PARENT SESSION
Poster Session 37: Forest Ecology.
Thursday, August 5 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Effects of overstory density on seed banks in pinyon-juniper woodlands.
Allen, Elizabeth*,1, Nowak, Robert2, 1 University of Nevada-Reno, Reno, NV2 University of Nevada-Reno, Reno, NV
ABSTRACT- In the Great Basin, pinyon-juniper trees have expanded their range into the neighboring sagebrush steppe communities that occur at lower elevations. As trees establish and dominate, the former understory vegetation of sagebrush, forbs and grasses become sparser. These changes in vegetation dynamics are assumed to affect the seed bank by making it more depauperate as tree density increases. The aim of this project is to see if there is a relationship between vegetation and seed bank abundance and diversity. This study was conducted on a central Nevada mountain range using three plots each of high, medium and low pinyon-juniper density. We took soil samples in the fall of 2002 and germinated the seeds in the soil in a greenhouse in early February of 2003. The same procedure was followed in the fall of 2003 and the seed bank is currently being determined. In addition to aging the trees at each plot, we estimated percent coverage by species for both the understory and overstory vegetation in the summer of 2003. As expected, when the overstory vegetation increased, the understory coverage decreased (r = -0.93) and species diversity in the vegetation decreased (r = 0.83). In the seed bank, seedling density (seedling/m2) was 310, 291 and 222 at the high, medium and low densities respectively. The most common species to emerge at all plots were annual forbs, Gayophytum diffusum and Collinsia parviflora, and the perennial bunchgrass, Poa secunda. The data reveal two surprising findings. First, there was not a high correlation between seed bank diversity and abundance with either overstory or understory coverage as was expected. Though not yet examined, the contradictory results may be due to the prevalence of tree litter at high density plots, which trap seeds. Second, the density of seedlings in the seed bank was very low as compared to other seed bank studies. This may be due in part to low levels of understory coverage and low rainfall in the last three years. It is hoped that through the addition of another year of data and in depth ordination studies, patterns between the seed bank and vegetation will be elucidated.
Key words: pinyon-juniper woodlands, seed bank