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Image 1: A wedge about to be removed from a fire-scarred western redcedar tree. Tree rings are used to reconstruct drought years and fire events (Photo: Kira Hoffman). Image 2: The forests of Hecate Island located in the Great Bear Rainforest on the central coast of British Columbia (Photo: Kira Hoffman). Image 3: Kira Hoffman extracts a core sample from a western redcedar tree (photo: Malcolm Johnson). Image 4: Wide rings infer favourable growing years (warm and wet) and tight rings indicate stressful growing conditions such as drought or prolonged cool temperatures (Photo: Kira Hoffman). "One Ring to Bind Them All" By Kira Hoffman A dendrochronologist counts her millionth tree rings, and nothing happens…or does it? The clock ticks as I click my mouse and stare at the computer screen. A warm breeze blows through the University of Victoria Tree Ring Lab, and it’s incredibly quiet save for the constant beep of the Velmex machine and the whirring sounds of a flatbed scanner readying tree cores for analysis. It’s a hot Friday afternoon in August, and the campus is empty. There have been many days and months like this since I set out to measure 4200 tree cores for my Doctoral dissertation on forest ecology. But today is a day like no other—it’s the day I will measure my millionth tree ring. And little by little, 1200 years of chronicled events recorded on western redcedar trees from British Columbia’s coastal temperate rainforest will become clearer. Dendrochronology is the science of tree rings and tree ring sequences. With each ring showing a specific year’s growth, it’s not just the rings themselves that are special, but also the monumental life span of rainforest species and their ability to record major climate and disturbance events. In this part of the world, large rings indicate good growing years with moderate conditions; tight rings chronicle insect outbreaks, years with extreme weather or droughts associated with El Nino cycles. Fire scars, also present within the rings, show low-intensity ground fires that injured, but did not kill, the trees. The trees are sampled with an increment borer, which removes five millimetre cylindrical cores from the trees and resembles a large corkscrew. The trees whose rings I’m counting grow on British Columbia’s Central Coast, an area that contains one of the largest remaining intact temperate rainforests in the world. Despite looking like untouched woodland, forests here have been managed by Indigenous Peoples since time immemorial. Western redcedar, also known as the tree of life, provided people with shelter, clothing, tools and transportation. People managed their forests like gardens through selective harvesting, fertilizing and controlled burning, and that long-term relationship is recorded like an annual calendar on trees that still live today. The ability to go back in time, and the potential of these trees to provide an understanding of the past, is constantly on my mind as I measure and record each ring. I suspect other researchers have shared my feelings of wonder, doubt and frustration as they’ve tried to fit, match and decipher the puzzle that is dendrochronology. The scientific quest can be lonely at times, but I take comfort in the relationships I’ve established with fellow ecologists and dendrochronologists around the world who are asking similar questions and striving to understand the past. I am using tree cores to reconstruct what the coastal forests would have looked like hundreds of years ago and to understand how, why and when people used fire to manage forests. The Velmex, a microscope designed to count and measure trees, beeps for the millionth time. I stop and lean back in my all-too-familiar swivel chair—after three years of studies, I’ve measured one million rings and one million years of growth. The lucky ring dates from the year 1656, embedded in the middle of a tree standing five feet tall in a bog woodland on Hecate Island. I take a moment to think of all the things I’ve learned from these trees—like the fact that big trees are often the youngest, while small trees gnarled by storms and perched on sphagnum hummocks are often the oldest, or that a tree can tell you the exact years and months that people were managing the land with fire. I click ahead: One million and one. And then I laugh, because no one comes into the room with a bottle of champagne and a medal. Over the years, I’d heard whispers of a secret society of million ringers at dendrochronology conferences, and I’d seen blog posts questioning who really was the Lord of the Tree Rings. I click ahead again: One million and two. Maybe the Velmex beeps do sound a little different—or maybe it’s the knowledge that in the world of dendrochronology, I’ve officially become a member of the fellowship of the rings.
Posted 22 September 2016