Natural Cycles

Every nine-year-old girl’s nightmare will emerge from a 17-year sleep next spring when the Periodical Cicadas (also known as 17-year locusts) come to town. Actually, the cicadas are already here, dormant in the ground, preparing to hatch in 2007.

I was nine when the grandparents of this current brood emerged in 1973. Large bugs with beady red eyes suddenly appeared, and seemed to be everywhere. Not to sound politically-incorrect, but boys loved sticking the creatures in girls’ faces, making us scream. Cicada carcasses hang around for months, meaning that the boys in my fifth grade class were still finding the empty shells when we went back to school in the fall.

News of the cicadas impending arrival got me thinking about cycles in nature. How many other natural events occur on a cycle that repeats on either an irregular schedule, or over a period of time that spans several years?

The seasons are an obvious cycle. They are predictable – spring, summer, fall, winter. Weather is less predictable from day to day, but it still has a regular pattern. In this area we average 34 inches of precipitation during the year, and expect more than half that amount to fall from May through September.

Every school-age child has heard of the “water cycle.” This cycle has repeated itself for millennia: water evaporates from rivers, lakes and oceans, forms clouds in the atmosphere, and falls onto the ground in the form of rain or snow. This is a “closed loop” cycle, where the cycling element (water) moves through the system (the earth), but does not leave the system – nor does new water enter the system. We are using water molecules today that were on the earth during the age of dinosaurs.

But what about natural cycles that are unpredictable? We have a good example in our community today. Area residents may have noticed that in some years oak trees produce a lot of acorns, but this year there are hardly any to be found. Acorns, hickory nuts, walnuts, and other large seeds are known as “mast,” and the trees that produce these large seeds are known as “mast trees.”

Mast trees are considered by many ecologists to be the “keystone” trees of a healthy woodland because of the large amount of food they generate when they produce their seeds. Wildlife rely upon the food these trees supply.

“Masting cycles” are unpredictable. Some hypothesize that the low mast years are part of a tree’s self-defense mechanism – insects that attack the seed of certain trees may die back during low mast years. Others suspect that drought conditions may influence high and low mast years.

Generally, if one species of tree is having a low mast year, other species will have normal seed production. However, once in a while, the irregular cycles of the various mast tree species coincide, and there is a scarcity of food for wildlife. This year, there have been very few acorns from any species of oak. And, while walnuts appear to have produced a normal “crop” of nuts, hickories seem to have produced fewer nuts this year than in recent years.

In addition to wildlife having less to eat this winter, another impact of low mast years is that there are fewer tree seedlings the next spring. And this brings us full-circle to our cicadas.

I spoke to Nancy Gonsiorek, chairman of the Wildflower Preservation and Propagation Committee who is also a University of Illinois Master Gardener, and she offered the following advice:

She recommends not planting trees smaller than 2 1/2 inches in diameter this fall or next spring. “Female cicadas slice several inch-long crevices in twigs and branches1/4 to 1 1/2 inches in diameter to lay eggs.  If this is done in a small tree, the trunk will snap off in the next high wind at the site where the eggs were laid.” She suggests covering small trees with pest netting (1/4 inch holes work well) to keep the cicadas from damaging the trees.

2007 could be a tough spring for young girls and young trees.