Sunday, July 26, 2009

Something I’ve Pondered

Why do some trees exhibit thin exfoliating bark while most trees have durable, rigid, fissured bark?



Texas Madrone (Arbutus xalapensis).



For me it was a discovery, my first ever look at this beautiful red bark tree. The bark so smooth to touch, the leaves a deep green. I learned that it’s evergreen, it flowers and it fruits and sheds it bark twice a year. In 1972 the TOES, the Texas Organization for Endangered Species, designated it as rare and endangered. I became very interested in the “Naked Indian” as the Texas Madrone is frequently called. I’m told that Blanco County has the largest number of these trees in the Texas Hill Country.



Photograph taken by J. David.



From an apparently dead trunk or limb, life had continued by growing around the dead limb like a snake and shooting off the dead trunk to form a new alive limb or branch. I noticed that the strength wasn’t there and later on I found these mortally wounded and broken by the wind.



Photograph taken by J. David.



As the restoration of the ranch progressed, we found many Madrones growing within cedar thickets. Some were big up to 20 feet; others small, growing in close to the cedar trunk which protected it from browsing deer or goats. Some believe there is a symbiotic relationship between Cedars and Madrones. I believe it’s only the protection the cedar provided. The dead cedar limb is coveted as a stave for fence building because it’s all heart and very strong. It’s much better than the metal stave sold today which bends when pushed on by cattle and deer and disfigures a perfectly good fence. But back to my experience with the Madrone:


We were so very busy and preoccupied in those early days with the restoration work that other than asking Leroy to tag and avoid any Madrones, they didn’t get my attention. Then one day in May when I was assessing our restoration progress, I was shocked to see something terribly wrong with a big old Madrone. My heart nearly stopped! The foliage looked skimpy, the tree somewhat bare. Had we injured her with the dozer? The ground was littered with sickly looking green and brown leaves. However upon examination my anxiety was relieved. The leaves had been pushed off, shed by nature and many small new leaves were beginning to grow and on the end of some twigs little green berries with red cheeks were forming.



Photographs taken by J. David.



It was the end of June that I made my next visit to the Madrone. This is when I first witnessed the tree shedding its bark ~ the scientists call it exfoliating. It was such a surprise, a dramatic change more like a chameleon or snake than a tree. I’d never witnessed this before! From the trunk base to the tips of each limb and branch, it was shedding its beautiful red bark. Large chunks of bark that looked more like parchment hung from the bigger limbs. The ground was littered with it. It was peeling and curling back from the limbs to reveal a new coat. Now, this thin bark was a white, light brown where it was most exposed to the sun and a kind of pale green under the flap of the peeling bark. . . .


There are many more notations in my journal about the Texas Madrone, but I’ve been told my blog is too long and people won’t take time to read it. “A word to the wise is sufficient,” the philosopher said. So back to the question – Why does the bark peel on the Texas Madrone? I didn’t get an answer from the many books in our ranch library so I began asking people who should know, Ph. D.’s, botanists, horticulturists and forest management people. It was interesting, their responses. Oh, how I’d like to list their names and professional qualifications, you’d be surprised and they’d be embarrassed!


“You raise an interesting question. I do not have an answer. I would venture that the trees that exhibit thin exfoliating bark have been able to survive and reproduce apparently without the need of the normal dense protective bark that most trees produce. It may be possible that thin bark even enhances the chances for survival of these species in some manner. Perhaps their sap or inner bark is disagreeable to most insects and animals. It is rare to see a thin bark tree showing evidence of being attacked.


It would at first observation seem to put them at a disadvantage as to gnawing animals, exposure to fire and general physical and thermal protection. It is an interesting question that I can not answer.” - from a Texas A&M graduate with an urban forestry degree and twenty–five years field experience “Good question. I honestly don’t know the physiology of that. Normally bark is just shed periodically as the cambium layer under the bark grows, expanding outwards and then some trees just get really gnarled, thick, compact fissured bark that never really shed or peel, while others exfoliate regularly. Why some trees would do this twice in the season must have something to do with their annual growth cycle for the cambium layer, but again, I am not sure of the exact physiology or environmental response reason behind this.” – from a Professor of Natural History


“Thin bark trees do not grow in cold climates. They didn’t need the protective bark probably where fire didn’t go. How they got away with it, not being chewed upon, I don’t know.” – from a Forest Service Biologist


Exfoliation – as the stem grows the bark tightens and stretches back until it splits, kind of like a snake skin. On other trees the bark is vertical.” – from a High Level Forest Service Biologist


“I’ve never been asked that question. I have no idea.” – from a Horticulturist


“This tree has thin bark that cannot expand to accommodate new growth. The peeling bark is a result.” – from a Park Naturalist


Well, there you have it from the experts; but you don’t have it, as there is no consensus and no research on the subject. As for me, I just appreciate the Madrone as I do all of nature’s treasures. I know there are 47 Texas Madrones, in different stages of their life around Madrone Lake. I think I’ll count all the others this fall when it’s a bit cooler.

5 comments:

Mikael Behrens said...

Thanks for such an interesting post! I took an ecotourism trip to Ecuador a few years ago. In the dense rain forests there most trees were covered with all kinds of mosses, epiphytes, parasites, and other things. But certain trees stood out as clean and free of this layer of growths. These were trees that periodically shed their bark. And our guide told us that was the reason; along with their bark, they shed everything that was currently trying to live on the bark and grow deeper into the tree.

Could this be why the Madrone sheds its bark too?

Sallie said...

Great lesson on an amazing tree. Thanks. I don't think your posts are too long!

Charles said...

J. David,
Your comments may be too long for some as a blog, but NOT as "J. David's Journal". Some of us look forward to your next journal entry, and it's not too long for anyone interested in learning what you have to offer.
By the way, it appears the Texas Persimmon has the same type of bark. I have several of them on my property, but I haven't really observed when they shed or how frequently.
Keep up the good work and don't be concerned about the length of the journal entry!
Chuck

selah said...

The only other hypothesis I've heard about the peeling of the bark was about solar heat. If the Madrone peels the darker red in the summer, could it be cooler for it to survive with its lighter colored bark and then go back to the darker red when the climate turns colder? This hypothesis, however, wouldn't make sense if you posed the question to the persimmon or even crepe mertle. Leave it to JDavid to always ask teh good questions!!

Ryan Kingsbery said...

Great blogs David! Always good to read them and see what's going on at the ranch! You know, you should write a blog about the 'company car'!