Ann L. Hild

Potential selection in native grass populations by exotic invasion.

Ecological impacts of invasive plant species are well documented, but the genetic response of native species to invasive dominance has been often overlooked. Invasive plants can drastically alter site conditions where they reach dominance, potentially exerting novel selective pressures on persistent native plant populations. Do native plant populations in old exotic invasions show evidence of selection when compared to conspecific populations in adjacent, noninvaded areas? We employ amplified fragment length polymorphism (AFLP) analysis to screen a large number of loci from two native grass species (Hesperostipa comata (Trin. & Rupr.) Barkworth and Sporobolus airoides Torr.) that occur in old infestations of the invasive forb Acroptilon repens. We then compare observed locus by locus FST values with distributions of FST estimated from simulation models under expectation of neutrality. We also compare the proportion of loci possibly linked to selection and those not linked to selection which exhibit parallel trends in divergence between two community types (invaded, noninvaded). Few loci (H. comata, 2.6%; S. airoides, 8.7%) in the two native grasses may be linked to genes under the influence of selection. Also, loci linked to selection showed a greater portion of parallel trends in divergence than neutral loci. Genetic similarities between community types were less than genetic similarity within community types suggesting differentiation in response to community alteration. These results indicate that a small portion of scored AFLP loci may be linked to genes undergoing selection tied to community dominance by an invasive species. We propose that native plants in communities dominated by exotic invasives may be undergoing natural selection.

Combined Impacts of Native Grass Competition and Introduced Weevil Herbivory on Canada Thistle (Cirsium arvense)

Abstract Invading exotics typically face new competitors and an absence of specialized herbivores in their new ranges. Biological control attempts to reunite invasive weeds with coevolved herbivores and restoration can reduce the return of invaders by maximizing competition from native species. The integration of both approaches is seldom examined in detail, although the two should complement each other. We investigated the potential to suppress an important invasive plant, Canada thistle (Cirsium arvense [L.] Scop.), by integrating biological control and competition from two native grasses frequently used in rangeland restoration. We evaluated the impacts of Ceutorhynchus litura F. (Coleoptera: Curculionidae), a weevil used for Canada thistle biological control, alone and in combination with either needle and thread grass (Hesperostipa comata [Trin. & Rupr.] Barkworth) or alkali sacaton (Sporobolus airoides [Torr.] Torr.) in greenhouse competitive plantings. Weevil herbivory reduced root, but not shoot, biomass of Canada thistle. Competition from H. comata did not reduce biomass of thistles, but combinations of the weevil and H. comata greatly reduced thistle root biomass. S. airoides suppressed Canada thistle root biomass independent of weevils. Weevils had a positive indirect effect on the cool-season grass H. comata, presumably by reducing the competitive ability of thistles, but had no effect on biomass of the warm-season grass, S. airoides. Benefits of weevil presence as an augmentation of grass competition appear to depend on appropriate timing, and weevils provided the most benefit to the cool-season competitor. Our results suggest that restoration efforts can be complemented with insect biocontrol agents, although the timing of impact will depend on the particular weed species, grass competitors, and biocontrol insect agents involved.

Competitive effects of cool-season grasses on re-establishment of three weed species.

The competitive ability of five cool-season grasses relative to Dalmatian toadflax, musk thistle, and downy brome was assessed in two field studies. In 1994, Bozoisky Russian wildrye and four wheatgrass varieties (Critana thickspike, Hycrest crested, Luna pubescent, and Sodar streambank wheatgrass) were seeded into populations of downy brome and musk thistle at Riverside, WY. The same grasses were seeded into populations of Dalmatian toadflax at Cheyenne, WY, in 1995. In 1997 and 1998, weed populations at both study sites were reduced in areas seeded with the five grasses relative to unseeded controls. Hycrest crested and Luna pubescent wheatgrasses were the most competitive against the three weed species. Bozoisky Russian wildrye was more competitive against Dalmatian toadflax than against the other weeds. Sodar streambank wheatgrass suppressed musk thistle and downy brome but was not competitive against Dalmatian toadflax. Seeded grasses, such as Hycrest crested and Luna pubescent wheatgrass, appeared to limit the re-establishment of these weeds. Economic model predictions of the net present values and the internal rates of return suggest that Hycrest crested and Luna pubescent wheatgrass can provide financially feasible long-term weed control only if desired grass yields are maintained for more than 15 yr. Nomenclature: Crested wheatgrass, Agropyron cristatum (L.) Gaertn. × Agropyron desertorum Gaertn. var. ‘Hycrest’; Dalmatian toadflax, Linaria genistifolia spp. dalmatica (L.) Maire and Petitmengi #3 LINDA; downy brome, Bromus tectorum L. # BROTE; musk thistle, Carduus nutans L. # CRUNU; pubescent wheatgrass, Thinopyrum intermedium (Host. Barkworth & Dewey) Nevski var. ‘Luna’; Russian wildrye, Psathyrostachys juncea (Fisch) Nevski var. ‘Bozoisky’; streambank wheatgrass, Elymus lanceolatus (Scribn. & J. G. Smith) Gould var. ‘Sodar’; thickspike wheatgrass, Elymus macrourus (Turcz.) Tzvelev var. ‘Critana’. Additional index words: Competition, economic analysis, integrated controls, perennial grass. Abbreviations: ANOVA, analysis of variance; IRR, internal rate of return; LSD, least significant difference; NPV, net present value.

Canopy Growth and Density of Wyoming Big Sagebrush Sown with Cool-Season Perennial Grasses

Post-mining revegetation efforts often require grass seeding and mulch applications to stabilize the soils at the same time as shrub seeding, creating intraspecific competition between seeded shrubs and grasses that is not well understood. Artemisia tridentata Nutt. ssp. wyomingensis (Beetle and Young) (Wyoming big sagebrush) is the dominant premining shrub on many Wyoming mines. The Wyoming Department of Environmental Quality, Land Quality Division requires reestablishment of 1 shrub m−2on 20% of post-mined lands in Wyoming. Reclamationists seldom document the impacts of grass competition on shrub canopy size after reclamation plantings become established even though shrub canopy development is important to vegetative structural diversity. In 1999, we initiated a study at the Belle Ayr Coal Mine near Gillette, Wyoming, to evaluate the influence of grass competition on establishment and growth of Wyoming big sagebrush. Combinations of three sagebrush seeding rates (1, 2, and 4 kg pls ha−1) and seven cool-season perennial grass mixture seeding rates (0, 2, 4, 6, 8, 10, and 14 kg pls ha−1) were seeded during winter 1998–1999. Shrub density and grass cover were assessed from 1999 to 2004. We monitored sagebrush canopy size in 2001, 2002, and 2004. All sagebrush seeding rates provided shrub densities ≥1 shrub m−2 after six growing seasons. Grass production ≥75 g m−2 was achieved by seeding grasses at 6 to 8 kg pls ha−1. Canopy growth of individual sagebrush plants was least in the heaviest grass seeding rate. Reduced grass seeding rates can aid in achieving Wyoming big sagebrush density standards and enhance shrub canopy growth.

New Rangeland Residents in Wyoming? A Survey of Exurban Landowners

Abstract Rapid conversion of rural land to exurban development and the ensuing impacts on natural resources have been well-documented, but information about exurban landowners is lacking. To address this knowledge gap, we surveyed exurban landowners in six Wyoming counties and documented demographic characteristics, motivations, knowledge, and attitudes about natural resources and land management. The overall response rate was 55.6%. Generally, respondents were of retirement age, had lived in Wyoming for about 13 yr, and were raised in areas with a population < 10 000. Wyoming respondents lived in exurbia for the lifestyle and aesthetic values and did not expect economic gains from their property. Most respondents had knowledge about, and interest in, invasive species, water quality, landscaping, and gardening. More than half of respondents (54%) had never looked for information regarding land management. Information from this study can be used to strengthen the development and delivery of educational programs. Programs that focus on water quality or weed control likely will appeal to more exurban landowners than those that focus solely on grazing management. Our findings provide an accurate characterization of this audience and their motivations and attitudes regarding land management, and suggest that using a multipronged approach for outreach efforts, which includes both cost- and time-efficient ways to conduct important land management practices, might increase participation in educational programs.

Native Grasses Collected from Invasions Demonstrate Invasion Resistance

Native grasses can persist in areas dominated by invasive species, yet resistance to invasion by the selected remaining natives is largely unknown. We examine native grass lineages differing in history of survival within invasions, when transplanted into association with 2 invasive perennials. Invaded plants were collected from Russian knapweed (Rhaponticum repens) invasions, and non-invaded plants were collected outside invasions. We assess growth and reproduction of alkali sacaton (Sporobolus airoides) in the presence of Russian knapweed (the original invader) and Canada thistle (Cirsium arvense), an invasive species to which the grasses lacked exposure. On 2 field sites (Crowheart, WY and Cheyenne, WY) and in an environmentally controlled lab at the University of Wyoming, we monitored plant growth (longest leaf, basal circumference, and tiller production) of grass lineages from the 2 histories with and without the presence of the invaders. We monitored invasive species recruitment, grass seedling germination, and grass seedling establishment to determine grass fecundity and resistance to invasive encroachment. At Crowheart, when competing with Russian knapweed, invaded plants were larger than non-invaded plants, irrespective of sampling date. At Cheyenne, invaded plants competing with Canada thistle grew larger than non-invaded grasses irrespective of sampling date. In the controlled growth chamber, growth of the 2 histories differed on few dates, yet non-invaded lineages had greater leaf growth, and seedling germination was greater for invaded grasses. Lines of native grasses collected from within historic invasions display competitive growth traits in field transplants that may be useful for reclamation.

Postfire Invasion Potential of Rush Skeletonweed (Chondrilla Juncea)

Abstract North American sagebrush steppe communities have been transformed by the introduction of invasive annual grasses and subsequent increase in fire size and frequency. We examined the effects of wildfires and environmental conditions on the ability of rush skeletonweed (Chondrilla juncea L.), a perennial Eurasian composite, to invade degraded sagebrush steppe communities, largely dominated by cheatgrass (Bromus tectorum L.). Recruitment of rush skeletonweed from seed and root buds was investigated on 11 burned and unburned plot pairs on Idahos Snake River Plain following summer 2003 wildfires. Emergence from soil seedbanks was similar on burned and unburned plots in 2003 and 2004 (P  =  0.37). Soils from recently burned plots (P  =  0.05) and sterilized field soil (P < 0.01) supported greater emergence than did unburned field soils when rush skeletonweed seeds were mixed into the soils in the laboratory. These decreases may indicate susceptibility of this exotic invasive to soil pathogens present in field soils. Seeds in bags placed on field soil in late October 2003 reached peak germination by mid-January 2004 during a wet period; 1% remained viable by August 2004. Seedling emergence from sown plots or the native seedbank and establishment of new rosettes from root sprouts in 2003–2005 indicate that seed germination of rush skeletonweed on the Snake River Plain may be facultative, occurring in fall or spring if soil moisture is adequate, although many germinants may not survive. Stand development results primarily from root sprouting. Establishment from seed is episodic but provides for dispersal, with increasing fire frequency and size expanding the areas of disturbance available for new invasions.

Integrated reclamation: Approaching ecological function?

Attempts to reclaim arid and semiarid lands have traditionally targeted plant species composition. Much research attention has been directed to seeding rates, species mixes and timing of seeding. However, in order to attain functioning systems, attention to structure and process must compliment existing efforts. We ask how to use a systems approach to enhance reclamation success. Using a case study example, we discuss ways to target key drivers that return the functional and dynamic nature of western wildlands. Integration of a multitude of abiotic (soil stability, hydrology and nutrient cycling) and biotic processes (plant functional traits, species turnover and regeneration, and wildlife interactions) into reclamation planning will be crucial to uniting research with management experience. Long-term monitoring coupled with tools to unify diverse datasets will be key to future management decisions. Reclamation is constrained by our inability to unify varied experiences with documented evidence. Research should assist managers with integrating spatial and temporal variability of ecosystem processes into long-term management planning. Using an integrated approach, we can more fully comprehend reclamation within the context of ecosystem function. An integrated knowledge base should serve as a communication tool and facilitate more sustainable landscape solutions.

Establishment of Native Species in Soils From Russian Knapweed (Acroptilon Repens) Invasions

Abstract Russian knapweed (Acroptilon repens [L.] DC.), an exotic perennial forb, has invaded many native ecosystems in western North America. Russian knapweeds success is attributed to allelopathy, extensive tap rooting, zinc accumulation in soils, and a lack of North American predators. Revegetation following chemical control slows exotic reestablishment, but the impacts of Russian knapweed-invaded soils on the establishment of native forbs and shrubs have not been determined. In a greenhouse experiment, we monitored the establishment of two native forbs, Indian blanketflower (Gaillardia aristata Pursh) and purple prairie clover (Dalea purpurea Vent.) and two native shrubs, winterfat (Krascheninnikovia lanata [Pursh] A.D.J. Meeuse & Smit syn. Ceratoides lanata) and Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis [Hook.] Nutt.) in soils obtained from three Russian knapweed invasions and adjacent noninvaded areas. We analyzed soils collected near Greybull and Riverton, Wyoming, and Greeley, Colorado, for cation exchange capacity, organic matter, electroconductivity, pH, and total nitrogen, carbon, and plant-available potassium, zinc, manganese, copper, and phosphate. We documented seedling emergence of the four natives and Russian knapweed every two days for 14–17 weeks, harvested seedlings biweekly to assess their growth, and determined their zinc accumulation. All species established in invaded soil and seedlings were larger in invaded than in noninvaded soils. Invaded rangeland soils had greater organic matter (8.6% and 1.1% in invaded vs. 2.5% and 0.4% in noninvaded soils) and lower pH (7.4 in invaded versus 8.0 noninvaded soils). Zinc concentrations in invaded soils (from 0.15 to 6.56 mg · kg−1) were not high enough to limit plant growth. Reports that Russian knapweed is a hyper-accumulator of zinc are not supported by our seedling data, which suggests that previously invaded soils may not limit native seedlings.

A fuzzy logic approach to analyse the suitability of nesting habitat for greater sage-grouse in western Wyoming

Abstract Habitat suitability analysis is complex and requires integration of multiple attributes at a range of spatial scales. We use fine- and broad-scale variables within a spatial modelling framework to determine the suitability of greater sage-grouse nesting habitat using fuzzy logic. Fuzzy theory allows for a landscape component to have full, partial, or no membership in a particular management target. We used seven biophysical and anthropogenic variables correlated with nest site locations to build the fuzzy model. Using field and remotely sensed data and expert opinion, we developed fuzzy functions to define numerical membership values describing relationships between landscape characteristics and nesting habitat suitability. We used a fuzzy gamma overlay function to define five suitability classes in the resulting habitat map. Using a fuzzy logic model, we were able to spatially distinguish the suitability of nesting habitat using fine- and broad-scale attributes and characterise the uncertainty of the habitat model.