TOPIC 6 The Eastern Range: Science
This section explores the science behind the threats impacting the eastern range. Scroll down the page to read each sub-section, or click the Science drop-down navigation to go directly to a sub-section.
Introduction
Two different types of threats impact sagebrush ecosystems and sage-grouse in the eastern portion of the range (Chambers et al. 2016):
- Persistent ecosystem threats: invasion of nonnative invasive plants, altered fire regimes, conifer expansion, and climate change. These are difficult to regulate and must be managed using ecologically-based approaches.
- Anthropogenic threats due to land uses and development: energy development, conversion to cropland, livestock grazing, mining, and urban, suburban, and exurban development. These can be regulated on public land, but because of human population growth and increasing resource demands will undoubtedly continue to result in degradation of sagebrush ecosystems. There is evidence that these factors lead to decreased ecosystem resilience, which is why fuels managers need to have some understanding of them.
Anthropogenic Threats
Described below some of the anthropogenic threats facing the eastern range.
Sublette County, Wyoming: Rural subdivision in Sublette County, Wyoming (photo by Thomas J. Christiansen). Chambers et al. (2016), Figure 14.
Figure 14: Click the image for a printable verison.
Of more critical concern is energy development, which is considered a persistent and widespread threat to almost all Greater Sage-Grouse populations in the eastern range. This includes oil and gas development (Chambers et al. 2016, Figure 17) and wind energy (Knick et al. 2011, Figure 12.17) among others. Among the potential side effects of energy development are removal of habitat, facilitation of invasive plant species, reduction of habitat quality through avoidance and other behavioral factors, facilitation of higher abundances of predators, and others.
Figure 12.17: Click the image for a printable verison.
Figure 17: Click the image for a printable verison.
In this video, Holly Copeland discusses some of the direct and indirect effects of energy development in Wyoming.
Cropland conversion is also a significantly greater risk in the eastern range, particularly in Management Zone I, due to generally higher precipitation and better soils than further west (Chambers et al. 2016, Figure 19; Smith et al. 2017, Figure 1). Cropland severely reduces habitat use by sage-grouse and very few leks persist in landscapes with > 15% cropland; 96% of active leks are found in landscapes with proportion cropland < 0.15 (Smith et al. 2016, Figure 2).
Figure 19: Click the image for a printable verison.
RESILIENCE AND RESISTANCE
Our ability to address persistent ecosystem and anthropogenic threats to sagebrush habitats can be greatly enhanced by understanding the effects of environmental conditions on resilience to stress and disturbance and resistance to invasion by nonnative plants. These concepts are more fully discussed in the Resilience and Resistance topic.
- Resilient ecosystems have the capacity to regain their fundamental structure, processes, and functioning when altered by stressors like invasive species, climatic factors such as drought and disturbances such as overgrazing by livestock and altered fire regimes. Species resilience is closely linked to ecosystem resilience and refers to the ability of a species to recover from stressors and disturbances.
- Resistant ecosystems have the capacity to retain their fundamental structure, processes, and functioning when exposed to stressors, disturbances, or invasive species. Resistance to invasion by nonnative plants is increasingly important in sagebrush ecosystems; it is a function of the abiotic and biotic attributes and ecological processes of an ecosystem that limit the population growth of an invading species.
The Greater Sage-Grouse is a broadly distributed and wide ranging species that can move long-distances between seasonal habitats and threat management necessarily requires a strategic, multi-scale approach that integrates both landscape prioritization and site-scale decision tools. Because of its widespread distribution and the broad range of sagebrush habitats sage-grouse use, managers have considered it as an umbrella species for identifying ecological conditions required for a larger set of sagebrush-obligate species across large landscapes. Holistic management approaches based on resilience science that address large-scale threats to sage-grouse habitat should benefit sagebrush ecosystems and most sagebrush obligate species.
Click the tab to learn about sage-grouse movement and dispersal.
Begin by listening to Shawn Espinosa describe sage-grouse movements.
Although Greater Sage-Grouse are generally considered to be a sedentary, non-migratory species, movements of individual birds have been documented and at least one population near the edge of its range is known to be migratory, with movements up to 120 km (74.6 mi) between the lek and the winter range (Tack et al. 2011). A recent analysis of sage-grouse movements using genetic markers confirms that relatively long-distance movements are a rare, but regular feature of sage-grouse biology between breeding seasons (Cross et al. 2017).
This important study documents that although most movements are within or outside of Priority Area for Conservation (PAC) boundaries, three of the 43 movements documented were among PACs (with a maximum distance moved of 69.8 km). An additional six movements were either from outside a PAC moving in or inside a PAC moving out; the maximum distance moved in these cases was an astounding 194.4 km.
Resilience of native ecosystems to stress and disturbance changes along climatic and topographic gradients at both landscape and local scales. At landscape scales, higher precipitation and cooler temperatures, along with greater soil development and plant productivity, typically result in greater resource availability and more favorable environmental conditions for plant growth and reproduction, which generally result in increased ecosystem resilience to disturbances and management treatments (Chambers et al. 2014). More resilient ecosystems typically exhibit smaller changes following perturbations and recover more rapidly than less resilient ecosystems. In contrast, lower precipitation and higher temperatures result in reduced resource availability for plant growth and reproduction and thus lower ecosystem productivity.
The key components of identifying and mapping resilience and resistance in order to better determine management strategies are discussed in the following section.
SOIL TEMPERATURE AND MOISTURE REGIMES
Soil climate regimes (temperature and moisture) integrate several different climate variables including mean annual temperature, precipitation, and seasonality of precipitation, thus providing a means of assessing climatic differences among ecoregions and effects on vegetation. These regimes can be mapped at appropriate scales to provide an extremely useful tool to help determine the appropriate vegetation treatments and the potential of success of such treatments. A map showing each soil temperature and moisture regime in the eastern range in one of three simplified categories of Resistance and Resilience (high, moderate, or low) is shown here (Chambers et al. 2016, Figure 28); see also Maestas et al. (2016).
SAGE-GROUSE BREEDING HABITAT MODEL
The breeding habitat model was developed to more accurately portray important breeding areas for the Greater Sage-Grouse (Doherty et al. 2016). The model uses sage-grouse 2010-2014 lek data as a proxy for landscapes important to breeding birds, because leks are central to the breeding ecology of sage-grouse and the majority of nests occur
within 4 miles of leks. The model evaluates characteristics such as vegetation, climate, landform, and disturbance variables around leks (within a radius of 4 miles) and provides an estimate of four levels of probability of occupied breeding habitat based on habitat characteristics for each sage-grouse Management Zone (Chambers et al. 2016, Figure 23).
