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Introduction
Trees are important to us, but they can be dangerous. Whether near a home, in a campground, or grouped together in a forest, any standing tree has In the wilderness, falling trees present no hazards; the tree failure occurs in its rightful place. It is only when in contact with human beings that dangers exist. Injury and death from trees and limbs falling on unsuspecting individuals or homes pose a very real problem. In order for humans to live in safety with their tree environment, potential hazards must be identified and corrected, or avoided. Incidents of injuries, deaths and property damage by failed trees are on the rise. As the population increases, human encounters with trees increase. When trees and forests had only occasional encounters with people and there were only a few homes in the woods, the chance that a failed tree would strike someone or their property was slim.
Today, more homes are being built in more forest remnants, and more people are visiting forests, parks, camps, and recreational sites. Trees failing, and subsequently falling, are a normal and integral part of a functioning forest. Trees break, lean, lose limbs, get sick, become infected with insects, fall, and die. In the forest these failed trees provide habitat for wildlife, nursery for vegetation, and nutrients for the soil, and a vast array of life flourishes as a result. Failed trees also allow sunlight to penetrate the forest canopy, energizing the forest floor. Contact with human beings does not alter this cycle but causes an unnatural disturbance and has a negative impact on the system. This natural event can become a destructive force when failed trees destroy homes and other structures or strike humans. Normal trees become hazardous as a result of their encounters with outside factors such as weather, insects, pathogens. In addition, soils, topography, and people influence how trees behave. The theory of hazard tree management is based on an understanding of the physiology of trees and their relationship with adversarial forces such as those listed above. Tree physiology is important because a tree’s basic structure greatly influences its balance and therefore plays an instrumental role in whether a tree fails or remains standing. If, for example, a healthy tree loses a branch in a storm, then its balance is weighted to the other side. The tree will ultimately grow new branches and foliage to recreate its balance, but for a brief time there is some instability. Tree pathology is also important because any decay in a tree weakens its structural integrity. Once a pathogen invades a tree’s structure, it will affect that tree for as long as it stands. Trees do not have any healing capability. The properties of the soil are important because it is the medium that provides the trees with life-supporting water and nutrients. Furthermore, the soil is what the tree grabs onto when threatened by storms. Weather is important because, other than humans, it is the single most challenging factor trees face. Insects attack trees. They eat the foliage, raise their young in the bark, wood, and in the tree’s cavities, and their young girdle trees from feeding. Fungi attack and can cause decay anywhere on a tree. From its roots to its leaves or needles, mechanical injury is an important factor because it exposes the tree’s fibers to fungi and decay. Topography influences a tree’s development because where a tree grows (for example, on the top of a hill versus the side) determines its weather exposure. Failed tree accidents are somewhat preventable. After a storm there is usually a lot of damage from failed trees, but prudence in a community can minimize these damages. A severe storm can knock down parts or all of even a healthy tree, and nothing can be done to prevent this. But wind or storm of any degree is much more likely to cause failure in sick or defective trees. Very weak or dead trees can even fail on perfectly calm days. Calm day failure is irresponsibility at its worst because such an event is totally avoidable.
When a tree begins to lose strength as a result of one or more adversarial relationships, it usually presents signs that a This book presents information on recognizing and interpreting those signs and how to incorporate them into a damage and injury prevention program. Correcting a hazard tree situation before an accident occurs is crucial to protecting ourselves, staff, invited guests, and the public. The Hazard Tree Handbook is vital reading for:
This second edition is updated with more comprehensive information including a glossary and lists of trees’ relative shade tolerance and expected mature heights. As people live closer to the forests and use them for recreation and aesthetics, it becomes more important for all camp managers, homeowners, and recreation enthusiasts to be informed about what makes trees less than safe. Readers will learn how to differentiate between a healthy tree and one that is defective and dangerous; to interpret which trees have the potential to cause harm and act before they do. By using the information learned, all people can enjoy trees and forests safely.
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