Pictured here is a Ponderosa pine, Pinus ponderosa. Credit: The authors

图为黄松，图片来源：作者

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

在美国的太平洋西北地区，1994年制定了21英寸直径的规定，以减缓国家森林中大型的老树的损失。但是，对这一限制的拟议修正可能会允许广泛采伐直径最大为30英寸的大树，这对碳动态和森林生态具有重要意义。领导该研究的David Mildrexler博士强调：

“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.”

“大树只占森林中树木的一小部分，但它们在整个森林种群中发挥着极其重要的作用，它们提供的许多独特功能将需要数百年的时间才能被替换。”

To examine the relationship between tree diameter and aboveground carbon storage in forests east of the Cascades Crest, the researchers used species-specific equations to relate tree diameter and height to the aboveground biomass in the stem and branches, taking into account that half this biomass in a tree is comprised of carbon. They also examined what proportion large trees made up of the total forest stand, their total calculated aboveground carbon storage and therefore what the potential consequence of removing these large trees could have within future forest management practices.

为了检查 Cascades Crest 以东森林中树木直径与地上碳储量之间的关系，研究人员使用了物种特有的方程来将树的直径和高度与茎和树枝中的地上生物量联系起来，考虑到树中的一半生物量是由碳组成的。他们还研究了大树占总林分的比例、计算出的总地上碳储存量，以及移除这些大树在未来森林管理实践中可能产生的潜在后果。

The study also revealed that trees >30 inches (>76.2 cm) in diameter only constituted 0.6% of the total stems, but these giants accounted for over 16% of the total aboveground carbon across the forests examined. Once trees reached a large size, each additional increment in diameter resulted in a significant addition to the tree’s total carbon stores:

该研究还表明，直径 > 30 英寸（> 76.2 厘米）的树木仅占总茎的 0.6%，但这些巨型树木占所检查森林总地上碳的 16% 以上。 一旦树木达到大尺寸，直径的每一次增加都会导致树木的总碳储存量显著增加：

“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.”