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This page contains many resources to support you in the study and understanding of Arboriculture. You’ll find background information, a glossary, a list of books & publications, as well as a list of links to other arboricultural web sites. Use the links in the menu above to access the different sections, or simply scroll down this page.

Arboriculture Background
A Little About Trees in the Urban Landscape
Trees are some of the oldest and largest living things on earth providing great pleasure and many benefits to man. To understand why we need to care for trees and what kind of care they need, it is a good idea to start with understanding the difference between trees in their natural habitats and trees in the urban landscape.

Trees evolved as grove organisms existsing in cooperative groups. Trees that grow in a forest, or in a group, are under much different conditions than those which grow in an urban environment. A forest by definition is a whole ecological system where trees and other plants, animals, and organisms support each other ecologically.

When a tree grows as a solitary individual, the conditions are dramatically different. It no longer has the same support and protection of other trees and organisms, and its growth and behavior are unlike those found within a natural habitat. There is the added influence of roads, buildings and unnatural landscapes created by man.

An experienced arborist is necessary in order to ensure that the tree is safe and healthy to survive in the urban environment. Having knowledge of a tree's origin and natural habitat helps in understanding some of the problems it may have, or how to either eliminate or reduce those problems. It is essential to take note of the fact that the label “Tree Surgeon”, as used in the past, is now outdated. Indeed, scientific research by Dr. Alex Shigo and others has shown many of these obsolete practices to be harmful to the long term health of the tree.

Plant Health Care
The International Society of Arboriculture (ISA) was formed in 1924 to foster research and education worldwide for professionals in the tree care industry. Plant Health Care (PHC) was developed in the 1980s to provide a more holistic approach to maintaining the care of trees and other plants in the landscape. The focus is upon the plant rather than specific pests or disease, and the key is a broad base of knowledge. This is a field which is changing every day as more research is done in the field of arboriculture.

Based on the information that has come about in arboriculture, the ISA has developed standards for proper pruning and care of trees as well as safety guidelines. For example, in addition to being unsightly, improper cuts on trees can lead to serious future problems. To prevent this, Natural Target Pruning is employed. There are many other rules and guidelines for the proper care of trees and shrubs.

Additional Thoughts
Things have changed a great deal over the years in the tree care industry. With a little research and investigation, one can feel confident that their trees will be taken care of appropriately. Please use the links on this Web site to gain more knowledge on arboriculture. The International Society of Arboriculture web site for consumers is particularly useful.

The science and art of caring for trees and other woody plants.

Branch Bark Ridge: The point just outside the branch collar at the base of a limb is the branch bark ridge.

Branch Collar: The swollen area or “shoulder”, where the branch joins another branch or trunk of the tree. This is the “protection zone” of the branch and should not be violated.

Cloud Pruning: Pruning limbs in such a way as to create space between them and flatten the top and bottom. An example would be the work done in Japanese gardens, where one can see the appearance of “clouds.”

Crown: Refers to the canopy of the tree, which includes all the limbs from the bottommost to uppermost part of the tree.

Espalier: The training of trees or shrubs to grow flat against a wall or fence. This is best started when the plant is young but sometimes an older plant can be directed, to some degree, in this fashion if done with care. There are many styles, formal and informal of espalier.

Grooming: A term we use to describe basic pruning on a tree, also called “crown cleaning.” This includes removal of dead, diseased, damaged, and deranged, (crossing and crowded), material in the tree. We call it the “Four Ds.”

Natural Target Pruning: Aiming at making the cut just outside the branch bark ridge so that the branch collar is not violated and at the same time a stub is not left.

Pollarding - click for larger photoPollarding: The technique of pruning back yearly growth on a tree to maintain a given size and appearance. Pollarding should be started when the tree is very young, and should not be confused with topping.
Click for larger photo

Topiary: Traditionally, a very old form of pruning where trees or shrubs are shaped or ‘sculptured’ into geometric shapes, animals, birds, or other things. The shaping of a hedge to achieve and maintain certain shapes or angles to fit a particular landscape architecture could be considered to be topiary.

Topping - click for larger photoTopping: Not to be confused with pollarding. Topping is the process of cutting back limbs to a ‘stub,’ with very little or no remaining foliage left on the tree. This is very detrimental to the tree and in the long run ends up costing more money.
Click for larger photo

Windsail: Refers to the mass of the tree being affected by mechanical wind force. An overly dense canopy acts like a tightly woven sail in resisting the wind’s force.

Books and Other Publications
Tree Basics—by Dr. Alex Shigo
A basic outline of tree anatomy and physiology.
Tree Pruning—by Dr. Alex Shigo
A book that is easy to read and easy to understand, with many photos on the correct pruning of trees.

(See Dr. Alex Shigo's web site)

Stupsi Explains the Tree—by Claus Mattheck
A cartoon book that explains the structural mechanics in trees in a simplistic and simple way for the layman.

Trees - The Visual Guide—by Allen J. Coombes
A softcover field guide with more than 500 species of trees from around the world with color pictures.

Trees for Urban and Suburban Landscapes—by Edward F. Gilman
A very comprehensive guide for selecting the right tree and how to care for it. It has details on over 1,000 species of trees in North America.

Pests of Landscape Trees and Shrubs - An Integrated Pest Management Guide—University of California publication #3359.
A wealth of information to help maintain healthy landscapes.

Related Links
Links go to external web sites and will open new windows.
Some web sites may not always be available.

American Society of Consulting Arborists (ASCA)
California Oak Mortality Task Force
Center for Urban Forest Research (Report, PDF 4.8 MB)
Friends of the Urban Forest SF
International Society of Arboriculture (ISA)
San Francisco Tree Council
Student Society of Arboriculture
Tree Care Industry Association (TCIA)
Tree Education and Philosophy by Alex L. Shigo
(See Dr. Shigo's books)
Western Chapter ISA- an excellent site for more info about tree care.
Links to more Arboriculture organizations

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