A lot of trees have been damaged by snow and ice this winter. Branches have been broken off, some of which are still dangling in tree tops.

Hangers and broken branches should be removed as soon as practical, and the woundss treated. Healthy growing wood needs an active flow of sap from roots to leaves and from leaves to roots.

The sap flows up and down through long lines of cells. When these lines are broken or destroyed, they must receive proper care quickly if the tree is to make a speedy recovery. This action will also elimate unsightly stubs and the possibility of decay in and around the wounds.

It is no job for someone who is inexperienced. Big trees can be dangerous. Beware of the brittleness of frozen wood.

Large limbs are heavy and if a severed limb gets out of hand it can do a lot of damage. A misstep while climbing in a tall tree, momentary loss of balance, or misplaved confidence in the strength of a branch can cause a pruner to fall and perhaps be badly hurt.

For safety, engage professional tree surgeons to do work that requires removal of large limbs or climbing in tall trees.

Some treatment of tree wounds can be done by homeowners and the U.S. Forest Service has recently issued recommendations on how to do it in order to prevent decay.

"Decay is a major cause of damage to trees," Forest Service specialists said. "Wounds start the processes that can lead to decay. Decayed trees are unsightly, hazardous, and low quality.

"To prevent decay, first prevent wounded, follow these steps to minimize decay, and to help the tree remain halthy:

"Clean wounds; trim away loose injured bark.

"Shape the wound into a vertical oval when possible. Use a sharp knife to make a clean hedge between vigorous bark and exposed wood.

"Remove dead, dying or weak branches from the wounded tree.

"Water and properly fertilize the tree.

"Remove dead wood from around tree - practice sanitation.

"Remove less valuable woody plants that may be crowding te valuble wounded tree.

"Protect the tree from further injury.

"Use a thin coat of wound dressing only if it's needed as a sign that the wound has been treated. Otherwise do not paint the wound."

Dr. Alex L. Shigo, chief plant pathologist, Forest Service Sciences Laboratory, Durham, N.H., has done a lot of research on the decay of trees, and he questions the value of painting tree wounds. In tests he found the wound dressing did not prevent the invasion of microorganisms.

"The chemical changes that occur following wounding are most important. This is the first line of defense by the tree.

"Why is it some trees can stop the processes that result in decay and others cannot? We need to determine what goes on immediately after wounding and learn why some trees have a stronger wound response.

"Then if you can help the tree to produce more of the chemicals necessary to stop infection, we will have done something."