Progress 07/01/03 to 06/30/07
Outputs
OUTPUTS: Bromus tectorum (cheatgrass, downy brome), one of the most pervasive weeds in rangeland of the U.S., reduces native species diversity and transforms habitats. It has increased fire frequencies and intensities in the Great Basin, resulting in loss of shrubs and perennial grasses, which are valuable livestock grazing resources and wildlife habitat. Bromus has been reported to be increasing in abundance at high elevations, creating concern among land managers because of the potential for loss of critical wildlife winter range and livestock grazing resources. During the course of this project, numerous experiments were conducted and analyzed, and the results have been extended to the scientific community and public through papers and presentations. The project outputs include at least six talks at scientific meetings, five invited scientific presentations on campus, 11 invited presentations off campus, seven publications in peer-reviewed journals, and two publications for the
lay public.
PARTICIPANTS: Dr. Ruth Hufbauer was an important collaborator on the molecular genetics aspects of this research project, and the National Park Service was an important partner organization. One doctoral student and one masters student completed their degrees.
TARGET AUDIENCES: The target audience for this project includes the scientific community and land managers, both public and private, who are interested in prevention, management and impacts of invasive plants. University students comprise an important target audience.
Impacts
We conducted experiments to evaluate whether locally adapted genotypes could be the reason for the reported increase in Bromus at high elevations. Preliminary studies indicated that germination patterns of populations from low and high elevations differed. Subsequent common garden studies, and evaluation of neutral genetic variation indicated variation among sites and individuals, but not between low and high elevation populations. Our results suggest that the success of Bromus is not due to a few general-purpose genotypes, but rather many genotypes associated with many different phenotypes. We also conducted a series of experiments to better understand Bromus ecology and evaluate control and restoration strategies. We measured the responsiveness of six native plants and Bromus to field and commercial sources of arbuscular mycorrizal fungi (AMF) inoculum. Bromus tectorum and early successional plant species were negatively responsive and late successional species were
positively responsive to field AMF inoculum, while commercial inoculum was ineffective. We compared mycorrhizal inoculum potential of field soils from beneath native plants surrounded by Bromus and the same species surrounded by native vegetation. We found that Bromus was associated with diminished AMF. Next we tested responses of two native plant species when grown in soils trained by Bromus in a greenhouse. Results indicated that Bromus did not directly affect the AMF community compared with other native plants. To address decreased AMF found associated with Bromus soils, we conducted a field experiment that included AMF, sucrose additions, and native seed applications to improve native species growth and establishment. Sucrose reduced both Bromus and other annual plant species abundance and richness. Although field soil inoculums reduced Bromus, it did not appear to increase native perennial species. In a second field experiment, we reduced Bromus cover to less than 5% with
glyphosate and added different seed mixtures based on successional models of tolerance and facilitation. This tested an ecological bridge approach in which early successional species replace invasive species and allow succession to proceed. Late successional plant species established marginally better in the facilitation model treatment. The native plant species included may have been marginally effective at forming an ecological bridge for other late successional species, but none of the seeding treatments inhibited Bromus re-invasion. This project improved our understanding of the mechanisms behind the success of Bromus, and enhanced our knowledge of basic evolutionary and ecological processes. The methods tested provide a basis for improved management of Bromus, and restoration of habitats it invades. The information learned has been disseminated to the target audience through scientific presentations and publications as well as classroom teaching activities.
Publications
- Rowe, H.I. 2006. Investigations of Bromus tectorum: Restoration strategies and interactions with arbuscular mycorrhizal fungi. Ph.D. Thesis. 102 pages. Colorado State University.
- Brown, C.S. 2004. Are functional guilds more realistic management units than individual species for restoration? Weed Technology 18:1566-1571.
- Brown, C.S., and Rowe, H.I. 2004. The unwelcome arrival of Bromus tectorum to high elevations. Proceedings High Altitude Revegetation Workshop No. 16, March 2004, Fort Collins, Colorado. Colorado Water Resources Research Institute Information Series No. 99. W.R. Keammerer and J. Todd, eds.
- Fargione, J., Brown, C.S., and Tilman, D.. 2003. Community assembly and invasion: An experimental test of neutral versus niche processes. Proceeding of the National Academy of Sciences 100:8916-8920.
- Rowe, H.I., Brown, C.S., and Paschke, M.W. 2008. The influence of soil inoculum and nitrogen availability on restoration of high elevation steppe communities invaded by Bromus tectorum. Restoration Ecology.
- Sher, A., Gieck, S., Brown, C.S., Nissen, S. 2008. Cheatgrass invasion following tamarisk control and restoration-related disturbances. Restoration Ecology.
- Freeman, J.P., Stohlgren, T.J., Hunter, M.E., Omi, P.N., Martinson, E.J., Chong, G.W., and Brown, C.S. 2007. Rapid Assessment of Post-Fire Plant Invasions in Coniferous Forests of the Western U.S. Ecological Applications 17:1656-1665.
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Progress 01/01/06 to 12/31/06
Outputs
Non-native plant species can change the functioning of ecosystems in many ways. Bromus tectorum (cheatgrass, downy brome), an invasive annual grass species, has been shown to increase fire frequencies and intensities in the Great Basin. This has resulted in the loss of shrubs and perennial grasses, which are valuable livestock grazing resources and wildlife habitat. This species is now the most ubiquitous weed in steppe vegetation in Western North America, and its dominance directly affects our ability to sustain ranching, forestry, and rural communities. The purpose of this research is to develop effective control and mitigation techniques to restore montane habitats invaded by cheatgrass through increasing our understanding of the interactions between cheatgrass, native plant species, and the soil microbial community, especially arbuscular mycorrhizal fungi (AMF). Non-native plant species may alter arbuscular mycorrhizal fungi (AMF) communities in ways that benefit
themselves in competitive relationships. B. tectorum invasion is associated with shifts in AMF community composition. We compared the soil mycorrhizal inoculation potential in the root zones of natives in a disturbed area when surrounded by B. tectorum or an undisturbed area with native plants in the field. To distinguish whether the decrease in AMF propagules was a function of disturbance or B. tectorum, we conducted a second experiment. We examined the effect of planting B. tectorum or one of three native plant species on AMF and subsequent target plant growth in the greenhouse. In the greenhouse, target plant biomass and AMF colonization were not different in B. tectorum trained soils than soils trained with the native plants. These results suggest that correlations between B. tectorum and depauperate AMF communities in the field may be caused by indirect B. tectorum effects or disturbance.
Impacts
The invasive, annual grass Bromus tectorum (cheatgrass, downy brome) is a widespread problem in Colorado and is increasing in abundance at high elevations. Cheatgrass increases the frequency and intensity of fire, competes with native vegetation and alters soil microbial communities. It can compromise valuable grazing land for livestock and winter habitat for wildlife in montane areas. This research will help land managers effectively restore native plant communities and reduce the abundance of cheatgrass in invaded montane habitats.
Publications
- H.I. Rowe, C.S. Brown, and V. Claassen. 2007. Comparisons of mycorrhizal dependency with field soil and commercial inoculum for seven native montane species and Bromus tectorum. Restoration Ecology 15:44-52.
- C. S. Brown and R. A. Hufbauer. 2006. A growing problem? Bromus tectorum (cheatgrass, downy brome) in Rocky Mountain National Park. Rocky Mountain Nature Association Quarterly, Spring 2006. Rocky Mountain Nature Association, Estes Park, Colorado, USA.
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Progress 01/01/05 to 12/31/05
Outputs
Bromus tectorum (cheatgrass, downy brome) is a problematic invasive annual grass species that has large impacts on plant communities and ecosystems. It has been implicated in increasing fire frequencies and intensities, which has resulted in its replacement of shrubs and perennial grasses, becoming the most ubiquitous weed in steppe vegetation in Western North America. The invasion of cheatgrass into high elevation sites throughout the west is a key problem that directly affects our ability to sustain ranching, forestry, and rural communities. Managers are concerned about losing valuable winter habitat for wildlife and grazing land for livestock in montane regions due to the invasion of cheatgrass. The purpose of this research is to develop effective control and mitigation techniques to restore montane habitats invaded by cheatgrass through increasing our understanding of the interactions between cheatgrass, native plant species, and the soil microbial community,
especially arbuscular mycorrhizal fungi (AMF). In low nutrient environments, late-successional species with more dependence on AMF can take advantage of mycorrhizal associations to extract scarce resources and gain a competitive edge over early-successional species such as cheatgrass. Mycorrhizae are ubiquitous and easily colonize sites, thus the addition of mycorrhizal inoculum is generally not required. However, mycorrhizal inoculation may increase the competitive ability of highly mycorrizal dependent, late-successional plants in low nutrient environments. Two factorial greenhouse experiments were conducted to compare biomass of plant species with and without field soil and commercial inoculum treatments along a phosphorus (P) gradient, which ranged from ambient field levels to 12% of field levels, using dilutions of native soils. The two field soil inoculum treatments resulted in significant biomass differences for all species studied. Late-successional species responded
positively to field inoculum, whereas, early-successional species responded negatively. The two commercial inocula had a low colonization rate (14 out of 166 inoculated plants). The commercial inocula substrates had significant treatment effects on five of the seven species included in the study in the apparent absence of mycorrhizal symbiosis. Soil P levels influenced mycorrhizal responsiveness in only one species, Aster laevis. Our results show that, at least for the species studied here, locally collected field inoculum is the best choice for re-establishment of late successional, native plant species. The implications of these results for management include: (1) Locally collected field inoculum is more effective than commercial inoculum for establishing late successional plant species, (2) Native species tend to respond better to commercial inocula that contain higher AM fungal species diversity compared with commercial single species inoculum, (3) AM fungal inoculation should not
increase the spread of cheatgrass, (4) For many perennial native species, AM fungi may improve establishment and growth of native plant species regardless of the soil P levels.
Impacts
Montane regions in the West are being invaded by cheatgrass, an invasive annual grass that has large negative effects on plant communities and ecosystems. Cheatgrass increases the frequency and intensity of fire, competes with native vegetation and alters soil microbial communities. It can compromise valuable grazing land for livestock and winter habitat for wildlife in montane areas. This research will help land managers effectively restore native plant communities and reduce the abundance of cheatgrass in invaded montane habitats.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Invasion of Bromus tectorum (cheatgrass, downy brome) into high elevation sites throughout the intermountain west is a key problem that directly affects our ability to sustain ranching, forestry, and rural communities. Cheatgrass is a problematic invasive annual grass species that has large impacts on plant communities and ecosystems. It has been implicated in increasing fire frequencies and intensities, which has resulted in its replacement of shrubs and perennial grasses, becoming the most ubiquitous weed in steppe vegetation in Western North America. Managers are concerned about losing valuable winter habitat for wildlife and livestock in montane regions due to the invasion of cheatgrass. The control of cheatgrass and restoration of plant communities that it invades continue to be major challenges for land managers. The purpose of this research is to develop effective control and mitigation techniques to restore montane habitats invaded by cheatgrass. In low
nutrient environments, late-successional species with more dependence on abuscular mycorrhizal fungi (AMF) can take advantage of mycorrhizal associations to extract scarce resources and gain a competitive edge over early-successional species such as cheatgrass. Sucrose addition has been an effective treatment to reduce nitrogen (N) levels in soils and shift community composition from annual to perennial species. Mycorrhizae are ubiquitous and easily colonize sites, thus the addition of mycorrhizal inoculum is generally not required and has not been tested in combination with the sucrose treatments. However, AMF communities can be depressed in cheatgrass dominated communities, thus, supplementation of naturally occurring AMF spores may be necessary for optimal establishment and growth of native plant species. Mycorrhizal inoculation may increase the competitive ability of highly mycorrizal dependent, late-successional plants in the low nutrient environment created by sucrose addition.
In this study, native species that were dependent on AMF in greenhouse studies demonstrated improved emergence early in the growing season (July) in plots that received AMF inoculum compared to plots that did not (P = 0.007). The emergence of other seeded species caught up to the AMF dependent species by August (effect of AMF P = 0.73), probably due to the favorable rainfall patterns in the summer of 2004. However, the early-season boost to AMF dependent, late-successional species provided by the addition of AMF inoculum may be essential to optimal performance of these species in dry years. Emergence of early-successional species that were seeded into plots was lower when sugar was added as a carbon source that reduces N availability (P = 0.002, 0.03 in July and August, respectively), whereas, the late-successional species were not affected by sugar addition (P = 0.24, 0.16 in July and August, respectively). These results indicate that addition of AMF and sugar may be used as tools to
encourage desirable, late-successional species and discourage early-successional species like cheatgrass. The findings will help develop safe, effective, economical and thus, sustainable, control and restoration strategies.
Impacts
Cheatgrass is an invasive annual grass that has large negative effects on plant communities and ecosystems through increasing the frequency and intensity of fire, competing with native vegetation and altering soil microbial communities. It may be compromising valuable winter habitat for wildlife and livestock in montane areas which it invades. This research develops tools for the safe, effective, economical and sustainable control of cheatgrass and restoration of the sites it invades, which are critical to minimizing and reversing its negative effects.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
The purpose of this project is to gain an understanding of the mechanisms underlying the expanding range of Bromus tectorum L. (cheatgrass, downy brome) to high elevation sites. Land managers report that cheatgrass now occurs at elevations where it did not occur in the past. Cheatgrass is a problematic invasive annual grass species that has large impacts on plant communities and ecosystems. It has been implicated in increasing fire frequencies and intensities, which has resulted in its replacement of shrubs and perennial grasses, becoming the most ubiquitous weed in steppe vegetation in Western North America. Managers are concerned about losing valuable winter habitat for wildlife due to the invasion of cheatgrass and its ability to out-compete native vegetation and to increase fire frequency and intensity. This study evaluates the potential for local adaptation to high elevation habitats to be the underlying cause of the range expansion of cheatgrass. Summer
precipitation is less reliable at low elevations than at high elevations that get daily thunder storms. Thus seeds at low elevations that germinate in the summer may be less likely to complete their life cycle than those at high elevations, a strong selection pressure against summer germination in low elevation sites. Seeds from low elevation populations may need to receive environmental cues that winter is approaching in order to germinate. If so, populations from the low-elevation sites should have faster and higher germination rates after pre-chilling and without light (simulating winter conditions) than seeds from high-elevation sites due to the selective forces exerted by climate in the respective regions. In this study, seeds of cheatgrass were collected from 12 sites along an elevation gradient. Seeds were placed on moist germination paper and either chilled at 2 degrees C for 10 days before initiating the experiment or not pre-chilled. Pre-chilled and non-chilled seeds were
placed in one of two growing conditions: light for 8 hours each day or no light. Germination over time of seeds from different populations depended on whether or not they were pre-chilled (p < 0.0001). Germination rates slowed with pre-chilling for the highest elevation site and two of the mid-elevation sites, whereas, the rate of germination of seeds from the second highest site increased with pre-chilling. The germination over time of seeds from different populations also depended on which light treatment they received (p=0.02). Light increased the speed of germination of the second highest elevation site and one mid-elevation site, whereas, light made no difference to germination rates of the highest elevation site and another mid-elevation site. Although the original expectations were not supported and elevation alone cannot explain the variation measured, the results suggest that the populations differ and there is potential for local adaptation to have occurred.
Impacts
Cheatgrass is an invasive annual grass that has large negative effects on plant communities and ecosystems through increasing the frequency and intensity of fire, competing with native vegetation and altering soil microbial communities. Cheatgrass has begun to invade high elevation sites in the last two decades. Understanding the mechanisms that have allowed this range expansion is essential to determine what management actions will be most effective for controlling cheatgrass in high elevation habitats and preventing future invasions.
Publications
- No publications reported this period
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