Research Projects

Grassland, Shrubland and Desert Ecosystem Research Program - Boise
 

Forb Research                                     

Germination ecology of Great Basin Penstemon species
Adequate seed supplies of locally adapted populations of native species are required for revegetation of degraded sagebrush steppe communities of the Great Basin. Although native forbs are essential elements of these communities, seed availability of most forb species is limited or nonexistent. We are examining intraspecific variability and developing seed production practices and seeding technology for three penstemons of the northern Great Basin. Sand penstemon (Penstemon acuminatus), hotrock penstemon (P. deustus), and sagebrush penstemon (P. speciosus) occupy different habitats and may be valuable for use in postfire seedings, mixed plantings, roadway revegetation, and low water use landscaping. Preliminary work indicated that newly harvested seed of all three species is dormant, exhibiting less than 15% germination under favorable conditions. Germination was improved by moist prechilling for 8 to 12 weeks. The prechilling requirement for sagebrush penstemon, but not hotrock penstemon, was reduced by a liquid smoke treatment. Treatments permitting more rapid and uniform germination are desirable for production of nursery stock and establishment of seed production fields for seed increase or commercial seed production.

Cultural practices for Lomatium grayi, L. dissectum, and L. triternatum seed production
Seed supplies of Lomatium species are currently not available for use on Great Basin rangelands. Production of seed fields will require development of appropriate cultural practices including seeding techniques, irrigation requirements, and control of weeds, diseases, and seed predators.

FUELS RESEARCH

Changing Fire Regimes, Increased Fuel Loads, and Invasive Species:  Effects on Sagebrush Steppe and Pinyon Juniper Ecosystems
We propose to conduct an integrated research program that addresses each of these information needs.  The first component will evaluate the spatial and temporal dynamics of the shrublands and woodlands prior to settlement by using a combination of plant community, stand structure and dendrochronology data.  It also exam8nes the influence of varying environmental conditions and invasive species on current shrubland and woodland dynamics.  the second component is closely aligned with the first.  It evaluates the changes that have occurred in fuel loads since settlement and provides a comparison of the fuel loading characteristic for ecosystems that are functional, at risk, or that have been converted to annual grasses or secondary weeds, or revegetated.  The third component uses mechanistic studies to examine key factors influencing community susceptibility to invasion by cheatgrass and the secondary weeds, squarrose knapweed and rush skeletonweed.  It examines temporal differences in resources availability among vegetation types and states.  It also evaluates the effects of plant abundance of existing species and fire on soil resource availability and cheatgrass establishment and reproduction, and the effects of fire on secondary weed establishment and spread.  This research will provide both regional and local information on characteristics of woodlands and shrublands at greatest risk of catastrophic fire, most susceptible to cheatgrass invasion, as well as most suitable for prescribed fire.  It will also provide information on the effects of resource availability, community condition, and fire on community susceptibility to cheatgrass and secondary weed invasion.

Impacts of exotic weeds on fuel loading and fire regimes in shrub steppe communities and development of technology and plant resources for their restoration
The cycle of wildfires and annual weed invasion has altered millions of acres of western shrublands and grasslands, disrupted ecosystem functioning, increased wildfire size and frequency, reduced plant and animal diversity, and set the stage for invasion by secondary perennial weeds that are even more difficult to control. Our poor understanding of the susceptibility of functional and at risk native systems to weed invasions and the impacts of weeds on fire regimes and seasonal fuel loading limits our ability to manage these systems. Criteria are needed to determine when post-fire seeding to restore native vegetation is appropriate. Reestablishing native communities necessitates the use of effective methods for controlling competitive weeds and the availability of reliable seed supplies and seed transfer guidelines for a larger suite of revegetation species, particularly native forbs.

INVASIVE SPECIES RESEARCH

EMERGENCE AND GROWTH OF WINTERFAT IN RESPONSE TO CHEATGRASS (BROMUS TECTORUM) DENSITY
Winterfat (Krascheninnikovia lanata [Pursh] A. D. J. Meeuse & Smit; synonym: Ceratoides lanata [Pursh] J. T. Howell) is a desired shrub species and an integral component of salt desert shrublands in the Intermountain West. On the Snake River Birds of Prey National Conservation Area (BOP) in southwestern Idaho, extensive loss of winterfat-dominated communities has been linked to altered fire regimes associated with cheatgrass (Bromus tectorum L.) invasions. Post-fire revegetation efforts are often hampered by the quick emergence of cheatgrass seedlings with autumn or spring moisture. We compare the establishment of four winterfat populations (Birds of Prey; northeastern New Mexico; Northern Cold Desert Select Germplasm, and Open Range Tested Germplasm) with and without cheatgrass competition. Seed of each accession was planted in 15 cm diameter pots containing four densities of cheatgrass (0, 2, 4, and 8 plants per pot) in a greenhouse. Plant measurements were made 4, 5, 7, 9, 11, 13, 15, 17, 19, and 21 weeks after planting. Measurements included winterfat survival, height and two canopy diameters and cheatgrass height and number of leaves and culms per plant. Initial establishment was greatest for the New Mexico winterfat source at all cheatgrass levels. Growth of this source exceeded the others in the absence of cheatgrass. However, the presence of cheatgrass depressed growth of all sources by at least 90 percent. Establishment of winterfat on cheatgrass infested rangelands necessitates seeding on sites where cheatgrass densities are low or reduced by site preparation procedures.

SOIL CARBON MANIPULATION FOR CONTROL OF ANNUAL WEEDS
Annual weeds that proliferate following wildfires dominate millions of hectares of rangeland in the western United States.  Revegetation with native perennial plants is not feasible in these areas without some form of weed control. Carbon application in the form of sucrose has been shown to suppress annual weeds by temporary immobilization of nitrogen in the soil profile.  Our objective was to assess the efficacy of sucrose for annual weed suppression under a wide range of treatment applications in multiple years.  The study was conducted on an area in the Snake River Birds of Prey National Conservation Area that burned in 1997.  Sucrose was applied in either early December or in both December and February at 0, 200, 400, 600, 800, 1000, 1200, 1600, or 2000 total kg-C ha-1.  In the first 2 years of this 3-year study, the maximum carbon treatment resulted in a >75% reduction in biomass production of the 2 main weed species, cheatgrass (Bromus tectorum) and tumble mustard (Sisymbrium altissimum).  For the same total amount of sucrose, a single application in December was more effective than the December/February application.  Application rates necessary for adequate weed control are probably not economical for broad-scale application after wildfire.  Use of sucrose as a carbon source may still be feasible for some high-intensity, small-area applications and in areas where herbicide use is not acceptable.

Rush Skeletonweed Research

assessment of shrub steppe communities invaded by rush skeletonweed (chondrilla Juncea L.)
Rush skeletonweed, an herbaceous Eurasian composite, was first reported in southern Idaho about 1963. From the original site near Banks and the South Fork of the Payette River, it appeared to radiate rapidly, particularly to the south and east. It is now widespread across southwestern Idaho and often produces dense stands of wiry, latex-filled plants that compete with native plant species for water and nutrients. Initial colonization sites were forest openings and higher elevation grasslands and shrublands, and local managers doubted that invasions would occur widely on lower elevation sites of the Snake River Plain. But isolated stands of rush skeletonweed are now found on the western half of the Plain in shrub steppe communities, abandoned croplands, and disturbed sites. We are assessing biotic and abiotic parameters of representative rush skeletonweed stands in a variety of communities, including those dominated by big sagebrush (Artemisia tridentata Nutt.), antelope bitterbrush (Purshia tridentata (Pursh) DC.), crested wheatgrass (Agropyron cristatum (L.) Gaertn.), cheatgrass (Bromus tectorum L.), and medusahead (Taeniatherum caput-medusae (L.) Nevski). To aid in predicting which communities and sites may be especially vulnerable to rush skeletonweed invasion, we plan to combine this assessment with a region-wide GIS analysis.

Rush skeletonweed demography following wildfire on Idaho’s Snake River Plain
Rush skeletonweed is a perennial herb native to Eurasia and northern Africa, and is classified as a Noxious Weed in the western United States and Canada. Some reports from our region note possible increases of rush skeletonweed after fire; others state that the invader will not persist on very dry sites. On the arid Snake River Plain of southwestern Idaho, we are examining rush skeletonweed population demography and life history following wildfires that burned in summer 2003.

Seed and seedling ecology of rush skeletonweed following wildfire on Idaho’s Snake River Plain
Rush skeletonweed produces prolific wind-borne achenes which mature in summer and fall and are reported to emerge with fall moisture. These seeds are often targeted for control, but their actual recruitment role compared to root sprouts has not been quantified in North America. We are assessing this role on 11 burned/unburned plot pairs in rush skeletonweed stands on Idaho’s Snake River Plain. Our efforts include excavating rosettes to determine their source from seeds or root buds, measuring the soil seed bank, assessing seed bank losses to soil microbes, quantifying seed germination in field-buried bags, and documenting emergents from field-sown seeds.

Rush skeletonweed seed germination responses
We examined germination responses of rush skeletonweed seeds that had been hand-collected from three sites on the Snake River Plain near Boise, Idaho. In each laboratory trial, replicates of 50 seeds were tested on saturated blotters in plastic germination boxes and incubated in germination chambers at constant temperature with light/dark for 12/12 hr. In tests from 6 to 34°C, germination averaged >50% of all seeds at each temperature. The shortest time to 50% germination of viable seeds occurred at 22ºC. Based on tetrazolium tests, no seeds were dormant at any temperature. Germinability by harvest date was <5% of all seeds for mid-Jul 03 harvest, increasing gradually to 78% in mid-Sep 03, then declining. Total germination varied for each of the three harvest sites: 42, 50 and 74%.