The Life of a Nurse Log

Do you see anything unusual about the trees in the photo above? If you noticed that they are growing in what looks like an unnaturally straight row, and that their roots seem to extend rather high up their trunks, you are on the right track.

This is known as a "colonnade" (a row of columns) that has grown from a "nurse log". These are common in temperate rain forests like the Hoh Rain Forest in Olympic National Park, where I took this photo. These are Western Hemlocks and Sitka Spruces, which are the most common trees in the Hoh Rain Forest.

As we walked through the forest that day we came across many other nurse logs. I thought it would be interesting to put these photos in order of their stages of growth, so you can see the full life cycle of a nurse log.

Sometime after a tree dies, it will come crashing to the forest floor. Unless it is a relatively young and small tree, it is probably not going to fall from the same force that caused it to die (for instance, a lightning strike or a storm). More than likely it will die from a number of factors acting on it over the years, and it will probably remain standing as a "snag" for many years after it is completely dead. During this time, it will likely host many small mammals, birds and insects. But when its roots finally decay to the point where they can no longer support the tree ... CRASH!

As the tree dies and falls, it opens up an area of sunlight in the forest. The leaves of the tree itself no longer block sunlight from reaching the forest floor, plus smaller trees and some branches of other large trees are smashed on the way down.

After a few years, the fallen tree will be decayed by fungus, microbes and insects to the point where its surface resembles soil (humus). Now all we need are some seeds to fall on the log. They have a perfect place to grow - rich organic soil, a newly created patch of sunlight, and a platform to raise them above the undergrowth they would otherwise be competing with.

Here we are a little while later, with a top view of a log that has really started growing.

And here is a young tree that has clearly taken hold and will be the dominant "nursling" on this part of the log.

Fast forward a few years, and here is a well established tree. At the front of the nurse log, you can see some of the roots the new tree has sent to the deeper soil under the log.

And several more years after that ...

Eventually the new trees start getting bigger than the nurse log, and the nurse log decays to the point where it loses its definition.

Finally the nurse log is completely gone, nothing more than a "ghost log" of twisted roots that were once around and through the nurse log.

And here is what can happen if a tree falls and leaves its stump in the ground, such as from a lightning strike or a chain saw. I guess you would call this a "ghost stump".

The roots of some trees eventually grow in a way that makes them look like they are on stilts, in bizarre shapes with large open areas where their nurse logs once were.


As you can probably guess, after these trees live a long and full life, they will someday become nurse logs themselves for a new generation of trees. This is a very long cycle. Western Hemlocks and Sitka Spruces can live over 500 years, not counting their "second life" as a snag and then a nurse log. Some of the oldest trees in this forest were "nursing" at the same time Christopher Columbus was nursing!

Uncompahgre Fritillary

I recently read Halfway to Heaven by Mark Obmascik. It is about a balding, overweight dad trying to achieve a mid-life goal. Not that I would know anything about that. I would consider myself closer to bald than balding. And although Obmascik refers to himself as overweight many times, my guess is that the photo on the cover flap was taken after he achieved his goal - of climbing all 54 of Colorado’s 14,000 foot mountains within one year. That makes my goal of becoming rich and famous seem easy!

As Obmascik progresses - some climbs easy, some hard, some exposing his insanity - he tells stories about himself and the mountains. One of my favorite stories was about the Uncompahgre Fritillary. This small, orange and brown butterfly was named after Uncompahgre Peak, where it was first discovered by modern scientists in 1978.

The Uncompahgre Fritillary has one the smallest ranges of any North American butterfly. It is found only on northeast-facing slopes of the San Juan Mountain range in Colorado, at elevations above 12,500 feet, near the snow willow plants that their caterpillars eat. It is an endangered species, with only 11 known populations containing a total of a few thousand individuals.

Obmascik doesn’t admit to actually seeing any of these rare insects himself, only to coming across a grad student who was out looking for them. They were both making a hasty retreat from a violent thunderstorm on Redcloud Peak, home of the largest population of Uncompahgres. The grad student was carrying some type of recording or communication device with a tall metal antenna, so Obmascik was happy to have him draw the lighting away from him.

The Uncompahgre is believed to be a holdout from the last Ice Age, when they and their favored habitat were much more abundant than today. As the glaciers retreated, the butterfly's range shrunk and moved upward in elevation. Global warming is one of the many stresses affecting this butterfly's survival. At this point, they only have about 2000 ft more to move up before they run out of mountain. Let's hope that this creature which has survived since the Ice Age, and was only discovered in 1978, does not get forced into extinction.

Sorry for the blurry photo, that's the best one I could find in the public domain (from the US Fish & Wildlife Service).

Post Office Advances Marine Science

This cool old map was drawn up by the Post Office in their never-ending effort to deliver our mail through snow and rain and heat and gloom of night. It is the first known map of the Gulf Stream current, and it was created by Benjamin Franklin, then Deputy Postmaster General of North America.

The problem that prompted Franklin to make this map was complaints of poor postal service (some things never change). Postal customers in England found that letters they sent to the colonies took much longer to arrive than letters sent the other direction. Even when two ships, a postal ship (called a "packet ship") and a merchant ship, left England at the same time, the merchant ship always arrived first. Surely the letter carriers were lollygagging?

Franklin looked into this customer complaint with his usual scientific curiosity. Having crossed the pond himself before, he knew that certain parts of it contained "gulph weed", a type of seaweed that grows in tropical waters. He had also noticed the eastward flow of this current, and called it the "gulph stream".

Franklin suspected that this "gulph stream" was the reason for his postal problems. But first he consulted with an expert, his cousin Timothy Folger who was captain of a whaling ship. Folger explained that whaling ships often followed the gulph stream, because whales liked to eat the plankton that flourished in it. And he could attest to the fact that the gulph stream moved like a river within the ocean, noticeably quicker than the water on either side.

With Folger's assistance, Franklin drew the first map of the Gulf Stream. On later trips across the Atlantic, as full Postmaster General, Franklin measured the temperature of the water. He found the water to be warmer within the Gulf Stream, and noticed that it did not sparkle at night like the colder water on either side.

Before Franklin's map, some mariners knew about the Gulf Stream and others didn't. This knowledge was a valuable competitive advantage, not something to share with the world like Franklin the scientist wanted to do. But even Franklin eventually realized the value of this information, and stopped distributing the map in England during the Revolution. He instead made sure it got into the hands of the French sea captains who were supplying the Americans.

I learned about this interesting intersection of science, commerce and war in the book The Invention of Air by Steven Johnson. This book is about Joseph Priestley, and includes a lot about his close friend and mentor Ben Franklin. Priestley later replicated Franklin's measurements of the Gulf Stream.

Now, if the Post Office could just do something about those long lines to ship a package ...

The Evolution of Air

I recently read The Invention of Air by Steven Johnson. It is about Joseph Priestley and the Enlightenment movement that he was part of in England and America.

Joseph Priestley is the man who is commonly credited with discovering oxygen. Unfortunately Priestley was neither the first to isolate oxygen (that was Carl Scheele), the first to understand its true nature (Antoine Lavoisier), nor the one to give it the name we use today (Lavoisier again). Priestley was the first to publish the fact that he had isolated oxygen, and he was already well known for other pursuits, so his is the name we usually associate with oxygen.

But what I really want to know is - what the heck does the title of the book mean?

Obviously, no one including our hero Priestley "invented" air. The title must be a metaphor. I went to engineering school, so I won't be much help with the metaphors.

According to one of the reviewers quoted at the front of the book, who was clearly a literature major, the "invention of air" refers to "how groups of scientists, natural philosophers, religious leaders, and politicians served as cultural petri dishes in which ideas were discussed, experimented with, discarded, or accepted".

This is definitely one of the themes of the book. But using the K.I.S.S. principle of metaphor interpretation, I noticed that the few times the author actually used the word "invent" in the book, he was referring to evolution - as in 'Mother Nature invented this', or 'plants invented that'.

Supporting my simplistic decoding of the title is the fact that the author stresses the one thing Priestley unequivocally did discover - that whatever it was plants breathed out, animals breathed in. Priestley was the father of ecosystem science. For this he received the Copley Medal, the Nobel Prize of his day. The presenter of this award in 1773 could have been making a presentation today on "ecosystem services":

From these discoveries we are assured, that no vegetable grows in vain, but that from the oak of the forest to the grass of the field, every individual plant is serviceable to mankind.

So where does evolution come in? The author explains that when our Earth came into being, its atmosphere did not contain any oxygen. Some of the earliest life forms, cyanobacteria, evolved to use what they had available to them - water, sunlight and carbon dioxide. Their waste product, oxygen, was deadly to the other (anaerobic) microorganisms they were battling for world dominance. Great plan!

It would be millions of years before plants evolved that could make use of some of this waste oxygen, along with the water, sunlight and carbon dioxide, and produce even more waste oxygen. (Yes, plants do use oxygen for respiration. But since they produce more oxygen through photosynthesis than they use for respiration, we don't think of them as using oxygen too.)

It would be millions more years before animals evolved that would finally use up some of this waste oxygen. Before atmospheric oxygen levels settled into equilibrium at today's 21%, they climbed as high as 35%. This created some huge plants and animals in the Carboniferous period - mosses 130 feet tall, dragonflies with a wingspan of 2 1/2 feet, and millipedes 8 feet long.

Here's the 8 foot millipede (Arthropleura), advertising BBC's show Walking With Monsters. I'm sure glad I missed the Carboniferous.