Ewriting Format by Carl Peterson © 2002

Outline

I. History of the science of dendrochronology.
A. Early pioneer observations, Andrew Douglas, and archeology
B. Introduction of computers to solve tree ring problems

II. Dendrochronology tells us: "How does a tree grow?"
A. Earlywood vs. latewood
B. Events -fire -drought.
C. Recovery from injury
D. How are tree rings dated?

III. Nature's Ideal Forest
A. Include fire -exclude bugs
B. Include nature -exclude exploitation
C. Include forest ecologists -exclude politicos

Forest Ecology
A Forum at First Universalist Church of Denver
26 October 2003
Abstract. Dendrochronology is defined as "the dating of events by tree rings."
This relatively new science gives us the history of forest ecosystems in which natural events and human interference have taken place. In each tree the growth, injury, flood or drought is evidenced by tree rings. Ecologists therefore know what an ideal "natural" forest should be. The present administration is touting an approach to forest ecology that
is mistaken and could lead to disaster in our nations forests.

Further Interests
Forest specimens: Take a few moments to examine our tree ring collection. After our discussion, please ask any questions you may have regarding dendrochronology and
forest ecology. Note the dates of historic events on some specimens. Can you find your birth date? Your grandparents?
Copies of a paper, "Fire Ecology" written for participants in a field trip with the
Denver Museum of Nature and Science is available.
Also available are copies of the framed explanation of tree rings that hangs in the our office hallway. This is in conjunction with the samples of tree rings in each of our recent Christmas trees at First Universalist Church.
Recent talks given by Richard Kerr on forest ecology and dendrochronology:
The National Kitchen and Bath Association: "From Forest to Kitchen":
Why does the appearance wood differ from species to species?
Student class at the Denver Museum of Nature and Science.
Student class at Metropolitan State College of Denver

FIRE ECOLOGY AND DENDROCHRONOLOGY DENVER MUSEUM OF NATURE AND SCIENCE
Dendrochronology is the science of dating events by tree rings. It was first used effectively by the astronomer Andrew Douglas. He accurately dated early Native American settlements in Arizona. A new science early in the 2Oth century, dendrochronology grew in importance after computers were built that could process complex multivariate statistics. The science is now used to study many aspects of ecology, with our particular interest today being woodland wildfire.
Climatic variations from year to year are reflected in tree ring widths. A year with sufficient precipitation and comfortable temperatures produces larger-than-average ring widths. Too little precipitation and low temperatures produce smaller-than-average, ring widths. Distinctive patterns of wide and narrow rings allow the dendroclimatologist to reconstruct climate over millennia. A dendrochronologist can use the patterns to accurately date events, such as wildland fire, insect infestation, and seismic events. Tools of the trade for this exacting study are corers, microscopes, dental probes, and computers. A fire ecologist, using dendrochronology, first surveys the forest. Visible indications of repeated wildland fire are typically ground-level "catface" scars. These are normally found on the uphill-side of trees. Fire travels rapidly uphill. Encountering a tree, it quickly swirls around the trunk, burning forest litter that collected on the uphill side. Pinecones, leaves, and fallen branches roll downhill to be caught by the uphill side of a trunk. As the fire reaches this pile of forest debris, a very hot miniature tornado or "fire whorl" forms. This often burns through thick, protective bark and injures the "cambium," or outermost layer of growing cells. The downhill side of the tree is not injured. It has not collected any debris, since any excess rolled away downhill.
After fire passes, a tree starts recovering from the injury in several ways. It floods injured areas with sap to prevent insects and molds from entering the tree, much like a scab forming over your scraped elbow. The area will form a "false heartwood," appearing much like the darker heartwood in older trees. By-products of photosynthesis block the phloem and xylem --tubes that transport water and nutrients in tree trunks. Tendrils, or "arms," of molds are prevented from invading the entire tree along these passages. Mold that would eventually kill the tree is stopped by this "compartmentalization." One additional defense takes the longest time of these processes. Trees attempt to grow rings to cover an injured area, forming a "catface fire scar." Scars on surviving trees may indicate the passage of multiple wildfires over long periods of time.
Redwoods and ponderosa pines, for instance, are particularly well fire-adapted. Repeated, cool-burning, slow-moving ground fires do relatively little damage. These trees evolved over millennia a very thick, insulating bark. Periodic burning of
"understory" -- grass, brush, and smaller trees --returns nutrients to the ground and reduces competition for water and nutrients. Larger fire-adapted trees benefit. Early pioneers riding horseback through ponderosa forests of Northern Arizona reported ideal conditions in these lovely woodlands. Ten to fifteen feet in diameter, trees were separated by thirty to fifty yards of grass and pine needles. Repeated, low-level fires maintained a healthy forest. This ideal situation slows or avoids the effects of stand- destroying crown fires and insect infestation.

Today mismanagement has turned these fonnerly ideal forests into landscape so densely packed that one cannot walk between the crowded trees. Foresters call this a "dog hair thicket." Walk through this forest and you will know how a flea feels as it traverses hair on a dog! How have these forest conditions changed from ideal to poor? Simple: "Fight all fires to save all trees at all cost. Fire is evil and trees are good."
Ooooops! We left out something --what nature intended --periodic fire manicures the forest, maintains species distribution, and controls bugs! All fire-adapted vegetation has its own "fire return period" -- it will burn as soon as sufficient fuel has collected and the inevitable lightning strike starts a blaze. Nature intended fire to maintain forests. If fire is suppressed year after year, eventually there will be an unstoppable conflagration, much to the dismay of forest managers and people who love to live among tall trees.
Natural forests have a "fire mosaic" that forms over generations. This allows fire to clear away forest debris and crowded understory a few acres at a time. In northern. Baja California, the San Pedro Martir Mountains are not developed. Lack of roads makes effective fire fighting virtually impossible. When lightning strikes, a small area burns --.perhaps 1 to 100 acres --until the fire stops where it has burned recently. A fire mosaic results. This controls pests and lessens the chances of a disastrous crown fire.
Contrary to living with a healthy fire mosaic, crowded Southern California must fight all fires, as population pressure has pushed homes into the normal paths of wildland fire. Rather than a few acres burning in a mosaic, thousands of acres burn along with homes and businesses. Valuable recreational areas and watershed are lost. Unfortunately, nature intended periodic fire to maintain wildlands but, here fire creates human and economic disasters of gigantic proportions.
Must we prevent people from building homes in periodically burned wildland? It's difficult choice. The summer of 2002 saw a disaster in Colorado with hundreds of homes destroyed by wildfire. Many of us want to live in gorgeous woodland. The mountains of Colorado and ocean views from Southern California's coastal mountains beckon. Forest managers must come up with acceptable solutions to this difficult problem.
Controlled burns and mechanical removal of forest understory and debris are both effective but expensive answers. Moneyed timber interests would like to thin the forests, but prefer the fast cash of large trees. If they could be persuaded to take the smaller trees for "manufactured" wood, the forest would soon return to nature's preference.
Should homes be absolutely fire proof? It is very difficult to fire-proof a log cabin in the woods! A hot fire burning only fifty feet away can set cabin curtains afire --by radiant heat alone! In a dry, overgrown forest, winds spread flames faster than an Olympic runner can sprint. Wind-born flaming brands can leap miles ahead of afire to create isolated, explosive spot fires. Firefighting is impossible and woodland homes are destroyed. The final answer is infinitely complex.

BIOCHEMISTRY OF THE AUTUMN COLORS
What conditions are required to maximize the bright colors?
1. A growing season in which trees receive plenty of water and nutrients. A warm, rainy summer is best.
2. In the autumn, as the sun moves south after the solstice, temperatures lower and days become shorter. Trees sense the temperature change and shortened photoperiod and start preparing for winter .
3. Trees begin the process of moving nutrients from the leaves to be stored in the trunk and roots where they are safe from winter's cold.
4. Temperatures dip toward freezing but do NOT freeze. This is the signal for the trees to get really busy to store the nutrients. A cork layer grows over the base of each leaf, trapping the left-over nutrients in the leaves.
The chemicals that are left in the leaves start the display of autumn colors.
What colors are these chemicals?
1. GREEN: During the year, chlorophyll is the most visible color. It is chlorophyll that allows trees to process sunlight and carbon dioxide into hydrocarbons. These are the nutrients the trees require for growth.
2. YELLOW: Carotinoids are in the leaf all year, but only become visible when the chlorophyll is reduced. These vary from bright yellow to deep gold and are the chemicals that make carrots --carrot color!
3. RED: As the cork layer in each leaf grows, it traps some of the sugars that have formed in the leaf. The excess sugars create anthocyanins. These chemicals are responsible for several colors ranging from bright red to
dark purple. Often these colors are enhanced by the other chemicals.
4. BROWN : When your parents have a cup of tea or coffee for breakfast, they are drinking tannins, which become tannic acid! Tannins are the color in fallen leaves, tea and coffee! Tannic acid as a medicine may be used to treat a mild burn. You may have heard about people putting tea leaves --tannic acid --on a bum. Your leather shoes are tan because they are tanned (i.e. cured) with tannic acid!
What happens to all these chemicals? Most are stored in the tree and roots until the next growing season. The remaining brown tannins and other parts of the dead, rotting leaves become fertilizer for the tree and surrounding vegetation. If the forest floor burns, this hastens the nutrients into the ground to be used by the tree.

Beautiful Tree Rings!
Each year trees form a new growth ring. We can count the rings and tell the tree's age. We can also tell when something happened to the tree --perhaps it survived a forest fire. The science of dating events by tree rings is called Dendrochronology
In the spring a tree grows new cells in the cambium --the outermost layer of living cells. This "earlywood" is light colored and becomes part of the annual ring. Late in the year the tree grows a darker layer. This "latewood" forms the last part of the ring for that year. Therefore one annual ring is made up of a light and a dark layer. By measuring the width of each ring a dendrochronologist can tell if that year was a good growing year. The wider the ring, the better the growing year. A narrow ring tells us "drought!". The drought years of 2002 and 2003 will show up as very narrow rings because the trees have not had enough water. The forest fires of 2002 injured many trees. The ones that survive may show a "fire scar." Many years from now this will tell us exactly when that fire burned. Some trees show a series of forest fires over many years. Tree rings can also tell us when the forest had an infestation of insects that injured the trees. Many different events in human history may be dated by tree rings.

Happy Tree Ring counting!
Richard T. Kerr
Dendrochronologist and Member,
First Universalist Church of Denver

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