There's an attraction between trees and children.

A tree's constant motion, even in still air, and its great size and reach make it fascinating. At some time in your life you've imagined, or maybe even built, a tree house.

When you see your 10-year-old headed toward your yard tree with a hammer, nails and scrap lumber, immediate decisions need to be made.

The only major concern is the child's safety. But there are some minor tree issues to think about.

Tree houses should be designed to rest on major branches and nestle around the tree trunk. Never wound the tree with nails, screws and saw notches.

Trees bend and twist in the wind. So simply jamming or wedging boards between branches or into crotches will lead to failure. Use rope to make sure a tree house stays snug against a branch.

Attaching it to branches with rope can keep windstorms from blowing it away. It can keep ambitious and ingenious children from changing design concepts and injuring themselves, too.

Carefully consider how children will enter the tree house. Don't nail ladder rungs into the trunk. Use a self-supporting ladder tied to the tree or a heavy, unlooped, knotted rope. For many trees with low branches, children don't need a ladder or rope for entry.

Next, determine how high to build it. For most play, any height represents the thrill of a tree house.

Build it for easy, safe access, not to maximize height. Always build in the bottom one-third of the tree. And position it so it rests or is attached to the basal one-third of each branch.

Use wood to build it. Wood is "soft" on the tree and children, is strong for its weight and withstands bending and mechanical shocks well. Attach the main floor pieces or braces to branches with heavy rope in multiple wraps.

Well-connected, large tree branches should support the weight of a tree house. Use rope attachments to keep it in position on branches but not to bear its full weight. Tie up all loose ends of rope, or melt them into knots.

Remember, tree houses should be temporary, seasonal structures that are removed each year. This allows a tree time to adjust and a parent time to check and repair the tree house. Use new, synthetic, heavy rope to reattach it each year.

Slightly tilt the floor to shed water. Allow any water falling on the tree house to run off away from the tree trunk. Don't allow water and leaf litter to accumulate.

Leave thin, open gaps along the bottom and top of the tree house to allow for good air circulation and plenty of light, and to let breezes blow tree litter away.

Don't install or allow wires, electrical lines, heat sources, fires or metal poles in or around a tree house. Any tree-selection process for building a tree house should have already eliminated trees near utility lines, antennas, chimneys and overhanging roofs.

A tree house structure will weaken over time. Check it monthly, remove it in the cold season, and examine it after every storm.

They may be for kids, but tree houses require adult construction and supervision for safe play and for minimizing damage to the tree.

Tree houses are inherently dangerous and require careful maintenance. But they can be fun, educational and challenging, too.

Remember to defend the life of a tree that will stand long after any tree house is gone and the children have departed. Piece together your tree house carefully to reduce major, long-term tree injuries.