The High Divide A Landscape Perspective

Defining the High Divide The High Divide has existed conceptually since the 1990’s and is recognized as the region that straddles the continental divide, extending into both Idaho and Montana, connecting the Yellowstone Ecosystem to the Salmon-Selway Ecosystem. However, in order to develop a landscape-scale vision for the region that can provide the framework for local, site-specific conservation efforts, it is first necessary to develop a geographically explicit definition of the High Divide. Delineating a boundary for the High Divide should have an ecological basis that takes into account the uniqueness of the area when placed in the broader context of the Northern Rockies, while also encompassing the common landscape features that make the High Divide a discrete region. The connectivity of aquatic systems on both sides of the continental divide is also an important component in defining the region. Taking into account these two features, distinctive landscape characteristics and aquatic connectivity, a boundary for the High Divide was defined based on ecoregions and hydrologic units. Ecoregions are large areas that contain a unique assemblage of plant and animal species. While there is often considerable variability within an ecoregion, the broader landscape patterns of soils, terrain, and natural communities are repeated. Boundaries for ecoregions have gone through numerous iterations since the concept first emerged. For the purposes of this analysis, the Level III ecoregions published in 2002 for Idaho and Montana by the Environmental Protection Agency in conjunction with state agencies, the Forest Service, Bureau of Land Management, Natural Resources Conservation Serivce and US Geological Service are used. The Middle Rockies ecoregion incorporates the area that has generally been associated with the High Divide. In Idaho it borders the Snake River Plain ecoregion to the south and the Idaho Batholith to the west. In Montana it extends north to the confluence of the Clark Fork and Bitterroot Rivers where it abuts the Northern Rockies ecoregion and it extends east to the Missouri River. The Middle Rockies ecoregion is transitional between the moist Northern Rockies and the arid Snake River Plain. It is characterized by high mountains, covered with conifer forest, primarily lodgepole pine with wide dry valleys between mountain ranges. Beginning with the Middle Rockies ecoregion, the High Divide boundary was delineated with the additional consideration of aquatic systems. In Idaho the upper Salmon River basin, above the confluence with the Middle Fork of the Salmon River, is included in its entirety, despite the fact that the headwaters extend into the Idaho Batholith. The southern boundary in Idaho follows the ecoregional boundary between the Middle Rockies and the Snake River Plain. To the north, the boundary follows the state border that is also the divide between the North Fork Salmon and Bitterroot Rivers. The

2

Bitterroot River subbasin was not included in the High Divide due to its presence in the Idaho Batholith ecoregion and, unlike the situation with the Salmon River, its inclusion is not necessary for the upstream connection of the aquatic system. The High Divide then continues to the northeast to encompass the Big Hole River subbasin in Montana as the northern extent. The Beaverhead and Ruby River subbasins were included in their entirety while the northern extents of the Madison and Gallatin were excluded due to the increasing level of anthropogenic impacts associated with Bozeman. Figure 1 shows the result of the boundary delineation. Figure 1: Delineating the High Divide

Landscape Characteristics The High Divide as described above, encompasses 13.6 million acres in Idaho and Montana. The topographic diversity of the High Divide is the predominant landscape feature that shapes the biological diversity associated with the region. Figure 2 shows the terrain features which range from wide, flat valleys to rugged mountain peaks. It is this juxtaposition of extremes that make the region a unique landscape. To the west and

3

northwest of the High Divide the broad valleys disappear, while to the south and northeast, the mountain ranges diminish. Elevation in the region spans from a low of 3,000 feet at the confluence of the Middle Fork and Main Salmon Rivers, to a high of 12,665 feet on top of Idaho’s Mount Borah in the Lost River Range with an average elevation of 7,050 across the entire area. This broad range in elevations is reflected in the diversity of vegetation communities found across the High Divide. The diversity of slopes also contributes to the vegetation diversity and wildlife occurrences for species such as antelope and mountain goats that have habitat requirements constrained by slope. The wide valleys preferred by antelope with slopes less than 5% encompass 21% of the area while the slopes greater than 50% preferred by mountain goats cover 9% of the land area. Overall, approximately one-half of the High Divide is less than 20% slope. Figure 2: Topographic Diversity

Consistent with the area’s topographic diversity, there is also a wide diversity in plant communities ranging from the low elevation sagebrush grasslands to the high elevation subalpine forests. Table 1 below provides the acreage summary of the dominant habitat groups and Figure 3 shows the distribution.

4

Table 1: Land Cover Group Summary

Land Cover Group

Land Area inAcres

Percent of High Divide

Grasslands 1,577,000 11.6% Sagebrush 4,409,000 32.3% Douglas Fir 1,430,000 10.7% Lodgepole Pine 1,326,000 9.6% Mixed Subalpine Forest 1,356,000 9.9% Mixed Whitebark Pine Forest 830,000 6.0% Barren Land 376,000 2.7% Riparian/Wetland 439,000 3.2% Agriculture 593,000 4.4%

Figure 3: Land Cover

5

Land Status Land status within the High Divide is dominated by federal ownership with private lands making up just 20%, primarily in the valleys. Nearly 32% or 4.3 million acres is a forest service roadless area with another 443,000 acres of wilderness. Table 2 provides the acreage totals for land ownership and Figure 4 shows the distribution. Table 2: Land Ownership

Land Ownership

Land Area inAcres

Percent of High Divide

Forest Service 6,984,000 51.2% Bureau of Land Management 2,889,000 21.2% National Park Service 96,400 0.7% Fish and Wildlife Service 40,000 0.3% Department of Energy 54,200 0.4% State 699,000 5.1% Private 2,806,000 20.6%

Figure 4: Land Ownership

6

Habitat Quality Habitat quality across the High Divide varies as a function of land status and accessibility with the lower elevations and gentler terrain having experienced a greater degree of land conversion and anthropogenic impacts than the mountainous terrain. The private lands have experienced direct conversion to agriculture and development while the public lands have been subject to resource use, primarily timber harvest and livestock grazing. The population of the region is low, with only 48,000 people living in the High Divide in 2000. However, the anthropogenic footprint extends far beyond the population centers. The most pervasive impact affecting all unprotected lands except the steepest mountains is the 27,000 miles of roads that cross the region. In addition to habitat fragmentation, roads are also indicative of the intensity of human use of the land and serve as pathways for invasive plant species and motorized access. The habitat suitability analysis is based on five elements listed below. The spatial distribution of each of these elements was analyzed independently and thresholds were established for normalizing each variable on a 0-1 scale in order to avoid skewing results due to small areas with very high or very low values. The normalized values for each variable were then combined into a single habitat suitability data layer.

• Road density; • Distance from highways; • Human population; • Converted land; • Patch size.

The presence of invasive species is an important indicator of habitat quality but unfortunately there is little spatial data available on the extent of the problem and thus it was not possible to include it as a specific element of this analysis. However, the greatest concentration of invasive species are typically associated with disturbed lands and human access so the first four habitat quality elements may also be considered as surrogates for invasive species. Accurate spatial data of roads is difficult to obtain given the often ambiguous definition of a road. Therefore, this data may contain local inaccuracies but it is indicative of the general pattern of roads, including unimproved roads on public lands, across the High Divide. Road densities ranged from 0 to a high of 15 miles/square mile. The threshold of 4.7 miles/square mile was used based on analyses of the Interior Columbia Basin Ecosystem Management Project which classified road densities above 4.7 as having a very high adverse impact on wildlife and aquatic systems. Therefore, all road densities above 4.7 in this analysis were assigned a value of 0 and densities below that level were normalized on a 0-1 scale. Figure 5 shows the road densities across the region. When reviewing these results it is important to keep in mind that the values are indicative of a one square mile area. Therefore, a given cell may not have a road running through it but because it is within that one square mile radius of a road it is assigned a value greater

7

than 0. Thus the edges of ‘roadless areas’ may actually be portrayed with road densities above 0 due to the presence of border roads. Figure 5: Road Density

Highways were addressed specifically beyond the road density analysis due to their increased effect on wildlife as barriers and through direct species mortality. A distance of two miles was used as a threshold such that all areas greater than two miles were assigned a value of 1 and the highway corridors were normalized down to 0 at the highway. Population per square mile was calculated based on census block data from the 2000 census. Given the growth that much of this region has experienced since 2000, the actual values are likely to underestimate the current population but they should still be representative of the relative spatial patterns of population concentrations. The area weighted mean for population density in the region is 71 people/square mile. This was used as the mid-point for normalizing such that areas with at least twice that density were assigned a value of 0 on the normalized scale. Figure 6 shows the population per square mile.

8

Figure 6: Population Density

Determination of converted land was based on the land cover data from the Idaho and Montana Gap analysis projects. Lands classified as agricultural, urban, or developed were identified as converted for the purposes of this analysis. In addition to the discrete classification of these lands, a moving window of one square mile was used to provide a relative ranking of non-converted lands based on their juxtaposition to converted areas. Patch size was also incorporated into the habitat suitability analysis in recognition of the importance of connected landscapes to wildlife. Patches were defined based on the road network and converted lands. Contiguous areas between roads and developed or agricultural lands were delineated as discrete patches and normalized based on relative size. The threshold for normalization was 100 square kilometers which is twice the size of the minimum area required for core grizzly bear reserves. Figure 7 shows the patches identified in the analysis by size.

9

Figure 7: Patch Size

The normalized values for these five variables were combined to produce a final habitat suitability map that was used as a screen for further analysis of species distributions. Figure 8 shows the spatial pattern of habitat suitability.

10

Figure 8: Habitat Suitability

Terrestrial Species Analysis Consistent with the High Divide’s topographic and vegetative diversity, the region also supports a diverse array of wildlife species. The purpose of this analysis is to identify the important areas for five key species with very different habitat requirements that are found within the High Divide. Specifically, this includes pronghorn antelope, elk, moose, mountain goats, and sage grouse. The results of previous work by the Craighead Environmental Research Institute on grizzly bears and aquatic integrity by Pacific Rivers Council and American Wildlands have also been included. The general approach taken for the analysis of each species began with the wildlife habitat models from the Idaho and Montana Gap analysis projects. The results of these models show the distribution of a given species based on known occurrences, the species’ range, land cover requirements, and elevation constraints. The model criteria were reviewed for each of the two states and if necessary were modified for purposes of consistency across the state borders. In some instances the resulting distributions were further refined to include additional habitat requirements. A floating window of one

11

square kilometer was applied to the distribution data layer for the identification of areas with the highest concentration of potential habitat. This processing step results in a more consolidated and realistic representation of habitat than the highly pixilated raw distribution layers. The final step is the integration of the distribution data with the habitat quality. Given the wide-ranging character of these species and the modeled nature of the spatial data, isolated habitat patches of less than 2,500 acres were excluded. Pronghon Antelope Figure 9 shows the results of the pronghorn antelope analysis. In addition to land cover requirements, pronghorn distribution was also dependent on slope with a threshold of 20% for the identification of habitat. Thus this species is typically associated with the wide valleys of the High Divide. There is approximately 4.9 million acres of potential pronghorn habitat within the High Divide with private lands making up nearly 40% followed by Bureau of Land Management lands that comprise 38% of the habitat. Figure 9: Pronghorn Antelope Distribution

12

Sage Grouse The primary land cover requirement for sage grouse is sagebrush. The flat grasslands preferred by antelope are not included as sage grouse habitat. Instead of a slope constraint, the sage grouse distribution model uses an elevation criteria of 2,550 meters which limits the habitat to the hillslopes coming up from the valley bottoms. Habitat suitability was modified for sage grouse, taking into account the presence of power lines and cell towers where predatory birds may perch. Sage grouse have approximately 4.9 million acres of potential habitat within the High Divide. However, unlike antelope, the BLM is the primary land owner with 48%, followed by private land at 23% and forest service with 20%. Figure 10: Sage Grouse Distribution

13

Elk Given the extensive modeled distribution of elk habitat, an emphasis was placed on winter range and calving areas. Data developed by the Rocky Mountain Elk Foundation was used to highlight winter range, crucial winter range, and calving areas. While nearly all of the High Divide is considered general elk habitat, there is just 3.5 million acres of winter range and calving areas. The forest service is the primary land owner of these important areas for elk, managing 45% of the winter and calving habitat. The BLM is responsible for 30% and another 17% is found on private lands. Figure 11: Elk Distribution

14

Moose In order to highlight critical areas for moose, the Gap distribution data was refined to incorporate a 500 meter zone around riparian areas and streams. Based on habitat descriptions for moose by the Fish and Wildlife Service, the buffer zones were further refined to include only dense, conifer dominated forests that are important to moose, particularly during the winter months. Snow depth is the greatest determinant of moose habitat in the winter but there was not any data available on average maximum snow depths across the region so it was not possible to include this as a factor in the analysis. Given the habitat requirement of conifer forest, it is not surprising that 88% of the 2.4 million acres identified as potential moose habitat are managed by the forest service with private lands comprising just under 6%. Figure 12: Moose Distribution

15

Mountain Goat Mountain goats represent the antithesis of antelope, occupying the ridge tops and steepest terrain of the High Divide. Their modeled distribution includes parameters for both slope (greater than 40%) and elevation (higher than 1,650 meters). In order to capture the alpine meadows used by mountain goats that were excluded due to the slope criteria, an additional refinement was made. According to information published by the Fish and Wildlife Service, mountain goats will use flat meadows if they are within 400 meters of escape habitat such as cliffs. Areas over 80% slope were identified based on the terrain model and all alpine meadows and montane parklands within 400 meters of these cliffs were then included as mountain goat habitat. Given the remote nature of mountain goat habitat, it is not surprising that nearly all (95%) of the 2.8 million acres of potential habitat is managed by the forest service. Figure 13: Mountain Goat Distribution

16

Grizzly Bear The Craighead Environmental Research Institute and others have done extensive work on habitat suitability and connectivity analysis for grizzly bears through-out the High Divide region. It is not the intent of this study to conduct any additional analysis on grizzly bear but simply to show the results of these studies within the context of the High Divide as defined in this assessment. The forest service is responsible for the management of 85% of the 1.9 million acres identified as core areas while the BLM manages just 6% and another 5% falls on private lands. Figure 14: Grizzly Bear

17

Aquatics Pacific Rivers Council working in conjunction with American Wildlands have applied their Aquatic Integrity Area model to subwatersheds in the High Divide. The analysis identifies the highest integrity subwatersheds based on relative comparisons of human impacts, fish stocking, the proportion of non-native fish, and the presence of sensitive fish species. The subwatersheds in the High Divide contain five native coldwater salmonids, three of which are protected under the Endangered Species Act, bull trout, summer steelhead, and summer Chinook. Westslope cutthroat and Yellowstone cutthroat are also found within the waters of the High Divide and are considered sensitive species. Private and federal land owners are all important to the continued status of these subwatersheds as high aquatic integrity areas. The forest service manages 48% of the 3.8 million acres identified, while private land owners incorporate 25% of the land area and the BLM oversees 18%. Figure 15: Aquatic Integrity Areas

18

Conclusion The High Divide provides important habitat for a variety of native terrestrial and aquatic species and it has the potential to provide corridors between the Yellowstone and Salmon-Selway ecosystems for wide ranging carnivores such as the grizzly bear. Although the region contains large patches of high quality habitat, there are challenges in connecting these areas. Highways, human population centers, and high road densities are impediments to the movement of species and need to be addressed in the development of a landscape vision for the region as well as through local, place based conservation efforts. This analysis has provided an overview of landscape characteristics of the High Divide and how these features influence the distribution of different wildlife species. Given the variety of habitats occupied by these species, it is important that a landscape-scale vision incorporate the high quality areas across the spectrum of habitat types. Local conservation efforts focused on single species without a broader context from which to work, may fail to meet the needs of other species equally important to the character and ecology of the High Divide. The ecological integrity of the High Divide will ultimately be sustained through local, place-based efforts that make a difference on the ground. However, given the landscape nature of many of the species that live in the High Divide, and the complex environmental processes that sustain them, the conservation projects happening on the ground must be consistent with a broader framework that addresses the inter-dependent biological and physical features of this unique area. Before putting the pieces of a puzzle together, it is helpful to know what the final image should look like.