Tree ring age dating
Molecular biology offers some insights into why the ability to make wood is maintained and reappears so often in plant evolution.
Genes that are involved in regulating the growing shoot — the upward, “primary” growth of trees and non-trees alike — are also active during the secondary growth that yields wood.
It seems to evolve fairly quickly after plants colonize islands.
Hawaii, for example, has woody violets, and the Canary Islands have dandelion trees.
After this cellular stiffening, the wood cells are killed and dismantled, for the most part, until nothing but their rigid walls remain.
In plants that exist today, secondary growth probably had a single evolutionary origin, although the now-diminutive club mosses and horsetails invented their own version some 300 million years ago, enabling the extinct , for example, to grow more than 100 feet tall.
“Visit your favorite plant nursery and you will find plants categorized by their appearance and function, including a group categorized as ‘trees’,” he writes in a 2005 paper in , “What genes make a tree a tree?
He is quick to acknowledge that defining them is problematic.
Sometimes it results from a tragic human blunder, as with the 3,500-year-old Florida bald cypress that was killed in 2012 by an intentionally lit fire.
More often, calamity strikes via extreme weather — drought, wind, fire or ice.
Several years ago, after Thanksgiving dinner at my parents’ house in Vermont, lightning struck a backyard maple tree.
There was a ferocious crack and the darkness outside the kitchen windows briefly turned day-bright.