Location: Great Basin Rangelands ResearchTitle: Big sagebrush seed bank densities following wildfires
Submitted to: The Progressive Rancher
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2017
Publication Date: 2/6/2017
Citation: Clements, D.D., Harmon, D.N. 2017. Big sagebrush seed bank densities following wildfires. The Progressive Rancher. 17(2):36-38.
Interpretive Summary: Opinions continue to differ on the importance of seeding big sagebrush following wildfires from “we have plenty of sagebrush” to “we have lost millions of acres of sagebrush”. Another opinion that differs is whether big sagebrush has the ability to build seed banks and return following wildfire events. This is important as big sagebrush is a common species purchased and seeded in restoration/rehabilitation efforts throughout the Intermountain West. Formerly big sagebrush/bunchgrass communities that provided critical habitats to wildlife and sustainable grazing resources have been converted to annual grass dominance. With the increase in wildfire frequency throughout the Intermountain West from cheatgrass (Bromus tectorum) fueled wildfires, many habitats have been converted to cheatgrass dominance with no sight of shrub return, especially Wyoming big sagebrush. The return of big sagebrush to a community following wildfires can be a very slow process, especially with the increase in wildfire frequencies throughout the Intermountain West, largely from cheatgrass fueled wildfires. Due to the various conversations concerning big sagebrush seed banks and its’ ability to return following wildfires we initiated a study back in 2006 to address this concern. We studied the ability of big sagebrush to build seed banks as well respond to artificial seeding by broadcasting big sagebrush seed following wildfires at two sites in northern Nevada. We found no evidence that Wyoming big sagebrush builds seed banks, but we did find that mountain big sagebrush does have the ability to build seed banks. The question though is, are resource managers willing to allow this process to take hold on their own even though it may be 20+ years for this event to unfold, or are they more apt to seed the site in an effort to speed up this process. Does this effort in fact speed up this process? Plots that we have established in other mountain big sagebrush communities often yield shrub densities 73% lower than unburned islands 15 years after the wildfire event, not significantly different than those habitats that were not seeded with big sagebrush species. The importance of wildfire suppression on rangelands is paramount to providing productive big sagebrush/bunchgrass communities for wildlife and sustainable grazing resources, especially in Wyoming big sagebrush plant communities, which just happens to make up the largest plant community in the Great Basin.
Technical Abstract: Big sagebrush (Artemisia spp.) is a critical shrub to many wildlife species including sage grouse (Centrocercus urophasianus), mule deer (Odocoileus hemionus), and pygmy rabbit (Brachylagus idahoensis). Big sagebrush is killed by wildfires and big sagebrush seed is generally short-lived and do not survive wildfires. Due to the various conversations concerning big sagebrush seed banks and its’ ability to return following wildfires, we initiated a study back in 2006 to address this concern. We selected two sites in northern Nevada that burned in the summer of 2006, one being a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and the other being dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana). We found no evidence that Wyoming big sagebrush has an active seed bank following wildfire as we recorded no seedlings in our bioassay measurements or the non-seeded field plots. We experienced very poor success in our seeded plots as only 3 out of the 54 plots recorded Wyoming big sagebrush recruitment, averaging less than one per plot. The mountain big sagebrush plots at the Sand Hills site did however, yield results that suggest that mountain big sagebrush has an active seed bank. We recorded 6.7 emerging mountain big sagebrush seedlings/10 ft² in the 30’ plot and 1.8 emerging seedlings in the 3’ and 100’ plots on the south edge of the burn which is the northern edge of the unburned habitat. The north edge recorded an active seed bank at the 3’ plots, at 1.8/plot. Seven of the 54 seeded plots recorded recruitment of big sagebrush which average 1.3/plot. Wyoming big sagebrush sites are more xeric and have less site potential. The difficulty in restoring or revegetating these xeric sites following wildfires is well documented. Once these sites burn, if there is not an active and successful weed control and restoration/revegetation plan implemented these sites are often converted to cheatgrass dominance. Wyoming big sagebrush sites tend to dry out earlier in the season, therefore increasing the risk of wildfires. Mountain big sagebrush communities on the other hand have much more site potential and therefore experience a greater potential to re-establish on their own. Mountain big sagebrush communities also stay green longer into the summer months and decrease the risk of wildfire during this green period.