Flight path of leaves is dependent on breezes

Boy, did the leaves really start falling from the trees last week. Most will continue until they are all off in a few weeks. With some trees, such as water oaks, it takes most of fall and winter for all the leaves to come down.

As most of you know, even without a single tree in your yard, you can still be blessed with massive numbers of leaves. Fallen leaves can travel for miles or disintegrate within a few feet of their tree. The more surface area and the lighter a leaf's weight, the greater its chance of blowing far away.

Leaves begin their journey as life slowly ebbs in the fall. The leaf stem contains strong, woody connections between the leaf and trunk. Wind, rain, or animals can snap off these connections. When they break, the leaves fall.

A leaf's drop from the tree is when it has the greatest chance of traveling the farthest. On dry, windy days, leaves can swirl and sail hundreds of yards.

Once on the ground, leaves can be pushed along by breezes. If they become wet or matted down, they will stay in one spot and decay. If they keep drying and become lighter, wind-buoyed flight becomes more likely.

Take a look at the leaves on the ground. Most don't lay flat. The same internal structures that held the living leaves upright on the tree now keep them from lying perfectly flat against the ground. As they dry, many leaves twist and curl.

Not only does the leaf blade help catch the wind but the stem, or petiole, also can act as one leg holding the leaf above the ground.

A leaf with several lobes and supporting veins can dry into a multilegged stool holding most of the leaf blade off the ground. The rolling and curling of a leaf can produce a "box kite" effect that the wind can catch.

Other leaves are small and light enough to remain nearly flat now but blow like snowflakes across a yard. Most leaves cup or change shapes in some way, which allows quicker drying and better sailing at slower wind speeds.

After the leaves' fall from the tree, the wind tumbles and sweeps them along. This is most noticeable on pavement and short-mowed grass. As leaves tumble, especially on hard surfaces, small pieces are broken away. These pieces can lay close to the ground and have less sail area for the wind to catch.

The closer they get to the soil surface, the greater the chance that leaves will absorb more moisture, and at the physical surface of the ground or pavement, the wind speed is zero. The closer to the ground a leaf lies, the less chance for wind to pick it up.

Leaves gather in drifts where the surface is rough enough to catch them or the air turbulence produces small patches of less wind. The size of the leaves and the height of the drift show how much wind energy is present.

Bigger leaves gather at a tall curb edge or along fences. Small leaves drift around corners and behind low landscape objects. Pine needles stay close to home once they drop because they're hard for the wind to pick up. Some curled or rolled oak leaves can go on long journeys.

Somewhere, the leaves will find a final resting spot at forest edges, house foundations, porch sides or stream beds. There, they are matted down and moistened by winter rains. Fungi and small animals chew and consume the remaining parts. The result is the recycling of the soil and air that made the leaf in the first place.

Blowing leaves are just one step ahead of recycling, so excuse me as I go blow and rake up the leaves from my yard and driveway before they blow to the neighbors' yards, especially the one that doesn't have a single tree.

SID MULLIS IS THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE IN RICHMOND COUNTY. CALL 821-2349, OR SEND E-MAIL TO SMULLIS@UGA.EDU.