Teri Lyn Peisner, age 7, of bus, Mich.., for his question:
What causes a hollow tree?
An old hollow tree is an apartment house for nature's children. It provides cozy homes for bats and birds, for skunks and squirrels, for bees and beetles and for armies of busy bacteria. All these small tenants helped to dig out the hollow in the ancient tree.
The proper number of limbs for a human being is four, two arms and two legs. The limbs of a tree are its branches, and it may have five or 10 or maybe more. It may live for centuries, and its limbs and trunk never stop growing bigger. Every year it adds a narrow new layer of wood around its trunk and each of its twigs and branches. The ring of new wood is created under the bark around the ring of wood that was created last year.
The trunk must do two jobs for the tree. It must be stiff enough to stand up straight and hold aloft the spreading branches. It must carry water and sweet sap from the roots and the tallest twigs. But the liquid food and water are carried only in the newest layers of wood near the outside of the trunk. If the trunk is sturdy enough to withstand gales and if new layers of wood are added every year, the tree still may be thriving for your great grandchildren to admire.
The wood in the middle of the trunk was made when the tree was a slender saplijag. It does trot carry liquid food, and when the stiff trunk is wide enough the middle section is not needed to hold up the tree. The useless old heartwood in the center of the trunk dries out. And the woods are teeming with tiny creatures searching for places to dig and forage for food. The dry heartwood is invaded by armies of busy bacteria. These distant cousins of the germs that sometimes make us sick are too small for our eyes to bee. They devour the dry old wood and break it up into decaying crumbs and rotting powder.
Hosts of insects arrive and make themselves at home. They riddle the dry old wood with tunnels and make it weaker. They lay eggs that hatch into greedy grubs, and the crumbling wood begins to fall down the center of the trunk in powdery piles of sawdust. Mosses and mildews soak up nourishment from the moist spots as more of the old wood decays to crumbs. Year by year the hollow hole grows bigger as more tenants cone to live in the old tree trunk. But the tree is not harmed. Year by year, as the heartwood crumbles away, new wood is added around the outside of the sturdy trunk.
As the hollow becomes wider and higher, larger tenants move into the sheltering apartment house. The upside down bat finds a ledge where she can sleep safely until dusk. Nearby a squirrel scrapes out a pocket in the dusty crumbs. The hollow grows bigger. A woodpecker digs a deep hole to lay her eggs, and a chickadee enlarges a small pocket and lines her nest with feathers and soft grass. High in the busy apartment house a screech owl makes himself a bed in a cozy cavity and sleeps through the day. Chances are the old hollow tree will be there to provide homes for the children and the great great great grandchildren of these tenants.