Search Beneath Lawns Provides Insight Into Backyard Biodiversity

When most people think of animals living in their lawns, they think of grubs and weevils devouring the roots and stems of their manicured turf, but when Loren B. Byrne, graduate student in the intercollege ecology program at Penn State, thinks about what is under the lawn, he sees much smaller organisms that are beneficial for the soil and lawn.

"Turfgrass lawns are everywhere in urban and suburban landscapes," Byrnes told attendees today (Aug. 7) at the 2003 Ecological Society of America annual meeting. "Little is known about the tiny arthropods that live in and under the grass, but these are some of the most diverse and abundant creatures on Earth. They are essential for decomposition of organic material and for nutrient cycling,"

Byrnes, working with Dr. Mary Ann Bruns, assistant professor of agronomy/soil microbial ecology, and Dr. Ke Chung Kim, professor of entomology, conducted an observational study of the arthropods living in existing lawns in State College, Pa. He sampled the bugs from low-maintenance lawns -- mowed, but with no applications of fertilizers and pesticides – and high-maintenance lawns – mowed and treated with applications of fertilizers and pesticides from a lawn care company. For comparison to the lawns, he sampled arthropods form unmowed fields in the urban landscape that were not treated with chemicals.

Byrnes identified four examples of each of the three grassy areas. He took 15 soil samples from each of the plots and extracted the arthropods using a standard method and counted them.

The preliminary investigation showed that the number of mites was highest in the high-maintenance lawn and lowest in the reference or control areas.

"This was counter to what we expected," says Byrne. "Perhaps it is because high-maintenance lawns have more grass clippings and so harbor more bacteria and fungi for the mites to eat. Or, perhaps some of the predators are reduced by the chemicals and the mites are able to increase in number."

These nanometer to 2 or 3 millimeter-sized bugs are not parasitic and are beneficial to the soil structure and the grass and other plants.

The Penn State researcher also looked at a group of arthropods called collembolans or springtails that are 2 to 3 millimeters in size and come in three varieties. The poduromorphid collembola or grub-like springtails appear unaffected by both mowing and chemical applications. These collembola live deep in the soil, where they are protected from the effects of mowing or chemicals.

The entomobryomorpha collembola were most abundant in the low maintenance lawns and reduced in the high maintenance lawns.

"These Collembola live at the soil thatch interface and so are exposed to the chemicals used on high maintenance lawns," says Byrne. "Mowing increases the thatch and therefore improves the habitat for entomobryomorphas compared to unmowed fields."

The third group of collembola is the sminthurds, also called globular springtails. They live in the thatch and on the vegetation. The highest populations of globular springtails were found in the unmown reference locations. Both chemicals and mowing reduced the number of these bugs in the high and low-maintenance lawns.

Insects like ants were most abundant in the unmown reference areas, which suggests that many insects are negatively affected by chemical applications and mowing in lawns.

"While our results are preliminary, they do indicate that a high-maintenance approach increases mite populations and that low maintenance lawns have the highest populations of some collembolans," says the Penn State scientist. "To understand the effects of lawn management on arthropod communities better, we now need to look at the species diversity of the populations, not just the numbers of individuals."