Seed bank studies of Artemisia tridentata subsp. wyomingensis and subsp. vaseyana suggest seed dormancy in sagebrush may be subspecies-specific, but there is a lack of empirical field research verifying these conclusions. We have been investigating seed longevity of both subspecies by evaluating viability of cached seeds in the field and sampling for seeds in situ. We chose six sites in eastern Oregon, southern Idaho, northwestern Utah and eastern Nevada for each subspecies. Seeds were placed at each site during November 2006 on the soil surface in the open, on the soil surface beneath litter, and 3 cm below the soil surface. Subsets of seeds were examined twice a year, in April and November, from 2007 to 2008 to determine how the proportion of viable seeds changes over time in these differing habitats. The objective of this study was to characterize the variation in plant community composition and environmental factors of these sagebrush habitats and evaluate seed longevity within that variation. Nonparametric multidimensional scaling (NMS) with the Sørensen distance measure was used to assess plant community composition. Environmental variables and seed viability responses were overlaid onto final ordinations to evaluate relationships of seed viability and environmental factors with species composition.
Results/Conclusions
Preliminary results indicate that viable seeds in surface treatments sampled in April and November 2007 were more abundant in sites with high canopy cover and elevation. By April 2008, there were more viable surface seeds in lower elevation sites with high moss and lichen crust cover. Viable seeds under litter were greater in sites of high elevation and canopy cover in April 2007, November 2007, and April 2008. The proportion of buried seeds that remain viable is very similar across sampling times and seeds are found in equal abundances among all the sites. This study suggests that seeds of big sagebrush remain viable for longer than one growing season. Our preliminary conclusion is that the abundance of viable seeds at any given time depends on where seeds are located within the seedbank. Seeds on the surface and under litter are influenced by habitat differences while buried seeds are more or less insulated from the effects of the environment.
