Background/Question/Methods
Seed bank studies of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) conclude that seed banks are transient, with little seed carry-over. Germination studies of mountain big sagebrush (Artemisia tridentata ssp. vaseyana) in a laboratory setting have shown evidence of seed dormancy. These studies suggest seed dormancy in sagebrush may be subspecies-specific, but there is a lack of empirical field research verifying these conclusions. Our objective was to investigate seed longevity of both subspecies by evaluating viability of seeds in the field and sampling for seeds in situ. We chose six study sites in eastern Oregon, southern Idaho, northwestern Utah and eastern Nevada for each subspecies. Ninety-six polyester mesh bags, containing 100 seeds each, were placed at each site during November 2006. Seeds were placed on the soil surface in the open, on the soil surface beneath litter, and 3 cm below the soil surface to determine whether dormancy is affected by continued darkness or environmental conditions. Subsets of seeds were examined in late April and November 2007 to determine how viability changes over time. Initial viability of seeds was 81% (vaseyana) and 92% (wyomingensis).
Results/Conclusions
Data were analyzed using PROC GLIMMIX (SAS Institute) and are presented with 95% confidence intervals. Preliminary results indicate the following. After remaining in the field for one year, buried Wyoming big sagebrush seeds retained 12-45% viability, while seeds under the litter and on the surface were 2-13% and 0-4% viable, respectively. Buried seeds of mountain big sagebrush were 5-51% viable. Seeds under the litter and on the surface retained 1-15% and 0-7% viability, respectively. Big sagebrush seeds can stay viable for more than one growing season and support observations of seedling emergence where sagebrush seed was thought to be absent (e.g., in the interior of large burns or years after reseeding efforts). However, we have yet to understand the significance of the “seed bank” to the overall population. Sagebrush communities are threatened by conversion to exotic annual grasslands, agriculture and urbanization. A more thorough understanding of seed longevity and dormancy will aid land managers in making informed decisions regarding restoration and conservation of these communities.