Author: Nicole M. DeCrappeo Publisher: ISBN: Category : Cheatgrass brome Languages : en Pages : 276
Book Description
Sagebrush steppe ecosystems in the Great Basin have become increasingly threatened by the proliferation of cheatgrass (Bromus tectorum L.), an invasive annual grass. Diverse sagebrush and perennial bunchgrass landscapes can be converted to homogenous cheatgrass grasslands mainly through the effects of fire. Although the consequences of this conversion are well understood in the context of plant community dynamics, information on changes to soil communities has not been well documented. I characterized soil surface, microbial, and nematode community dynamics in sagebrush steppe and cheatgrass-invaded areas across the northern Great Basin. I also examined how restoration treatments, such as seeding with a low impact rangeland drill and applying herbicide or sugar to plots, affected soil communities. Soil community functional diversity and structure were alike at sites where soil pH and percent bare ground were similar. Rangeland drill seeding and associated human trampling decreased biological soil crust cover at sites with high proportions of cyanobacteria. Herbicide treatments had little effect on soil communities, but addition of sugar to plots increased carbohydrate utilization and fungal biomass of cheatgrass- invaded soils. In studying paired intact and cheatgrass-invaded sagebrush plots, I found that microbial functional diversity and community composition were different in sagebrush, bunchgrass, cheatgrass, and interspace soils. Fungal biomass and species richness were highest under sagebrush and decreased under cheatgrass. To examine how soil community shifts might affect ecosystem processes, I investigated the contribution of fungi to inorganic nitrogen (N) mineralization in sagebrush and cheatgrass rhizospheres. Results from a 15N pool dilution experiment modified with the fungal protein synthesis inhibitor cycloheximide showed that gross and net N cycling rates did not differ between control sagebrush and cheatgrass soils and that fungi were important for gross NH4+ production and consumption in both soil types. However, net nitrification increased in sagebrush soils after 24 h, suggesting that when organic matter decomposition by fungi ceased bacteria became carbon limited and could no longer assimilate NH4+. These studies demonstrate that cheatgrass invasion into sagebrush steppe ecosystems can bring about significant changes to soil communities and that these changes may have repercussions for ecosystem functioning in the northern Great Basin.
Author: Rachel Oglevie Jones Publisher: ISBN: Category : Electronic books Languages : en Pages : 318
Book Description
Invasion by non-native species is a serious ecological threat and the susceptibility of ecosystems to invasion is often highly correlated with soil resource availability. Understanding the role of plant-soil feedbacks in invaded ecosystems could provide insight into community successional trajectories following invasion and could improve our ability to manage these systems to restore native diversity. My dissertation examined how plant-soil feedbacks and resource availability influence the success of both cheatgrass and native species with three interrelated studies. In a large-scale observational study, I evaluated plant community characteristics as well as soil and plant nutrients associated with progressive cheatgrass invasion in a broadly distributed sagebrush ecological site type. I found that although many nutrient pools did not differ among levels of invasion, soil ammonium (NH4+) was negatively affected by increases in cheatgrass cover. Also, cheatgrass nutrient content did not differ across sites indicating that cheatgrass may alter plant available soil nutrients to the detriment of competitors while maintaining its own nutritional content via high nutrient use efficiency and/or soil mining. I also conducted a field experiment to provide a more mechanistic understanding of the role of disturbance on nutrient availability and invasion and to address potential management approaches. I evaluated the effects of 4-5 years of repeated burning, in combination with litter removal and post-fire seeding, on nutrient dynamics and plant responses. Results from my field experiment indicated that repeated burning is unlikely to decrease soil N availability in cheatgrass-dominated systems due to cool fire temperatures that do not volatilize biomass N and strong effects of weather on plant growth and soil processes. Repeated burning and litter removal, however, did have negative effects on litter biomass and C and N contents which negatively influenced cheatgrass biomass, density and reproduction. In addition, post-fire seeding with common wheat decreased cheatgrass abundance, likely due to competition. Integrated restoration approaches that decrease litter biomass and seed banks and increase competitive interactions may be more effective at reducing annual grasses and establishing desirable perennial species than approaches aimed at reducing soil nutrients. Together, the observational and experimental components of my dissertation indicate that plant-soil feedbacks in arid sagebrush shrublands are complex and that understanding these feedbacks requires both spatial and temporal variability in sampling. Furthermore, the results from these studies provide valuable information on techniques that could facilitate the restoration of cheatgrass-dominated systems to more diverse plant communities.
Author: Michael D. Reisner Publisher: ISBN: Category : Languages : en Pages : 540
Book Description
Sagebrush steppe ecosystems are one of the most widespread but endangered ecosystems in North America. A diverse array of human-related stressors has gradually compromised these ecosystems' resilience to disturbance and invasion by Bromus tectorum (cheatgrass). The role of the foundational shrub Artemisia as a driver of herbaceous community structure and dynamics during this degradation process is poorly understood. Many of the individual factors driving B. tectorum invasions are well documented. However a predictive understanding of the relative importance of complex, interacting factors in the causal network of simultaneously occurring processes determining invasibility has proven elusive. I examined these issues at the landscape level across 75 sites capturing a range of soil and landscape properties and cattle grazing levels similar to those found across the Great Basin. Cumulative cattle herbivory stress levels were a predominant component of both the overlapping heat and water stress gradients driving the structure of Artemisia interactions with herbaceous species. Consistent with the stress gradient hypothesis, Artemisia facilitation of herbaceous species was most frequent and strongest at the highest stress levels, and competition was most frequent and strongest at the lowest stress levels. The two species with the highest competitive response abilities, Elymus elymoides and Poa secunda, showed the strongest facilitation at the upper limits of their stress tolerances. The structure of Artemisia interactions with the invasive B. tectorum was strikingly different than those with native bunchgrasses. Artemisia interactions with native bunchgrasses shifted from competition to facilitation with increasing heat, water, and herbivory stress, but its interactions remained competitive with B. tectorum along the entire stress gradient. Shifts in the structure of interactions between Artemisia and native bunchgrasses were associated with both an increase and decrease in community compositional and functional stability. I report the first evidence of native species facilitation decreasing community invasibility. Artemisia facilitation increased native bunchgrass composition, which reduced the magnitude of B. tectorum invasion in under-shrub compared to interspace communities. This decreased invasibility did not translate into lower invasibility at the community level because of the limited spatial scale over which such facilitation occurs. Artemisia facilitation increased community compositional and functional stability at intermediate stress levels but decreased community stability at high stress levels. Facilitation became a destabilizing force when native bunchgrass species became "obligate" beneficiaries, i.e. strongly dependent on Artemisia facilitation for their continued persistence in the community. Structural equation modeling assessed the structure of the causal network and relative importance of factors and processes predicted to drive community invasibility. The linchpin of ecosystem invasibility was the size of and connectivity between basal gaps in perennial vegetation, driven by shifts in the structure and spatial aggregation of the native bunchgrass community. Landscape orientation and soil physical properties determined inherent risk to invasion. Resident bunchgrass and biological soil crust communities provided biotic resistance to invasion by reducing the size of and connectivity between basal gaps and thereby limiting available resources and reducing safe sites for B. tectorum establishment. High levels of cattle grazing reduced ecosystem resilience by reducing native bunchgrass and biological soil crust abundance and altering bunchgrass community composition and facilitated B. tectorum invasion. Conserving and restoring resilience and resistance of these imperiled ecosystems will require reducing cumulative stress levels. As global climate change increases heat and water stress, reducing cumulative cattle grazing intensities by altering utilization rates and/or seasons of use may be the only effective means of accomplishing these goals.
Author: Kyle A. Taylor Publisher: ISBN: 9781339440484 Category : Big sagebrush Languages : en Pages :
Book Description
Big sagebrush (Artemisia tridentata) ecosystems have experienced loss over large portions of their historic range throughout the intermountain western United States over the last two centuries. Leading into the 21st century, much of this loss could be attributed to anthropogenic land conversion -- particularly from regional population growth, agricultural development, and the spread of invasive species. Over the course of the 21st century, climate change and invasive grassland conversion (Bromus tectorum) are expected to further alter the structure of regional sagebrush ecosystems, potentially contributing to range loss for big sagebrush and its many obligate species. My overall objective was to investigate the exposure of sagebrush ecosystems to risks from climate change and invasive species spread. I developed a series of species distribution models (SDMs) for three major sagebrush subspecies and compare the trajectory of regional sagebrush ecosystems under future climate conditions. I assessed my confidence in range projections for big sagebrush under future climate conditions using a sensitivity analysis to explore deficiencies in the underlying data behind my SDMs. Lastly, I attempted to assess the invasibility of climatically-stable sagebrush ecosystems by developing and deploying a process-based demographic model for cheatgrass at sites throughout the intermountain region. I implemented a series of big sagebrush species distribution models (SDMs) fit to individual subspecies records of big sagebrush. I used climate variables previously described as limiting for big sagebrush as explanatory data and extrapolate the models into mid-century and end-of-century conditions using an ensemble of recent global circulation model (GCM) data. I expected all three big sagebrush subspecies to respond negatively to increases in temperature and drier summer conditions forecasted for much of the intermountain region, assuming that future environmental conditions would warm beyond the environmental tolerances to which big sagebrush is physiologically adapted to. However, at the subspecies level, this did not appear to be the case. Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and basin big sagebrush (Artemisia tridentata ssp. tridentata) both demonstrated slight range expansion, largely along elevational gradients, under end-of-century forecasts across GCMs. Although experiencing loss within southern portions of their current range, the warmer winter conditions and slightly drier summer conditions forecasted for wyomingensis and tridentata are not so unusual that the subspecies don’t currently encounter these conditions within portions of their current range. Notably, mountain big sagebrush (Artemisia tridentata ssp. vaseyana) does respond negatively to future climate conditions, with winter temperatures increasing beyond what the subspecies experiences across its current range. Unlike ssp. tridentata and wyomingensis, vaseyana does not appear to have a large elevational gradient to retreat into under future climate conditions, which could result in potentially large losses of its current range if the subspecies is unable to adapt and compete under warmer conditions. In order to better indicate confidence in SDM predictions for big sagebrush, I used a Monte Carlo-based sensitivity analysis to demonstrate how uncertainties attributed to occurrence, absence, and climate data biases propagate through two commonly used SDM algorithms (Generalized Linear Models [GLMs] and Random Forests [RF]) for sagebrush ecosystems dominated by ssp. wyomingensis and tridentata. I derived predictive intervals for both GLM and RF and used the intervals to produce envelopes indicating areas of high and low predictive confidence in SDM predictions and explore how bias can contribute to latitudinal and elevational drift in suitability predictions. Both algorithms demonstrated sensitivities to climate and presence-record uncertainty that translated to large geographic uncertainty in predictions. I found that RF is more sensitive to bias than GLM, and that climate and presence record bias contributed to greater predictive ambiguity than absence record uncertainty. I found that uncertainties in predictions arising from data uncertainty could easily produce the same magnitude of range shift as those observed under mid-century (2050) predictions of distributional change for big sagebrush under climate change, suggesting that mid-century forecasts of change for big sagebrush are not so unusual that they couldn’t also be explained by biases affecting underlying data. However, many late-century (2100) predictions of suitability change appear to diverge from what was observed in our sensitivity analysis and deserve greater confidence. As roughly half of climatically suitable space available to big sagebrush throughout the intermountain region has experienced some degree of invasion by cheatgrass, it’s continued spread is an important factor to consider in assessing the long-term viability of big sagebrush ecosystems. Using a soil hydrology model (SOILWAT) and a meta-analysis conducted from a number of studies of cheatgrass’ demography and physiology, I built a process-based model that simulates cheatgrass population growth over time. I applied the model to current climate conditions at a number of sites sampled from sagebrush ecosystem subspecies strata across the intermountain region and found detectable differences in population suitability response. The cheatgrass demographic model demonstrates detectable differences in population response between montane sites (suitable for ssp. vaseyana) and basin sites (suitable for ssp. wyomingensis and tridentata) that suggest basin subspecies ranges are more suitable for cheatgrass than montane sites. I also demonstrate that basin subspecies are typically closer to known invasive annual grasslands throughout the intermountain region, and are probably more susceptible to cheatgrass propagule pressure. A synthesis of results across my studies suggests differing fates for regional sagebrush ecosystems. Although ssp. wyomingensis and tridentata dominated sagebrush ecosystems may be potentially robust to future climate change, they demonstrate a greater risk to cheatgrass invasion, which could challenge the long-term stability of sagebrush ecosystems in the basin interior of the intermountain region. Conversely, although montane sagebrush ecosystems dominated by ssp. vaseyana may be at comparatively less risk of cheatgrass invasion, these sagebrush ecosystems will face greater exposure to climate change stressors over the course of the 21st century.
Author: Lea A. Condon Publisher: ISBN: Category : Cheatgrass brome Languages : en Pages : 118
Book Description
We are at risk of losing the sagebrush steppe in the floristic Great Basin to the invasion of Bromus tectorum L., cheatgrass. The floristic Great Basin includes the Central Basin and Range, the Northern Basin and Range, and the Snake River Plain. The Great Basin receives most of its precipitation as winter snow and experiences hot and dry summers. Early accounts of invasion by cheatgrass associated it with farming and grazing practices. The non-farmed areas in the region are still actively grazed and referred to as rangelands. On invaded sites, cheatgrass changes the flammability of fuels on invaded landscapes, across the Great Basin, from coarser fuels that are widely spaced to fine fuels that are continuous, filling interspaces between perennial plants. The fuel load created by cheatgrass regenerates annually. This has resulted in a change in the fire regime of the Great Basin from infrequent, small fires to more frequent large fires. In arid lands globally, soil interspaces between perennial plants are typically filled by biological soil crusts (biocrusts). This is also true for ecoregions in and surrounding the Great Basin. Biocrusts are known to influence many ecosystem processes that cheatgrass influences, specifically nutrient cycling and availability of soil moisture. However, little work has been done on biocrusts of the Great Basin and to my knowledge, no one had restored biocrusts within the Great Basin. I attempt to fill some of this knowledge "interspace" by relating biocrust presence to disturbances and cheatgrass invasion and to demonstrate the potential for biocrust restoration within this region. Previous work in eastern Oregon demonstrated relationships between declines in biocrusts and increases in cheatgrass with increasing grazing intensity, soil temperature, and decreasing soil moisture. Grazing intensity influences the cover of biocrusts as well as the abundance and composition of native bunchgrasses. Native bunchgrasses influence the interspace gap size between perennial herbaceous vegetation which is directly associated with the cover of cheatgrass. In a region where grazing records may be incomplete and may exist in various forms of data, having a simple indicator of grazing impacts would be useful. It is also crucial that we have an understanding of what leads to loss of site resistance to cheatgrass. This previous work suggested that cover of biocrusts, in addition to bunchgrass composition, were associated with increased site resistance to cheatgrass. In Chapter 2, I used current grazing records from a range of suspected grazing intensities, to examine the ability of both biocrusts and perennial vegetation to maintain site resistance to cheatgrass after fire. I examined the ability of mosses and lichens to maintain site resistance separately given that these are two very different kinds of organisms. Mosses are non-vascular plants and early colonizers of sites in primary succession. Lichens have a symbiotic relationship between a fungus and a photosynthesizing partner, a cyanobacteria, an algae or both. Using structural equation models, I corroborated that perennial vegetation and lichens are associated with increased site resistance to cheatgrass and that mosses are associated with and may facilitate both lichens and perennial herbaceous vegetation. Also in Chapter 2, I identified that burned sites were associated with increased grazing pressure by livestock as shown by increases in cow dung density and increases in gap size between perennial herbaceous vegetation. The Great Basin is managed for cover of perennial vegetation but it could also be managed for morphogroups of biocrusts. Considering morphogroups of biocrusts, which were shown in the Chapter 2 to be important for site resilience and resistance, I wanted to determine if there were site characteristics associated with biocrust distribution and recovery from disturbance, across the Great Basin. Outside of the Great Basin on the Columbia Plateau, others had found that mosses were still present on disturbed sites whereas lichens were often lost. In addition, biocrust species were more associated with soil properties than with grazing by livestock. Given that grazing by livestock and fire are common disturbances across the region, I wanted to know if the same relationships between biocrusts, soil properties and disturbance were true in the Great Basin. I found that cover of the lichen component of biocrusts was higher on sites that were both ungrazed and unburned. Factors related to disturbance characteristics were correlated with the recovery of biocrusts, even after accounting for time since fire. Factors related to disturbance, a composite of grazing and fire, were more important for structuring the cover and composition of morphogroups as opposed to environmental conditions. Lichens were the most sensitive morphogroup, compared to tall mosses, followed by short mosses which were favored by some disturbance but reduced in cover immediately after fire. Perennial grasses were also favored by some disturbance and perennial forbs did not show an obvious relationship with a disturbance gradient. Chapter 3 highlights that grazing by livestock and fire are common disturbances across the region so much so that the effects of one on the abundances of morphogroups could not be separated from the other. Given the observed contributions of biocrusts to site resilience and resistance, I wanted to know if we could restore biocrusts in the field. Others have grown mosses in a lab setting but this was the first study to restore mosses in the Great Basin. I tested the influence of factors that are commonly used in the field of restoration for facilitating plant establishment. I tested the influence of season of inoculation (fall versus spring), the addition of organic matter (in the form of jute net), irrigation (in the spring season) and the climatic setting of moss the collection sites (for moss propagation), in comparison to the experiment site (warm, dry versus cool, moist) on moss growth. I used two moss species: a ruderal (Bryum argenteum) and a later successional species (Syntrichia ruralis). Moss cover increased when the climatic setting of the collection site matched the experiment site. Mosses were facilitated by the addition of the organic jute netting, putting on most of their growth in winter. Although there is still a great deal of work to be done developing moss material for restoration and working out inoculation rates of moss fragments, similar to seeding rates, land managers have another tool to consider when rehabilitating sites after disturbance. Managing the Great Basin for biocrusts in the presence of grazing and fire will not only increase site resistance to cheatgrass but it will add to the conservation of ecosystem functions related to nutrient cycling, hydrologic cycling and soil erosion. Site resistance will be improved with increased periods of rest from grazing following fire. The lichen component of biocrusts is a more sensitive indicator of disturbance when compared with mosses or perennial vegetation but we are currently actively managing for perennial vegetation and not biocrusts. The moss component of biocrusts can be successfully restored in the Great Basin, without irrigation. This dissertation shows that land managers should consider a suite of organisms, in addition to perennial plants to achieve management goals and maintain site resistance to cheatgrass.
Author: Matthew J. Germino Publisher: Springer ISBN: 3319249304 Category : Technology & Engineering Languages : en Pages : 475
Book Description
Invasions by exotic grasses, particularly annuals, rank among the most extensive and intensive ways that humans are contributing to the transformation of the earth’s surface. The problem is particularly notable with a suite of exotic grasses in the Bromus genus in the arid and semiarid regions that dominate the western United States, which extend from the dry basins near the Sierra and Cascade Ranges across the Intermountain Region and Rockies to about 105° longitude. This genus includes approximately 150 species that have a wide range of invasive and non-invasive tendencies in their home ranges and in North America. Bromus species that became invasive upon introduction to North America in the late 1800’s, such as Bromus tectorum and B. rubens, have since became the dominant cover on millions of hectares. Here, millenia of ecosystem development led to landscapes that would otherwise be dominated by perennial shrubs, herbs, and biotic soil crusts that were able to persist in spite of variable and scarce precipitation. This native ecosystem resilience is increasingly coveted by land owners and managers as more hectares lose their resistance to Bromus grasses and similar exotics and as climate, land use, and disturbance-regime changes are also superimposed. Managers are increasingly challenged to glean basic services from these ecosystems as they become invaded. Exotic annual grasses reduce wildlife and livestock carrying capacity and increase the frequency and extent of wildfi res and associated soil erosion. This book uses a unique ecoregional and multidisciplinary approach to evaluate the invasiveness, impacts, and management of the large Bromus genus. Students, researchers, and practitioners interested in Bromus specifically and invasive exotics in general will benefit from the depth of knowledge summarized in the book.
Author: Nicole M. DeCrappeo
Author: Rachel Oglevie Jones
Author: Michael D. Reisner
Author: Ann L. Hild
Author: Kyle A. Taylor
Author: Lea A. Condon
Author: 
Author: Alexandra D. Reinwald
Author: 
Author: Matthew J. Germino