DOT Project Number:  90-00-LRTF-012, 102

Fiscal Year:  2000-2001

Award:  $7,560.00

Principal Investigator:  Dr. Laura Jackson, Department of Biology, University of Northern Iowa; Dave Williams, Department of Biology, University of Northern Iowa, dave.williams@uni.edu

Summary Report:

EMERGENCE AND MORTALITY OF NATIVE PRAIRIE FORBS SEEDED INTO AN ESTABLISHED STAND OF GRASSES

Today thousands of hectares of warm-season grass plantings exist in Iowa. Many of these plantings have few to no native forbs. The goal of this project was to determine if the addition of seed and mowing could increase species diversity of a 25 year-old warm-season grass planting. I hypothesized that frequent mowing in the first one or two years after broadcasting forb seed into an established stand of warm-season grasses can increase forb emergence and reduce forb mortality. I further hypothesized that mowing would accelerate forb growth and maturation.

To test my hypothesis, I seeded 23 forb species at a rate of 3.7 kg/ha or 350 viable seeds/m2 into a 25 year-old native prairie grass seeding. I assessed and compared forb emergence, mortality, growth and maturation, over two growing seasons. I tested three mowing treatments: mow-1 (weekly mowing year one from May to September and the cutting height increased from 2" to 5" during that time period), mow-2 (bi-monthly mowing year two from May to September and the cutting height increased from 5" to 12" during that time period), and no-mow (as a control). The plots were fall burned and fall sowed by hand broadcasting. No attempt was made to incorporate seed into the soil.

I found that mowing had significant effects on forb emergence, mortality, growth and maturation. In the first growing season, mowing increased forb emergence and reduced forb mortality over un-mowed controls. Frequent mowing increased light to the forb seedlings as well as reduced vigor of the established grasses creating gaps underground for forbs to occupy. However, mowing two consecutive years did not further increase forb emergence and reduce mortality. Plant size and maturity increased as a result of frequent mowing. By year two, forbs in mowed plots averaged 223% taller shoots, 45% deeper roots and had 46 times more flowering plants than in no-mow plots.

This has implications for Iowa's 242,820 hectares of rights-of-ways. With seed as the only incremental cost, this research suggests that the a single year of managed mowing could transform species-poor native grass plantings into diverse plant communities.

Note:

Continuing work on this "forb enhancement" study resulted in an article published in the March 2007 issue of Restoration Ecology. The full article appears here courtesy Blackwell Publishing.