The Sagebrush Cooperative

Management Issues: Fragmentation and Development

Natural resource managers and researchers have become increasingly aware of the negative consequences that fragmentation and development can have on sagebrush steppe landscapes. By themselves, development generally shrinks available habitat and fragmentation reduces the abundance of large, contiguous habitat patches. Perhaps as important, these processes frequently exacerbate other management challenges, such as providing additional vectors for exotic species or further disrupting natural fire regimes.

Historically, sagebrush-dominated vegetation was one of the most widespread habitats in the country. However, the majority of sagebrush ecosystems have been lost, fragmented or altered in some way by human activities (BLM 2004). Currently some intact, functioning sagebrush communities do exist but are interrupted or fragmented by structures, small disturbances, and transportation systems. These disturbances are generally linear or patchy when compared to larger areas of habitat loss caused by wildfires or urban development (BLM 2004). While large, spatially-extensive areas of lost habitat are easily identified as being a problem for sagebrush-dependent species such as sage-grouse, levels of acceptable habitat fragmentation are not as easily established for either spatial extent or local magnitude of the fragmenting action. The consequences of fragmentation to sage-grouse vary, but can include competition for fewer suitable nesting sites, reduced food supplies, the isolation of breeding habitat from brood-rearing areas and leks from nesting habitat (BLM 2004). Such outcomes may lead to lower reproduction rates for sage-grouse and other wildlife species that use this habitat for all or part of their life cycle. At this time there are no minimum or optimum sizes of contiguous sagebrush landscapes known to be “best” for sage-grouse and other sagebrush associated species. It is assumed that larger unfragmented landscapes are more desirable than small isolated patches (BLM 2004).

Residential development

The human population in western sage steppe habitat is growing rapidly. In the Columbia Plateau, remnant shrub-steppe habitats are subject to conversion to agriculture to feed this population increase. In the Blue Mountains and East Cascades ecoregions, rapidly growing human populations near Bend, Redmond and Madras, and slowly but steadily growing populations near Baker City and La Grande are resulting in land use conversion, habitat loss, and habitat fragmentation (ODFW 2006). People living in cities require resources to sustain their lives. Those resources either need to come from the surrounding region or must be transported into the cities from elsewhere. Development in the wildland/ urban interface and construction of infrastructure to support burgeoning populations (energy developments like coal-fired power plants and transmission corridors, water extraction or diversion, and pipelines) displaces sage steppe-associated wildlife species (Chambers 2008). Issuances of rights-of-way and increases in technological capabilities have reduced the limitations on moving resources and have increased human connectivity, while decreasing habitat connectivity. In addition, increased affluence has resulted in additional uses of lands surrounding cities for development of homes on larger acreages or for motorized recreation using all-terrain vehicles, motorcycles, or 4-wheel drive vehicles. (Connelly et al. 2004).

Agricultural conversion

Widespread agricultural conversion of sagebrush habitat was initiated by the United States government under the Homestead Act of 1862 and Desert Lands Entry Act of 1877. Lands first converted to agriculture were concentrated in those regions having deep, fertile soils and water for irrigation (Scott et al. 2001). These prime areas for growing crops were claimed early during settlement. For example, almost the entire basin big sagebrush habitat of the Idaho Snake River Plains has been converted to cropland and in Washington, agriculture has replaced 75% of the shrub steppe in deep soils (Hironaka et al. 1983). An estimated 10% of total sagebrush steppe habitat has been converted to agriculture; irrigation is not feasible or the topography and soils are limiting on the remaining 90% (West 1996). However, future conversions are still a threat because technological increases in irrigation methods now permit agricultural development on steeper terrains and in regions further from river floodplains.

Although sage-grouse are known to forage on agricultural crops, such as alfalfa (Patterson 1952), extensive cultivation and fragmentation of native habitats have been associated with sage-grouse population declines (Schroeder 1997; Braun 1998; Leonard et al. 2000; Aldridge and Brigham 2003). Avoidance of agricultural landscapes and the strong association with sagebrush habitat reinforce the obligate dependence of native shrub-steppe habitats for sage-grouse populations. Agricultural development indirectly influences wildlife in sagebrush habitats by providing access for predators such as domestic cats and red fox (Vulpes vulpes) as well as to corvids and parasitic cowbirds (Molothrus ater) (Vander Haegen and Walker 1999, Vander Haegen et al. 2002). Irrigation and chemicals applied to crops also can influence sage-grouse and other wildlife that are attracted to these ecological traps. Irrigation channels fragment habitat and application of organophosphate insecticides has been found to cause mortality to sage-grouse foraging in treated alfalfa and potato fields (Blus et al. 1989).

Some habitat loss to agriculture may have been mitigated through conversion of cultivated lands to Conservation Reserve Program (CRP) perennial cover over the last few decades. Connelly et al. (2004) noted that land enrolled in CRP markedly increased from 1987 to 2004 and a study in Washington found that the proportion of nests in CRP lands significantly increased from 31% in 1992–1994 to 50% in 1995–1997 (Schroeder and Vander Haegen 2010). The increase appeared to be associated with maturation of CRP fields, which were characterized by increased cover of perennial grass and big sagebrush (Artemisia tridentata). A reversal of population decline in north-central Washington demonstrated that these CRP lands may have a positive effect on sage-grouse populations. (Schroeder and Vander Haegen 2010).

Maintaining connectivity

There are many conservation and restoration measures that can be undertaken to help maintain the connectivity of sage steppe habitats and mitigate the aforementioned issues associated with development and habitat conversion. The following is a partial list of possible actions (BLM 2004):

• Encourage placement of new utility developments (power lines, pipelines, etc.) and transportation routes in existing utility or transportation corridors to minimize fragmentation of sage-grouse habitat.
• Place new roads where construction activity and use is concentrated and does not impact critical areas such as leks, nesting, brood-rearing, winter habitat, and riparian areas.
• Manage existing road use to decrease the level of disturbance during critical periods such as sage-grouse breeding (lek use) by implementing seasonal or daily use schedules, by limiting traffic volume, and/or by posting speed limits.
• Install anti-perching devices on existing or new power lines in occupied sage-grouse habitat, or habitat identified for restoration, to minimize raptor use of these poles.
• Locate new structures associated with recreation (picnic areas, campgrounds, wildlife viewing sites, dispersed recreation sites, kiosks and parking lots) and livestock management facilities (corrals, water pipelines and tanks/troughs, exclosures, etc.) away from crucial breeding, brood-rearing and winter habitat; or manage disturbance with seasonal or daily timing restrictions.
• Design and locate the placement of fences for livestock, wildlife, wild horse and burro, recreation and develop site protection so as not to disturb important sage-grouse habitat areas.
• Manage dispersed recreation activities such as hiking, mountain biking, and horseback riding to minimize impacts to vegetation and sage-grouse in sensitive sage-grouse habitat areas. Keeping these users on established trails will minimize impacts to sage-grouse habitat and activities.
• Consider seasonal closures to protect priority sage-grouse habitat if other alternatives will not achieve desired objectives.