Thursday, June 18, 2015

Muir Woods a Mere 777 Years Old

Muir Woods is a coastal redwood forest that was designated a national monument in 1908. Muir Woods is located 12 miles north of San Francisco in Marin County in Redwood Canyon two miles inland from the Pacific Ocean. The canyon forms a wetter and cooler micro climate with the moisture from the heavy summer fogs that roll in from the Pacific provide the moisture that has allowed the Coastal Redwoods to grow.

The woods is a beautiful place; silent and majestic on an early spring week day when most tourists are home. It is a place I dragged all my relatives to walk in the woods, picnic and hug a tree when they visited us in San Francisco. Sometimes I would go to the woods to hike the trails and just be alone. I walked the pathway and read the placards several times a year until I knew by heart that the oldest and largest tree in Muir Woods was believed to be more than 1,500 years old. That turns out not to be true.

The age of trees is determined by the counting of tree rings. The science of studying tree ring patterns is called dendrochronology and was created by A.E. Douglas at the beginning of the 20th century. In 1922 he used the methods to date the Giant Sequoias (cousins to the coastal redwoods). In general, each year a tree is alive and grows is marked by a growth ring; the tree gains a little bit of girth though there can be years where rings are absent. The width of the ring added to the outside of the tree is in part dependent on the amount of moisture available to the tree thus trees in the same area add thin rings during dry years and thick rings during wet years. In this way, by examining the rings of a group of trees, the scientists can study the history of the climate and weather in a region.

Researchers from Humboldt State University, University of California at Berkeley and Natureserve were studying the impacts of climate change on redwood growth, carbon storage and forest biodiversity through the Redwoods and Climate Change Initiative (RCCI) one of the many climate change impact funded studies. As part of the study scientists took pencil-thin cross sections from trees to count their growth rings. As mentioned, tree rings vary in width and tell a story of the tree’s growth history and what was happening in the forest during a particular year. Together the tree rings over a region form a catalogue of regional climate.

When Allyson Carroll of Humboldt State University analyzed the data she found that the oldest tree in Muir Woods, the giant 249 foot tall “Tree 76”, is not some 1,500 years old as previously assumed, but a mere 777 years old. The samples were taken in March of 2014 and I was surprised to hear represent the first significant scientific study of the tree canopy at Muir Woods. Besides Tree 76, Ms. Carroll determined the ages of two fallen trees in the forest; the Vortex Tree was 693 years old, and the Solstice Tree, was 536 years old. This leads to the theory that the entire grove is probably younger than previously thought.
From Allyson Carroll Presentation

The new theory of Muir Woods is that some catastrophe likely struck the area; a fire perhaps suggested by burn record, forcing the forest to start again from scratch. Scientists will attempt to use the reconstruction of the past climate to learn how redwoods have responded historically to climate change and assess how the trees are adapting currently.
The Ward Cousins Hugging a Redwood Tree

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