Loren Byrne scoops up a handful of dirt, sniffs it, and smiles. The organic matter that arthropods eat goes right through them, he explains. That's what gives the soil its rich black color.
James Collins
Lawns, symbol of suburbia, have rarely been studied as ecosystems.
Byrne uses his free hand to point out a quick-moving white speck called a springtail—a tiny insect named for the tail-like appendage it uses for locomotion. Springtails and mites are the arthropods most frequently found in soil, explains Byrne. And arthropods—the group whose hard-shelled members include insects, millipedes, centipedes, and crustaceans—are the most abundant animals on earth.
Byrne, an ecology graduate student at Penn State, is taking advantage of this abundance to study the health of an American archetype: the suburban lawn. Most research on lawns has focused on pest management and aesthetic conditions, but few ecologists have really studied the lawn as an ecosystem, he explains. Analyzing the arthropod population, Byrne says, is a good way to start. Because arthropods respond to environmental changes very quickly, their presence may be a good monitor of overall health.
Byrne spent the summer of 2001 comparing arthropod populations in high- and low-maintenance lawns, as well as unmowed locations. High-maintenance, he explains, is that lawn with the perfect, crisp, green grass mowed to perfection, saturated with fertilizers, herbicides, and insecticides to keep out weeds and preserve its aesthetic appeal. The low-maintenance lawn is also mowed regularly, but the lack of chemical applications has allowed plants other than grass to infiltrate and create some diversity. Finally, the unmanaged plot—Byrne's control—is that wild piece of land on the corner, too overgrown to properly be called a lawn. Here, a variety of plants run riot, blissfully ignorant of the workings of both lawn mowers and chemicals.
Byrne took 15 soil cores from each of the three types and extracted the arthropods with a homely but effective device known as a Tullgren funnel—a soda can with the top and bottom removed and a plastic funnel attached to one end.
After collecting the arthropods, he spent many hours in the lab counting and identifying them. Byrne found that his high-maintenance lawns had more soil mites than both the low maintenance lawn and the unmanaged plot, but lower populations of other arthropods. Since soil mites feast on fungi and decaying organic matter, he says, their abundance is most likely due to the plentiful presence of grass clippings, on which fungi grow. The use of fertilizer speeds grass growth, perpetuating the cycle.
The low-maintenance lawns, by contrast, had the highest number of total arthropods, due to a large number of springtails. Like the mites, springtails eat fungi and decaying organic matter. But springtails may be more sensitive to pesticides and other chemicals, Byrne speculates. Larger insects, such as ants and beetles, he adds, are affected by both chemicals and mowing, and survive best in unmowed fields.
One conclusion I draw is that lawn management practices—mowing and chemical applications—affect different groups of soil arthropods in different ways, Byrne says. Although this is a general statement, it's important, because it illustrates varying tolerance levels for human activities. Studying how organisms respond to lawn-management practices, he continues, can provide insight into a lawn's basic biology and ecology, which can then be used for the development of more sustainable, and more efficient, landscape management.
Loren Byrne is a graduate student in ecology; lbb130@psu.edu. He won third place for Health and Life Sciences at the 2002 Graduate Exhibition. His advisers are Mary Ann Bruns, Ph.D, professor of agronomy in the College of Agricultural Sciences, 415 Agricultural Sciences and Industries Bldg., University Park, PA 16802; 814-863-0779; mvb10@psu.edu; and K. C. Kim, Ph.D, professor of entomology in the College of Agricultural Sciences, 501 Agricultural Sciences and Industries Bldg., University Park, PA 16802; 814-865-1895; kck@psu.edu. His work was supported by the Luerssen Fund in the College of Agricultural Sciences and the Intercollege Graduate Program in Ecology.