Overstory #182 - Remember to touch trees
Since 1998, Dr. Alex L. Shigo has contributed four articles to The Overstory (editions 68, 69, 70, and 132). Earlier this month, Dr. Shigo passed away at the age of 75. Dr. Shigo led a revolution in the way we think about arboriculture. The following is a selection of passages from Dr. Shigo's prolific writings. See "About the Author" below for a brief biography of Dr. Shigo and for information about purchasing his publications.
from Tree Basics (p. 4)
A brief overview of some unique features of trees
Trees are the tallest, most massive, longest-lived organisms ever to grow on earth.
Trees, like other plants, cannot move. However, trees, unlike other plants, are big, woody, and perennial, which means they are easy targets for constant wounding.
Trees are super survivors mainly because they grow in ways that give them defense systems that are highly effective against infections from wounds.
Trees have the capacity to adjust rapidly to changes that threaten their survival.
Animals move to get food, water, and shelter. They move to avoid destructive agents. When animals are injured and infected, processes of restoration and repair start. Animals heal after wounding.
When trees are injured and infected, processes of boundary formation start. Trees do not restore or repair wood that is injured and infected. In this sense, trees do not heal. Instead, trees compartmentalize wound infections.
Compartmentalization is the tree's defense process after injuries where boundaries form that resist the spread of infections. The boundaries also protect systems involving water, air, energy storage, and mechanical support. In a sense, the boundaries are like an inside bark.
Tree Basics (p. 30)
Trees provide their associates with food, water, shelter, and home, nesting, and roosting sites.
Here are some of the benefits the associates provide for trees
- Facilitate absorption of water and elements - fungi, (mycorrhizae).
- Break down organic and inorganic materials - bacteria, fungi, nsects, animals.
- Aerate soils - worms, insects, fungi, animals.
- Fertilize - droppings from worms, insects, and other animals.
- Detoxify harmful substances - bacteria and fungi.
- Help adjust pH - bacteria, fungi.
- Convert nitrogen in air to a usable form (fix nitrogen) - bacteria and actinomycetes.
- Protect roots against pathogens - bacteria, fungi, (mycorrhizae).
- Hold water - actinomycetes, bacteria, (cell coatings).
- Regulate slow-release fertilizers - bacteria.
- Resist decay - anaerobic bacteria (wetwood), non-decay-causing fungi (discolored wood).
- Disseminate seeds - birds, animals, insects.
- Pollinate flowers - insects, animals, especially birds and bats.
- Facilitate branch shedding - rot-causing fungi.
- Protection against wound infection by decay-causing fungi - bacteria, non-decay-causing fungi.
from A New Tree Biology (p. 161)
Survival means to remain alive under conditions that have the potential to kill. Trees, as we know them today have been evolving on this earth for over 200 million years. They have survived the killing forces of countless pathogens and the ravages of environmental extremes. Somehow, some trees have remained alive under all types of conditions that had the potential to kill. But, trees did not accomplish this by acting as individuals. Trees connected or interacted with a great number of other living things, and together they survived. The power of interactions and connections kept many living things alive. Indeed, trees evolved in groups. They had group protection and group defense. They were protected and defended by their neighbors and associates, and trees protected and defended them. A tight circle or web of connections was the way the individuals within the group survived.
Now the connections are being broken. The heart of the survival system is being threatened. The most deadly words to the survival system are "suddenly and repeated." Given enough time most members of the large circle adapted to adverse conditions. But, when adverse conditions repeat faster than adaptation can occur, then the entire system is threatened.
Trees never knew a stump until axes and saws came into the forest. Trees never knew complete removal of trunks, machine compaction of soils, sudden changes in water drainage patterns due to roads, pollution, and disruption of niches for soil organisms. The list goes on. These actions have come suddenly. They are being repeated.
from A New Tree Biology (p. 458)
A hundred times, at least, I have heard it said, "....the client wants their trees topped, and we (the arborist talking) give them what they want and what they will pay for. We must make a profit, or we will not be in business long. And, believe me, the next company that comes along will take the topping job." A dilemma begins to happen. If the arborist does not do the requested topping, somebody else will and the trees still will be injured, so the first arborist often feels that he might as well do the injurious job and get the profit. Some arborists will refuse to top trees. I accept the fact that there is a dilemma. And, I believe that like wound dressings, topping will never go away, but I also believe that there are ways to greatly reduce this injurious practice and still make profit, or even more profit.
First, some order is needed on the subject. Let us not confuse topping-the internodal removal of a leader trunk - with early pruning or training of young trees, pollarding, bonsai pruning, crown reduction by cutting at crotches (many names for this drop crotch pruning, dehorning, etc.). Topping is done internodal; proper crown reduction is done at nodes, or at crotches. So the first separation must be nodes - good, internodes - bad.
from 5 minute Tree Care (p. 1)
For all people who care about trees, but do not have the time to read long articles.
CORRECT 5 simple primary tree problems and you will prevent many costly secondary problems caused by insects, diseases, heat and cold extremes, and drought. You will also reduce the chances of your trees becoming hazards.
Five major problems and their solutions
- SELECT HEALTHY TREES. Do not buy or plant trees that have roots crushed or crowded in a bag or container.
- PLANT PROPERLY Do not plant too deep.
- PLANT THE RIGHT TREE IN THE RIGHT PLACE. Do not plant large-maturing trees near buildings or power lines.
- PRUNE BRANCHES CORRECTLY. Do not remove branch collars or leave stubs.
- PRUNE TREES CORRECTLY. Do not top trees.
from Modern Aboriculture (p. xvi)
Modern arboriculture means
- The right tree in the right place.
- Building designs that give trees space to grow.
- Beautiful trees growing in clusters.
- Healthy trees growing below grade.
- Young trees with space to grow and with proper early pruning.
- The target is removed, not the tree.
- No sprouts from a correct pruning cut.
- Early training regulates size and shape of trees.
- The sidewalk is cut, not the tree or its roots.
- Proper care for old trees, and respect for their dignity.
- Planting trees at the proper depth.
- People touching trees and learning how they work, before they work on them.
- Treatments that destroy defense systems must be stopped.
- Treatments that cause serious internal injuries must be stopped.
- Treatments that start other problems must be stopped.
- Treatments that injure and kill transplanted trees must be stopped.
from A New Tree Biology Dictionary (p. 26)
Concentrations and survival
What keeps you alive, can kill you. No water or no salt will kill you, and too much water or too much salt will kill you. It is not water and salt that are essential for survival. It is the proper concentrations of each that are essential. Concentrations of all the factors essential for survival are always changing in nature. Constant adaptation is needed to survive in such an environment. The static state does not exist, and what may be good today could be bad tomorrow for a tree. A cavity full of water will be bad for the decay-causing organisms and good for the tree. As the water evaporates, a point of wood moisture will be reached that will be very good for the wood-decaying organisms. Then they will grow rapidly, within the boundaries set by the tree. When the moisture concentration falls below a certain level, the wood-decaying organisms do not grow further. Moisture, temperature, and all the essential elements are constantly changing, and conditions that are too extreme for best growth of the tree or the pathogens, are also always changing. Vibrations in concentrations of essential survival factors are ways natural systems constantly rid themselves of the weak individuals. We must be very careful not to disrupt the natural fluctuations by adding too much water, and too much fertilizer, or by disturbing the tree at a critical time in the vibration period. This is why we need to understand tree biology. Too many times our honest and loving attempts to help are really actions that hurt the plant.
from New Tree Health (p. 1)
TREES grow taller, live longer, and become more massive than any other living thing because trees are perennial woody plants.
WOOD gives trees superior mechanical support, which is the trees' unique feature.
ROT destroys the trees' unique feature.
PREVENT WOUNDS THAT LEAD TO ROT lawnmowers, cars, fire, construction, climbing spikes, improper pruning, topping, deep injection and implant holes, and the list goes on and on!
Shigo on Trees (back cover)
Trees have dignity, too.
There comes a time when trees in cities, parks, and near homes should be removed and new ones planted.
When possible, plant trees in groups or clusters.
LEARN about trees and their associates so that you can help make better decisions for their long-term, high-quality survival.
from Tree Hazards (p. 1)
A tree hurts, too!
Most tree hazards do not just happen. They are usually started by mistreatments by people. When a hazardous tree breaks, it may hurt not only people, but the tree hurts, too in the sense of wounds or even death.
MOST TREE HAZARDS CAN BE PREVENTED by regular checkups and proper treatments by tree professionals - arborists.
from Tree Hazards (p. 3)
CAUTION! Before more trees and people are injured and killed, we must STOP doing some old injurious tree practices and START doing some new beneficial ones. The list is long.
Here are a few examples
- Removing tops of upright leader stems on big trees - TOPPING.
- Removing tips of large branches on big trees - TIPPING.
- Removing branch collars when pruning- FLUSH CUTTING.
- Planting trees that grow big, under power lines or in small spaces.
- Planting trees that have many low branches with tight crotches.
- Wounding trees, especially during construction.
- Crowding trees with roads, walkways, and buildings.
- Planting the wrong tree in the wrong place.
- Developing a tree hazard prevention plan with arborists.
- Checking trees for health and safety at least once a year.
- Consulting arborists for advice before construction starts.
- Learning more about trees read A NEW TREE BIOLOGY.
- Making decisions based on an understanding of tree biology.
- Talking to elected officials about realistic tree support.
- Recognizing early signs of problems; consult arborists.
from 100 Tree Myths (various pages)
Old arboriculture is based on the heartrot concept where the tree is considered a passive organism and that wood is dead. Modern arboriculture is based on the concept of compartmentalization where the tree is considered an active, responding organism, and that wood does have many living cells among the dead cells.
Many trees tolerate injurious treatments. This does not mean that such treatments are good for trees.
Engineers are straight lines. Biologists are circles. More round cluster plantings of trees are needed in our straight cities!
SEE, not just look
ACT, not just wait
LISTEN, not just hear
TOUCH, not just watch
From Modern Arboriculture (p. v)
Modern arboriculture is about the tree system How it grows, how it defends itself, and how it eventually dies. I hope you will give trees and their associates - the tree system - a fair chance. Learn about them. Touch them.
These passages were excerpted with the kind permission of Dr. Shigo's daughter and co-publisher Judy Shigo Smith from
Shigo, A.L. 1986. A New Tree Biology Dictionary. Shigo, A.L. 1989. A New Tree Biology, 2nd Ed. Shigo, A.L. 1991. Modern Arboriculture. Shigo, A.L. 1993. 100 Tree Myths. Shigo, A.L. undated. New Tree Health. Shigo, A.L. undated. 5 Minute Tree Care. Shigo, A.L. undated. Shigo on Trees. Shigo, A.L. undated. Tree Hazards.
All above publications are available from the publisher
About the author
Alex L. Shigo was chief scientist with the US Forest Service, and known by many as "the father of modern arboriculture". He is recognized internationally for the development of expanded interpretations of decay based on compartmentalization and microbial succession. His research includes over 15,000 longitudinal tree dissections with a chainsaw. He has published over 15 textbooks used in many universities worldwide, and hundreds of other publications. He received numerous honors and awards. Dr. Shigo passed away October 6, 2006.
To purchase Dr. Shigo's publications or more information contact
Related editions to The Overstory
- The Overstory #181--Dispelling Misperceptions About Trees
- The Overstory #144--How trees stand up
- The Overstory #143--Dendrology
- The Overstory #132--How Trees Survive
- The Overstory #92--Trees and Their Energy Transactions
- The Overstory #70--Troubles in the Rhizosphere
- The Overstory #69--Some Tree Basics
- The Overstory #68--Twelve Tree Myths