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Rehabilitation of downy brome–infested shrublands is challenging once this invasive grass dominates native communities. The effectiveness of imazapic herbicide in reducing downy brome cover has been variable, and there is uncertainty about the impacts of imazapic on native species. We used a before-after-control-impact (BACI) field experiment and greenhouse studies to (1) determine if imazapic herbicide applied at 132 g ai ha−1 (8 oz/ac−1) and seeding with two native shrub species (Wyoming big sagebrush [Artemisia tridentata] and Mexican cliffrose [Purshia mexicana]) reduced downy brome cover and promoted shrub establishment, (2) assess potential effects of imazapic on nontarget plant species and plant community composition, and (3) determine if imazapic affected downy brome or seeded shrub species when applied at different developmental stages. Seeding shrubs, alone, or in combination with imazapic application, did not significantly increase shrub density, possibly because of droughty conditions. In the field, imazapic reduced downy brome cover by 20% and nontarget forb cover by 25% and altered plant community composition the first year after treatment. Imazapic was lethal to downy brome at all growth stages in the greenhouse and reduced shrub germination by 50 to 80%, but older shrub seedlings were more tolerant of the herbicide. We conclude that a one-time application of imazapic combined with seeding shrubs was only slightly effective in rehabilitating areas with high downy brome and thatch cover and resulted in short-term impacts to nontarget species. These results highlight the need to treat downy brome infestations before they become too large. Also, removing thatch prior to treating with imazapic, although likely lethal to the native shrubs we studied, could increase the effectiveness of imazapic.

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Establishment of native grasses is a primary objective of restoration in Pinus ponderosa var. scopulorum (P. & C. Lawson) forests in the southwestern United States. Interactions among native grasses and soil microorganisms generate feedbacks that influence the achievement of this objective. We examined soil chemical properties and communities of plants and soil microorganisms in clear-cuts and P. ponderosa stands thinned and maintained at low and medium tree densities for over 40 years along with high density (unthinned) stands. Phospholipid fatty acids (PLFA) in soils were analyzed to examine arbuscular mycorrhizal (AM) fungi and microbial communities in the three thinning treatments and the unthinned stands with and without a recent broadcast burn. Additionally, two native bunchgrasses, Festuca arizonica and Muhlenbergia wrightii were grown in containers filled with intact soil cores collected from each field plot to more thoroughly compare the abundance of AM fungi and microbial communities across different stand densities and burn treatments. Tree thinning decreased litter cover and increased the abundance and diversity and altered community composition of both herbaceous vegetation and AM fungi. In the mineral soil layer, the pH, total carbon, nitrogen, phosphorus and PLFA profiles did not differ significantly among the four stand density or burn treatments. Mycorrhizal colonization of the container grown grasses did not significantly differ with tree density or burn treatments; however, F. arizonica roots had a strong trend for decreased colonization when grown in soil from high density (unthinned) tree cover. Soil from the containers with F. arizonica had a greater abundance of AM fungal spores. Furthermore, bacterial community composition varied with grass species. Concentration of biomarkers for bacteria were higher in soil that supported F. arizonica compared to soil in which M. wrightii was grown. Our results indicate that the creation of clear-cut openings in forests may increase the abundance and richness of AM fungal propagules and soil bacterial communities were surprisingly resilient to tree thinning and low-intensity fire treatments. These results suggest managing forests to create clear-cut openings generate conditions that favor understory native grasses and AM fungi that are linked to soil bacterial communities. 2015 Published by Elsevier B.V.

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In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign Language, etc.) should contact the responsible Agency or USDA's TARGET Center at (202) 720-2600 (voice and TTY) or contact USDA through the Federal Relay Service at (800) 877-8339. Additionally, program information may be made available in languages other than English.To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at http://www.ascr.usda.gov/complaint_filing_cust.html and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992.