"Heavy grazing also increases the amount of nitrogen in the leaf material, which increases the quality of material that falls to the ground," Frank says. "The high-quality litter is quickly broken down by soil bacteria, which in turn enriches the soil around grazed plants."
Scientists have found that intensive grazing also alters important interactions between roots and closely associated bacteria. While a working in a post-doctoral position in the Frank lab, Bill Hamiltonnow an associate professor at Washington and Lee Universityshowed that grazing Yellowstone grasses stimulated the rate at which simple organic compounds are exuded from the tips of plant roots.
"These simple compounds, which are made of sugars and amino acids, are like cotton candy for soil microbes," says Frank. "The microbes thrive on the compounds."
In a series of cascading events, microbes use the food energy from the compounds to decompose organic material in the soil around the roots, which then results in a new source of nutrients for plants.
Next spring, Frank will travel to Yellowstone to fence areas of grassland that will become test plots for the study. Each fenced-in area will be about a 15-yard square and will be left untouched for a year. Over the following two years, some areas will be clipped at various intensities to mimic natural grazing. Plant data obtained from the fenced areas will be compared with adjacent areas as well as with areas of the park where natural grazing varies in intensity depending on the time of the year.
"The study will be very similar to the one we did 20 years ago on elk grazing," Frank says. "It will be interesting to see if we reconfirm our original findings or whether we find something new. We also intend to use this opportunity to better understand the complex and fascinating ways in which the interactions among plants, herbivores and soil organisms foster the stability of grassland systems."
|Contact: Sara Miller|