.

In the Pacific Northwest region of the United States, a 21-inch diameter rule was enacted in 1994 to slow the loss of large and older trees in national forests. However, the proposed changes to this limit would potentially allow widespread harvesting of large trees up to 30 inches in diameter with important implications for carbon dynamics and forest ecology. Dr David Mildrexler, who led the study, points out:

“Big trees represent a small percentage of trees in the forest, but they play an exceptionally important role in the entire forest community – the many unique functions they provide would take hundreds of years to replace.”

To examine the relationship between tree diameter and aboveground carbon storage in forests east of Cascades Crest, the researchers used species-specific equations to correlate tree diameter and height to aboveground biomass in the trunk and in the branches, taking into account that half of this biomass in a tree is composed of carbon. They also looked at the proportion of large trees made up of the total forest area, the total carbon storage calculated above ground and thus what potential consequence the removal of these large trees could have in future forest management practices.

The study also revealed that trees> 30 inches (> 76.2 cm) in diameter made up only 0.6% of the total stems, but these giants accounted for more than 16% of the total aboveground carbon in the forests surveyed. Once the trees reached a large size, each further increase in diameter resulted in a significant addition to the tree’s total carbon reserves:

“If you plan to add a ring of new growth to the circumference of a large tree and its branches each year, that ring adds much more carbon than the ring of a small tree.” explains Dr Mildrexler. “This is why letting large trees grow is so important to climate change, because it keeps the carbon stores in the trees and accumulates more carbon from the atmosphere at a very low cost.”

The study emphasizes the importance of protecting existing large trees and enforcing the 21 inch rule so that additional carbon is accumulated as 21-30 “diameter trees can continue to grow to their ecological potential and let a sufficient number of sub-21 inch trees grow further and become large and effective additional carbon stores.

Dr Mildrexler says this is among the most effective short-term options for stabilizing climate change and providing other valuable ecosystem services:

“Big trees are the cornerstones of diversity and resilience for the entire forest community. They support rich communities of plants, birds, mammals, insects and microorganisms, as well as serve as gigantic water towers that tap into groundwater resources and they cool our planet through evaporation. “

“There is a real need to monitor forest conditions beyond what the forest service does on their inventory plots, and so local communities can also do their part to provide citizen science data and learn about living forests. on their lands, contributing to community income and mitigating climate change “.

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