Elderly, large-diameter trees have been shown to store disproportionally massive amounts of carbon compared to trees that are smaller, highlighting their importance in mitigating climate change, according to a new study in Frontiers in Forests and Global Change. They found that despite accounting for 3% of the entire number of trees on the studied inhabitants, large trees stored 42 percent of their total above-ground carbon within those forest ecosystems. This study is among the earliest of its kind to report the way the proposed policy could influence carbon storage in forest ecosystems, potentially weakening protections for large-diameter trees and resulting in enormous releases of carbon dioxide into the air at the face of a changing climate.
At the Pacific Northwest area of the US, a 21-inch diameter guideline was commissioned in 1994 to impede down the loss of large, older trees in national forests. However, suggested amendments to this limitation would potentially enable widespread harvesting of trees up to 30 inches in diameter with major implications for carbon monoxide and forest ecology. Dr David Mildrexler, who headed the study, highlights:
“Large trees represent a small proportion 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.”
Carbon storage in forests east of the Cascades Crest, the researchers used species-specific equations to relate tree diameter and height into the aboveground biomass in the stem and branches, taking into account this biomass in a tree is comprised of carbon. They also examined what proportion large trees composed of the total forest stand, their total calculated aboveground carbon monoxide and therefore exactly what the potential consequence of eliminating these big trees could have within future forest management practices.
Diameter only comprised 0.6% of the total stems, but these giants accounted for over 16% of their total aboveground carbon across the forests examined. After trees reached a large size, each added increment in diameter resulted in a significant improvement to the tree’s total carbon stores:
“If you think of adding a ring of new growth to the circumference of a large tree and its branches every year, that ring adds up to a lot more carbon than the ring of a small tree.’ explains Dr Mildrexler. “This is why specifically letting large trees grow larger is so important for climate change because it maintains the carbon stores in the trees and accumulates more carbon out of the atmosphere at a very low cost.”
The analysis highlights the importance of protecting existing big trees and strengthening the 21-inch rule to ensure carbon is accumulated since 21-30″ diameter trees are allowed to continue to grow to their environmental capacity, and allowing a sufficient amount of sub-21 inch trees grow farther and become further big, effective carbon shops.
Dr Mildrexler argues that this is among the most effective short-term options for stabilizing climate change and providing other invaluable ecosystem services:
“Large trees are the cornerstones of diversity and resilience for the entire forest community. They support rich communities of plants, birds, mammals, insects, and micro-organisms, as well as act as giant water towers that tap into groundwater resources and cool our planet through evaporation.”
“There is a real need for monitoring forest condition beyond what the forest service does on their inventory plots, and so local communities can also play their part to provide citizen science data and learn about the living forests on their lands, contributing to community income and mitigating climate change.”
Related Journal Article: https://www.frontiersin.org/articles/10.3389/ffgc.2020.594274/full