Altered Rangeland Ecosystems in the Interior Columbia Basin

A workshop was held to address specific questions related to altered rangeland ecosystems within the Interior Columbia basin (hereafter referred to as the basin). Focus was primarily on lands administered by the Forest Service (FS) and Bureau of Land Management (BLM). Altered ecosystems were considered to be those where humaninduced or natural disturbances are of sufficient magnitude to change ecosystem processes. Long-term loss or displacement of native community types and reduction of productive potential makes it difficult or impossible to restore these ecosystems to historical conditions. Seventeen rangeland potential vegetation types (PVTs) that are found within the basin are briefly described. Descriptions of riparian or woodland vegetation are not included.

The major factors that have altered the 17 rangeland PVTs are discussed. The most common factors that have affected the PVTs found in the basin include livestock grazing, invasive species, and changes in fire regime. Climatic change has probably been an important factor, but it is difficult to identify the specific influences. Agricultural development has been an important factor on private lands, and in some cases, these influences have spread to adjacent BLM- and FS-managed lands.

Six rangeland PVTs were identified as the most seriously affected in the basin. Selection of these PVTs was related to the degree of alteration, areal extent of the PVT, and the overall importance to the basin as a whole. These include salt desert shrub, Wyoming big sagebrushâ€"warm, basin big sagebrush, mountain big sagebrushâ€"mesic west, mountain big sagebrushâ€"mesic west with juniper, and wheatgrass grassland.

Many altered ecosystems may be restorable, but success of these efforts is variable and untested for many restoration methods. Options exist to restore some altered rangeland ecosystems by restoring native plant communities, stabilizing ecosystem processes, reducing the spread of invasive species, or conserving existing biota. In some altered conditions, these options have a relatively high probability of success over the short term with low to moderate cost at the site scale. However, in other altered conditions, restoration options are expensive, have a low probability of success, and require long timeframes. Failure to restore the most severely altered PVTs will affect the future stability of these areas.

The PVTs differed considerably in the extent to which vegetation composition had changed. The feasibility of restoration of the six most severely altered PVTs in the basin was discussed by the workshop participants from four perspectives. The overall feasibility of restoration of the mountain big sagebrushâ€"mesic west was high. Restoration could primarily be accomplished through changes in the management of fire and livestock grazing. Potential recruitment of native species was high where seed sources were present and alteration by invasive species was low. These management changes could be enacted relatively inexpensively, and the vegetation would respond rapidly to the changes. Restoration of salt desert shrub and wheatgrass grassland PVTs was thought to be the least feasible. Restoration of these PVTs would in most cases require control of invasive species and seeding of native species. In addition, soil and topographic features limit many types of restoration practices. Recruitment rates of native species are low owing to severe environmental conditions such as low rainfall. Consequently, restoration would require a long time. Altered portions of the salt desert shrub are often dominated by annual grasses that greatly increase wildfire occurrence. Wildfires would need to be suppressed for many years to enable recruitment of the native shrubs in this PVT.

Restoration of those sites within the mountain big sagebrushâ€"mesic west with juniper in the early stages of woodland development was highly feasible. The response would be similar to that of the mountain big sagebrushâ€"mesic west. However, restoration of those sites that had advanced through succession to later woodland stages was less feasible. Juniper may have to be removed by using methods other than fire, such as cutting or other mechanical means. In many cases shrub and herbaceous species have been severely reduced on these sites. Shrubs and native perennial grasses have been successfully established through seeding, but little is known about the establishment of many of the native forbs associated with this PVT.

Altered sites in the Wyoming big sagebrushâ€"warm and basin big sagebrush PVTs have a moderate restoration feasibility because of the presence of invasive species and subsequent reduction of recruitment of species native to these PVTs. Many areas are also subject to frequent wildfire that prevents sagebrush recruitment. Severely altered sites require seeding of native species. Availability of seed sources is limited, and the establishment requirements for seedlings for many of these species is not well understood.

Greater sage grouse (Centrocercus urophasianus) and Columbian sharp-tailed grouse (Tympanuchus phasianellus) are extremely important species within the basin because of their widespread historical distribution, declining status, and potential use of most of the PVTs. Sage grouse densities vary by season and PVT because of seasonal movements and their dependence on sagebrush leaves during winter, shrub and herbaceous cover during spring, and forbs during summer. This natural variation has been exacerbated by differences in quantity, quality, and configuration of the PVTs. Of the six PVTs evaluated by workshop participants, only Wyoming big sagebrushâ€"warm, basin big sagebrush, mountain big sagebrushâ€"mesic west, and mountain big sagebrushâ€"mesic west with juniper were considered to be primary habitats for greater sage grouse. The mountain big sagebrush PVTs were believed to be relatively intact, thus offering the best opportunities for restoration. Unfortunately, these PVTs tend to be at relatively high elevations and somewhat isolated by vast areas of alternate habitats less suitable for sage grouse. The Wyoming and basin big sagebrush PVTs were believed to offer the greatest restoration challenge because of their dramatically altered characteristics. Nevertheless, their restoration may be the best way to realistically ensure the viability of greater sage grouse in the region, because of their immense size and the connections they provide between the smaller and more isolated PVTs. It is clear from this workshop that habitat management and restoration for greater sage grouse will require planning and action over a vast landscape.

Similar to densities of greater sage grouse, densities of Columbian sharp-tailed grouse also vary by season and PVT. Sharp-tailed grouse tend to depend on herbaceous cover during spring, forbs during summer, and deciduous shrubs and trees during winter. Of the six PVTs evaluated by workshop participants, only mountain big sagebrushâ€"mesic west, mountain big sagebrushâ€"mesic west with juniper, and wheatgrass grassland are likely to be primary habitats for sharp-tailed grouse. Although other PVTs also can be used by sharp-tailed grouse, their usage is often dependent on their proximity to a primary PVT. The mountain big sagebrush PVTs seem to be relatively intact, thus offering excellent opportunities for restoration. In contrast, the wheatgrass grassland has largely been eliminated by conversion to cropland. Among all 17 PVTs in the basin, the relatively high-elevation PVTs appear to be the most important for sharp-tailed grouse. These include Wyoming big sagebrushâ€"cool, threetip sagebrush, mountain big sagebrush (four types), wheatgrass grassland, mountain shrub, and fescue grassland (two types). Because many of these habitats are small, isolated, and long distances from existing populations of sharp-tailed grouse, it is likely that restoration should be focused in specific areas where there are opportunities to expand or connect existing populations. As with greater sage grouse, management and restoration of Columbian sharp-tailed grouse will require planning and action over a vast landscape.