| Title |
Investigators | Department | Objectives | Approach Keywords | Progress Reports | Impact Statements | Publications | |
Project * COL00628 | |
| Title | *The Ecology of Invasive Plants |
| Investigator(s) | Brown, CS; |
| Department | Bioagricultural Sciences and Pest Mgmt. |
| Objectives | Species invasions are having major effects on ecosystems of the world and are thought to be the second leading threat to biodiversity. The research that I will conduct will focus on two primary areas of invasion ecology. First, I will conduct research to increase our knowledge of the impacts of invasive plant species and their control on resident plants and animals and the functioning of ecosystems. Second, my research will contribute to the understanding of the mechanisms responsible for the establishment of invasive species. These mechanisms may include factors that are both biotic (e.g. interactions among resident plant, animal and microbial species and between ecophysiological traits of invasive and resident plant species) and abiotic (e.g. climate and fertility). I have two main objectives in studying impacts of invasive species. The first is to learn more about the effects of changing land-use patterns, including fire and invasive species, on the hydrology of the Colorado River Watershed and the second is to investigate changes in nutrient availability and chemistry of soils, and mycorrhizal and plant communities associated with Russian knapweed (Acroptilon repens) invasions. I have three objectives in the study of mechanisms of invasion. First, I wish to develop an understanding of whether the wide ecological range of Canada thistle (Cirsium arvense) can be primarily attributed to plasticity or genetic differentiation and characterize the selection pressures acting on it in various environments. I will also study effects of fire, small scale disturbance, nutrient availability and propagule pressure on invasions in montane grasslands. Finally, I will investigate the roles of resource competition, allelopathy and changes in mycorrhizal communities in the invasion and dominance of Russian knapweed and evaluate plant community restoration approaches for Russian knapweed control and the mitigation of the negative effects it has on soils. The work that I propose to do will be useful to land managers, both public and private. It will contribute to our knowledge of the basic biology and ecology of specific invasive plant species and test general ecological theories. Understanding the impacts of invasive plant species and their control on resident plants and animals and the functioning of ecosystems will allow us to better prioritize the allocation of limited time, money and other resources for control of the most destructive invaders. Elucidating the mechanisms of invasion, the means by which exotic plants become established and increase in abundance, will provide a basis for integrated pest management controls of invasive species and tests of basic ecological theories of plant invasions |
| Approach | To study the impacts of invasive species, interviews of land managers as well as surveys of vegetation along the upper Colorado River will be conducted to identify temporal and spatial patterns of the distribution of invasive plant species that may affect hydrology. In a second set of experiments addressing impacts of invasive plants, sites dominated by Russian knapweed (Acroptilon repens) will be compared to areas with intact native vegetation. A series of experiments will be conducted to investigate the role that seeded species can play in ameliorating the soil conditions created by Russian knapweed and creating an ecological bridge for the restoration of the desired plant community. This work will also investigate the mechanisms by which Russian knapweed invades native plant communities and maintains dominance. The mechanisms of plant invasion will also be addressed in studies of Canada thistle (Cirsium arvense) collected from crop and non-crop sites within five biogeographic regions in Colorado and grown under controlled environmental conditions. In a second project, mechanisms of invasion will be studied in experiments conducted in burned and unburned montane meadows. Abundances of invasive species and their propagules will be monitored while nitrogen availability and species richnesss are manipulated. |
| Keywords | plant invasion, invasive plants, mechanisms of plant invasion, impact of invasive plants, restoration and weed control, weeds |
| Progress Reports | |
| 2003 | 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. |
| 2004 | 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. |
| 2005 | 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. |
| 2006 | 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. |
| Impact | |
| 2003 | 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. |
| 2004 | 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. |
| 2005 | 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. |
| 2006 | 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 | |
| 2006 |
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. 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. |