1. Establishment of Milkweed Seeds under Different Conditions
Marvin E. Sibrian and Timothy L. Dickson
Department of Biology, University of Nebraska at Omaha, 6001 Dodge Street, Omaha, NE 68182
Introduction
Milkweed is an important food source for many insects, and the only food source
for monarch caterpillars. Unfortunately, the abundance of milkweed plants has
been decreasing over the years due to Roundup Ready® crops and increased
herbicide use in agriculture (Hartzler 2010), as well as milkweed habitat being plowed
under for increased corn acreage. In February 2015, the U.S. Fish and
Wildlife Service (Fears 2015) calculated that since 1990, the annual migration of monarchs has decreased by about one billion individuals.
In hopes of restoring the monarch population, conservation organizations are joining
forces to grow as much milkweed as they can and to increase the number of milkweed
individuals by one billion (Marcotty 2015). However, it is unclear how many seeds must
be sown to add one billion milkweed individuals because there is little information
regarding the establishment rates of milkweed from seed. I proposed to add milkweed
seeds under different growing conditions to quantify the survival and establishment of
milkweed seeds.
Figure 1. Annual area of monarch butterflies overwintering in Mexico from (the number of monarchs is estimated from the area of trees covered by monarchs, Fallon et al. 2015).
Results
Methods
The experiment was conducted at UNO’s Glacier Creek Preserve. To determine the optimal growing condition for milkweed, the responses of three different species of milkweed seeds (Asclepias syriaca, A. tuberosa, and A. viridis) growing under three different treatments were examined (each treatment replicated six times). The three treatments were: (1) 100 seeds of each milkweed species sown in April 2016 into plots with bare soil, (2) 100 seeds of each milkweed species along with a mix of four prairie grasses and five forbs sown into plots of bare soil, (3) 100 seeds of each milkweed species sown into plots of already intact vegetation. The bare soil treatments were on land that has been farmed for corn and soybeans for decades prior to being used in this study in 2016 (top picture on left).
I checked the plots for germination and growth three different times during the 2016 growing season. I only identified milkweed seedlings to species during the final sample. No A. viridis individuals were found. With the help of Dr. Dickson, a repeated-measures ANOVA (Fig. 2) and t-tests (Fig. 3) were used to analyze data.
Figure 2. Although milkweed survival is significantly higher in bare ground (BG) than restored prairie, there is no significant difference between the other treatments (error bars are +/- 1 SE).
Figure 3. Asclepias syriaca has significantly higher survival in the bare ground (BG) treatment where only milkweed is seeded compared to where milkweed and other prairie seeds are seeded together (error bars are +/- 1 SE).
Conclusion
Acknowledgements
Milkweed seedlings have relatively high survival in the 1st year in the absence of competition with other prairie seedlings
or adult plants.
Thanks to Dr. Dickson, the University of Nebraska at Omaha, Glacier Creek Preserve, and a UNO FUSE grant for providing the funding and opportunity to pursue this study.
Works cited:
Fallon, C., B. Borders, E. Lee-Mäder, and S. H. Black Milkweeds and Monarchs in the Western U.S.
Fears, D. 2015, February 9. The Monarch Massacre: Nearly a Billion Butterflies Have Vanished. The Washington Post.
Hartzler, R. G Reduction in common milkweed (Asclepias syriaca) occurrence in Iowa cropland from 1999 to Crop Protection 29:1542–1544.
Marcotty, J. 2015, June 6. Calling all milkweed: Federal pollinator plan needs a billion plants for monarch butterflies. Minnesota Star Tribune.