Sunday, October 26, 2014

Jane Austen and wildfire?

Interesting stream of thought after returning from the 2014 annual meeting of the Geological Society of America: was relaxing at home late Thursday afternoon and caught the end of one of my favorite movies, the rather esoteric chick flick, The Jane Austen Book Club. Set in California and filmed in southern California, their last book club meeting, discussing Persuasion, was at a rocky beach, typical of many along the Pacific US coast. Besides the intensely deep blue color of Pacific water, these beaches descending from the rugged coastline are different from the wide sandy beaches I have lived near most of my life on the US Atlantic passive-margin coastal plain from New York south to Florida.

I was reminded of beaches like this in Oregon, with Haystack Hill, which was one my husband and I stopped at while driving down Pacific coastal highways from Seattle to Los Angeles in 2012.
The Oregon beach, like several others we saw, was pebbly, like the movie's 'Persuasion' beach; this Oregon one was so consistent in pebble size and color, I used it as my iPhone home screen wallpaper for a while. But thinking about that beach, led me mentally to the coastal redwood state and national parks we visited farther south in northern California during that trip.
I was fascinated by the not infrequent fire scarring on the redwoods, here from Jedediah Smith Redwoods State Park ( I was intrigued enough to take several burn scar photos). Redwoods can survive ground fires, even with obvious burning, although decay associated with scars can be a problem in recovery.
A number of trees have these fire cavities. A good explanation of these can be found at http://www.redwood.forestthreats.org/cavities.htm. Once fire starts burning the more resistant sapwood inside, fire temperature and intensity can increase and seriously threaten survival of the tree. The Coast Redwood Ecology and Management website, a consortium of private institutions and government agencies, also has case studies of individual modern fires among redwoods (http://www.redwood.forestthreats.org/canoe.htm)

Giant redwoods, a coastal tree, are a different species from the giant sequoia, which are also only found in California but at higher inland elevations. A number of studies of fire history and sequoia have been done by Thomas Swetnam (including "Fire history and climate change in giant sequoia groves" Science, v. 262, 1993), who has collaborated with, among others, Andrew Scott, mentioned in previous blogs.

In coals and organic-bearing sediments, examples of the incomplete burning of wood during wildfires millions of years ago can also be found. Under the microscope, particles are occasionally seen that show the transition from very burned to less charred wood. Fusinite, a highly reflecting inertinite maceral (see first blog entry) frequently showing the skeletal structure of charred wood or charcoal, may visibly transition to semi-fusinite, a less-reflecting maceral, but possibly still having a porous skeletal structure. Rarely, vitrinite, the maceral of uncombusted wood, may even be present showing a complete sequence from charred to unaffected.


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