Guidelines to Aging Western Red-Cedars
Image courtesy of Washington State Department of Natural Resources
The best resource I’ve found for understanding how to approximate the age of Western Redcedars is a research guide titled '“Identifying Mature and Old Forests in Western Washington.” It was written by Robert Van Pelt and is available online as a free download. Here’s a link.
Educated guesses are as close as you’re going to get to assigning an age to an ancient Western Redcedar. Principally, this is because older Western Redcedars decay at their core, which eliminates the option to count annual growth rings.
Here is a summary of the major considerations that Mr. Van Pelt discusses in the article "Identifying Mature and Old Forest in Western Washington" with respect to determining the age of trees in Western Washington:
Tree size and growth form: Old trees tend to have larger diameters, thicker bark, and a more irregular or "gnarled" growth form compared to younger trees.
Tree species: Different tree species have different lifespans, and knowing the typical lifespan of a tree species can provide a rough estimate of its age.
Stand history: Examining the history of the forest stand, including past disturbances such as fire, logging, or insect outbreaks, can provide clues about the age of the trees in the stand.
Site characteristics: The site characteristics, such as soil type and moisture levels, can affect the growth rate of trees and provide additional information for estimating their age.
Associated plant species: Certain plant species, such as under-story herbs, may be indicative of old-growth conditions and can be used to infer the age of the forest stand.
Snags and downed logs: Snags and downed logs are often present in old-growth forests, and their size and stage of decay can provide additional clues about the age of the forest stand.
I am going to assume that what Mr. Van Pelt has to say about Western Redcedars in Western Washington also applies to Western Redcedars found here in my valley, because I could literally walk from my home to Western Washington. It would suck, but I could do it.
Here are some of the specific considerations that Mr. Van Pelt discusses in the article for determining the age of Western Redcedars specifically:
Western Redcedars can live for over 1,000 years and can be some of the oldest trees in the region.
The growth rings of Western Redcedars can be difficult to distinguish due to the tree's irregular growth patterns. Taking multiple measurements and averaging them can provide a more accurate estimate of the tree's age.
The age of Western Redcedars can also be estimated by examining the size and distribution of snags and downed logs in the surrounding area. Old-growth forests often contain large snags and logs, which can provide clues about the age of the forest stand.
Western Redcedars can form "nurse logs," which are fallen trees that provide nutrients and a substrate for new trees to grow on. The age of the Western Redcedar can be estimated based on the age of the surrounding trees growing on the nurse log.
I suspect that most people assume that a large trunk diameter has a high positive correlation with a tree’s age. However, trunk diameter alone is not always the best indication of a tree's age. In Mr. Van Pelt’s article he states:
"The diameter of a tree is often used as a rough estimate of its age, but this method can be inaccurate, especially in older trees. As trees age, their growth rate often slows down, and the diameter of the trunk may not increase significantly for many years. In some cases, the trunk may even shrink as the tree puts more resources into other growth, such as height or lateral branches."
Therefore, while the diameter of a tree can be one factor in estimating its age, it should be used in conjunction with other methods such as counting growth rings and examining surrounding forest characteristics.
I find what Mr. Van Pelt has to say about the appearance of the crowns of Western Redcedar to be a significant factor in determining age. According to Mr. Van Pelt:
"Very old Western Redcedars often have a unique appearance, with a broad, flattened crown that may resemble a platform or table. This is because the upper branches of the tree have spread out horizontally over time, and the tree has also shed lower branches, creating a flat or concave top. The size and shape of the crown can provide some clues about the age and health of the tree."
“Western Redcedar has highly decay-resistant wood. It is thus unlike its common associates Sitka spruce or western hemlock, in that it can survive major crown damage. When the top of a spruce or hemlock is blown out, the tree will often be unable to outgrow the incipient decay. A redcedar, in contrast, will resprout new leaders and continue on.
Top die-back is common on redcedar in particularly hot, dry summers. After the die-back, a new leader (or leaders) will develop from an existing branch (or branches) below the dead top. The dead leader often will remain on the tree after this recovery, so that after many centuries of this process, many of these dead tops will be present – giving rise to the term candelabra top. In many other trees, top dieback followed by reiteration from a side branch also occurs, but with different results. In a hemlock or a spruce, for example, the dead top will rot and fall away, so that after several decades the only evidence of the disturbance will be a slight kink in the trunk at the location of the re-sprout. The redcedar preserves its history of die-back and re-sprouting, so an ancient tree is a living record of its past.”
Thank you, Mr. Van Pelt.