Browsing Rangeland Ecology & Management, Volume 67, Number 4 (July 2014) by Title
Now showing items 8-11 of 11
Natural regeneration processes in big sagebrush (Artemisia tridentata)Big sagebrush, Artemisia tridentata Nuttall (Asteraceae), is the dominant plant species of large portions of semiarid western North America. However, much of historical big sagebrush vegetation has been removed or modified. Thus, regeneration is recognized as an important component for land management. Limited knowledge about key regeneration processes, however, represents an obstacle to identifying successful management practices and to gaining greater insight into the consequences of increasing disturbance frequency and global change. Therefore, our objective is to synthesize knowledge about natural big sagebrush regeneration. We identified and characterized the controls of big sagebrush seed production, germination, and establishment. The largest knowledge gaps and associated research needs include quiescence and dormancy of embryos and seedlings; variation in seed production and germination percentages; wet-thermal time model of germination; responses to frost events (including freezing/thawing of soils), CO2 concentration, and nutrients in combination with water availability; suitability of microsite vs. site conditions; competitive ability as well as seedling growth responses; and differences among subspecies and ecoregions. Potential impacts of climate change on big sagebrush regeneration could include that temperature increases may not have a large direct influence on regeneration due to the broad temperature optimum for regeneration, whereas indirect effects could include selection for populations with less stringent seed dormancy. Drier conditions will have direct negative effects on germination and seedling survival and could also lead to lighter seeds, which lowers germination success further. The short seed dispersal distance of big sagebrush may limit its tracking of suitable climate; whereas, the low competitive ability of big sagebrush seedlings may limit successful competition with species that track climate. An improved understanding of the ecology of big sagebrush regeneration should benefit resource management activities and increase the ability of land managers to anticipate global change impacts. © 2014 The Society for Range Management.
Of grouse and golden eggs: Can ecosystems be managed within a species-based regulatory framework?Declining greater sage-grouse populations are causing concern for the future of this species across the western United States. Major ecosystem issues, including exotic annual grass invasion and conifer encroachment, threaten vast acreages of sagebrush rangeland and are primary threats to sage-grouse. We discuss types of problems facing sage-grouse habitat and argue that complex ecosystem problems may be difficult to address under the Endangered Species Act as currently applied. Some problems, such as anthropogenic development, can be effectively regulated to produce a desired outcome. Other problems that are complex and involve disruption of ecosystem processes cannot be effectively regulated and require ongoing commitment to adaptive management. We believe that historical inertia of the regulatory paradigm is sufficient to skew management toward regulatory mechanisms, even though complex ecosystem problems impact large portions of the sage-grouse range. To overcome this situation, we suggest that the regulatory approach embodied in the Endangered Species Act be expanded to include promoting management trajectories needed to address complex ecosystem problems. This process should begin with state-and-transition models as the basis for a conceptual framework that outlines potential plant communities, their value as sage-grouse habitat, and their ecological status. Desired management trajectories are defined by maintenance of an ecologically resilient state that is of value as sage-grouse habitat, or movement from a less desired to a more desired state. Addressing complex ecosystem problems will involve shifting conservation roles. Under the regulatory approach, programmatic scales define regulatory policies, and local scales focus on implementing those policies. With complex ecosystem problems, programmatic scales empower local conservationists to make decisions necessary to adaptively manage problems. Putting ecosystem management on par with traditional regulatory actions honors obligations to provide regulatory protections while maintaining the capacity of the ecosystem to produce habitat and greatly expands the diversity of stakeholders willing to participate in sage-grouse conservation. © 2014 The Society for Range Management.
Plant community response following removal of Juniperus virginiana from tallgrass prairie: Testing for restoration limitationsWoody plant encroachment in natural grasslands is a widely documented global phenomenon that alters ecosystem dynamics by altering historic vegetation composition and suppressing herbaceous productivity. Abundant woody plants often suppress native plants sufficiently to establish successional thresholds difficult to reverse without species augmentation. Juniper (Juniperus virginiana L.) is expanding in North American tallgrass prairie, but it is currently unknown if encroachment creates successional restrictions that limit restoration potential. We selected 16 50×50-m sites with juniper canopy cover ranging from zero to approximately 75% in tallgrass prairie near Stillwater, Oklahoma, USA. Juniper trees were removed from 7 of the sites along the gradient of juniper canopy cover. Canopy cover of plant species and herbaceous plant productivity were estimated at each site 1 year before and 1, 2, and 5 years after tree removal. Before trees were removed, plant species richness and productivity declined as juniper canopy cover increased, and plant community composition dissimilarity of reference sites increased as juniper canopy cover increased. These relationships remained consistent on all non-removal sites throughout the study. The first year after juniper removal, species richness increased on all removal sites compared to intact sites and productivity on removal sites increased two years after removal. Plant community dissimilarity between reference sites and juniper removal sites remained relatively high (30-60%) the first two years after tree removal on all removal sites, but dissimilarity was about 22% 5 years after juniper removal. Within 5 years, removal sites were comparable to reference plant communities. Grassland restoration frequently requires species manipulation and additional seeding, particularly when overcoming successional limitations. Juniper encroachment into tallgrass prairie alters plant community species composition and productivity. However, in our study, juniper associated succession limitations were not apparent, and complete autogenic restoration was achieved within 5 years without seeding or species manipulation. © 2014 The Society for Range Management.
Seasonal resource selection and distributional response by elk to development of a natural gas fieldGlobal energy demand is predicted to increase dramatically, suggesting the need to understand the role of disturbance from energy development better and to develop more efficient conservation strategies for affected wildlife populations. We evaluated elk (Cervus elaphus) response to disturbance associated with natural gas development in summer and winter, including shifts in resource selection and concomitant distribution. We collected elk locations prior to (1992-1995) and during (2008-2010) coal bed natural gas (CBNG) development in the ~ 498-km2 Fortification Creek Area (FCA) of northeastern Wyoming, USA, where approximately 700 CBNG wells and 542 km of collector, local, and resource roads were developed from 2000 through 2010. We developed resource selection functions for summer and winter using coordinate data from VHF-collared female elk prior to CBNG development and similar location data from GPS-collared female elk during CBNG development to assess spatial selection shifts. By pooling across all locations we created population level models for each time period (e.g., pre- and during development) and incorporated individual variation through bootstrapping standard errors for parameter estimates. Comparison of elk resource selection prior to and during natural gas development demonstrated behavioral and distributional shifts whereby during development, elk demonstrated a higher propensity to use distance and escape cover to minimize exposure to roads. Specifically, during-development elk selected areas with greater Rocky Mountain juniper (Juniperus scopulorum Sarg.) cover, increased terrain ruggedness, and farther from CBNG roads than prior to development. Elk distributional changes resulting from avoidance behavior led to a loss of high-use areas by 43.1% and 50.2% in summer and winter, respectively. We suggest reducing traffic, protecting woody escape cover, and maintaining refugia within the energy-development footprint to promote persistence of elk within energy fields. © 2014 The Society for Range Management.