In lieu of an abstract, here is a brief excerpt of the content:

  • Cold Hardiness in Wyoming Big Sagebrush Seedlings:Implications for Nursery Production and Outplanting
  • Kayla R. Herriman (bio) and Anthony S. Davis (bio)

Throughout much of the interior western United States, Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) is a keystone species, serving an important ecological role in sagebrush steppe and Great Basin sagebrush vegetation types (Lysne 2005, Lambrecht et al. 2007). Over the past century, these ecosystems have been degraded by fire, invasive species, and destructive land use including livestock-inflicted grazing pressure. Because of overgrazing and the low resilience of these ecosystems, invasive species, such as cheatgrass (Bromus tectorum), are able to establish, increasing wildfire size and frequency and promoting an unnatural fire cycle that prevents re-establishment of native vegetation (Lysne 2005, Mack 2010).

Restoration of sagebrush ecosystems has only recently been emphasized due to the loss of increasingly valued native communities, but plant establishment has focused predominantly on direct seeding. Once established, Wyoming big sagebrush maintains a relatively high rate of persistence; however, seedling establishment can be erratic, and there have been numerous failures from direct seeding (Lysne 2005). Germination and establishment can be low due to seed quality, animal foraging, water stress, and inadequate light or temperature conditions.

Planting nursery-grown sagebrush seedlings could provide a more effective method of restoring sagebrush ecosystems, especially when cost and availability of locally adapted seeds are considered. Although the initial cost of planting with seedlings is higher than that of direct seeding, largely due to costs associated with nursery production and material, this strategy may prove to be more cost effective over time. Container seedlings have greater establishment success in cold, arid site conditions, while establishment on direct-seeded field sites can be unpredictable and uneven (Romo and Young 2002).

Producing nursery grown seedlings requires some separation from natural environmental conditions. The physiological condition of seedlings at the time they leave the nursery can dramatically impact plant establishment success after outplanting. Given the larger diurnal and seasonal temperature fluctuations to which Wyoming big sagebrush plants are exposed following outplanting (Lambrecht et al. 2007), understanding tolerance to such stresses during nursery culture is of great importance. Cold hardiness refers to the capacity of a plant tissue to withstand exposure to freezing temperatures and can be induced by factors such as photoperiod reduction, decreased soil moisture, or colder temperatures. Young seedlings can be damaged or killed when exposed to temperatures that exceed their cold hardiness level (Hou and Romo 1998); therefore, planting seedlings that are sufficiently cold hardy may aid in Wyoming big sagebrush establishment.

We initiated a study to characterize the level of cold hardiness of Wyoming big sagebrush across a period of seedling production with the aim of improving overall seedling quality for restoration of degraded sites. In May 2007, we sowed 5-10 seeds (Humboldt and Elko counties, NV sources) into Styroblock™ (Beaver Plastics, Acheson, Alberta, Canada) containers at the United States Department of Agriculture Forest Service Rocky Mountain Research Station greenhouse (Moscow, ID; 46° 43.905' N, 117° 59.831' W). Once seedlings had emerged (approximately 3 wks after sowing), we thinned and transplanted them to ensure that each container was filled with a single plant. At approximately 24 wks following sowing, we moved the seedlings to the University of Idaho Franklin H. Pitkin Forest Nursery (Moscow, ID; 46° 43.388' N, 117° 57.431' W) for hardening and overwintering in an open-wall greenhouse. Throughout the growing season we applied fertilizer and irrigation as needed based on operational standards. We arranged seedling containers in a completely randomized design with each individual seedling as the measurement unit and periodically rearranged containers to ensure there was no undue influence of micro-environmental growing conditions. From September 2007-March 2008, we recorded chilling hours to assess [End Page 101] length of time exposed to critical temperatures for dormancy induction using iButton Thermachron® temperature sensors (Maxim/Dallas SemiConductors, Dallas, TX).

We determined seedling cold hardiness on 4 dates in 2007 (5 November, 19 November, 5 December, and 20 December) and once in 2008 (19 March) using freeze-induced electrolyte leakage. We collected leaf tissue samples from the top third of each of 15 randomly selected plants at each test date...

pdf