Cicadas Worth Singing About
A study shows thereÕs no need to brood about Brood X.
Cicadas may be the bane of the eastern United States every 17 years, but they do have an ecological purpose.
In addition to feeding hordes of hungry animals once every 17 years, Brood X is now known to be a nutrient source for the forest.
It was always thought that the cicada invasion was largely destructive to the forest due to the large amounts of vegetation the adults consume before mating and laying their eggs inside trees. The larvae then burrow into the ground for 17 years before they emerge as adults. Once they mate, adult cicadas die, littering the forest floor with their bodies.
Scientists had previously noted that in the years following the cicada emergence, forest plants seem to have unusually high levels of nitrogen in their leaves. Normally, nitrogen is the limiting factor in plant growth.
Louie Yang at the University of California, Davis, decided to conduct some further experiments to determine if the cicadas were actually causing the nitrogen increase.
Yang measured the levels of nutrients in soil plots both with and with out dead cicadas. He found that a month after adding the cicada carcasses, the numbers of bacteria and fungi that feed on biological material had increased. Also, the amount of ammonium and nitrate available to the plants for use had increased by up to three times.
Yang added 140 cicadas per square meter to a plot of land that contained the forest plant called the American bellflower. These plants had 12% more nitrogen in their leaves and their seeds were 9% larger than the bellflowers grown in plots without cicada carcasses.
These results showed a direct link between the cicadas and increased levels of nitrogen in plants, indicating that the cicada swarms could kick-start forest growth every 17 years and have a beneficial effect on the ecosystem as a whole.
The idea of a Òresource pulseÓ is not unusual, as there is dramatic plant growth after El Ni–o rainfalls and there is a nutrient boost to riverbank communities when salmon die after spawning.
Courtney Luke
