Assessments

* Natural Diversity Database

* Terrestrial Vertebrates Restricted to the Sierra Nevada

MANAGEMENT STRATEGY

* SNEP Significant Areas Inventory

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1. What is the minimum area required to represent all Sierran plant community types in BMAs? How does a representative BMA system compare to the existing set of parks, wilderness areas, and reserves in the region?

If one ignores current land ownership and management designations and sets out to represent plant communities proportionately in a BMA system based on watersheds whose average size is 7,500 acres, an efficient BMA system requires land in direct proportion to the target level, at least over the range of target levels examined in this study. In other words, it takes roughly 10% of the region to meet a 10% goal, and 25% of the region to meet a 25% goal. The pattern of selected watersheds is very different from the current distribution of parks and wilderness areas, which are concentrated at middle and high elevations in the central and southern portion of the range.
In the northern Sierra, if one starts with a BMA system composed of Class 1 lands as defined by the Gap Analysis Project (see Ownership and Management of Sierran Plant Communities earlier in this chapter), only five of fifty-nine plant community types exceed a 10% target level. At a minimum, a representative BMA system to meet this target level would require roughly 500,000 acres to include all plant community types. This is an area roughly two-thirds the size of Yosemite National Park.
In the central and southern Sierra, Yosemite, Sequoia, and Kings Canyon National Parks, despite their large size, do not encompass the full suite of plant community types. Roughly half of the native plant community types in these regions do not meet or exceed a 10% target. Meeting that target would require a minimum of roughly 370,000 acres of additional BMA land, 30% of which is currently privately owned.
Increasing the size of the BMA units by a factor of three, from planning watersheds to superplanning watersheds (approximately 22,500 acres) has a surprisingly large effect on the distribution and areal efficiency of the solution, increasing the area required to reach a 10% target by 27%. This illustrates both the sensitivity of the model results to the choice of planning sites and the trade-off between increased BMA size and decreased efficiency for representing regionally dispersed elements of biodiversity. However, the preservation of many elements of biodiversity (such as large animals) and processes (such as fire) requires units at least as large as superplanning watersheds.

2. How does the location of BMAs relate to the distribution of areas of special interest that have been identified in other SNEP assessments and scenarios?

Solutions using the BMA model show only a modest degree of overlap with other SNEP biodiversity strategies, unless the model weighting factors are adjusted to favor those areas (e.g., Aquatic Diversity Management Areas and Areas of Late Successional Emphasis). Overlap is slight because the latter designations are predominantly located on public lands, whereas many plant communities can be adequately represented only if private lands are included in the solution. However, BMAs can be selected that not only aim to preserve biodiveristy but also favor other SNEP areas of emphasis, especially in the northern region.

3. Can a representative BMA system be established on public lands only? If not, what area of private lands is required? How does the area requirement change if lands that are currently administratively withdrawn from grazing and timber harvest are classified as BMA lands?

Public lands alone are insufficient to create a BMA system that adequately represents all plant community types of the Sierra Nevada, even if administratively withdrawn lands are included in the solution. Many of the foothill plant community types occur almost exclusively on private lands.

4. How sensitive is the siting of BMAs to the way in which biodiversity is measured? Specifically, how do solutions designed to represent plant community types compare to solutions designed to represent vertebrate species?

Terrestrial vertebrates are reasonably well represented in a BMA system selected for plant communities. A BMA system selected for vertebrates alone, however, has little overlap with the one for plant communities. Although the two types of solutions were comparable in the area required, there were considerable differences in the sites selected as optimal for representing vertebrates versus those for representing plant communities. Because BMAs are based on watersheds and thus implicitly include stream systems and their adjacent riparian zones, they can be designed to provide for the large proportion of wildlife dependent upon riparian habitats; their weakness in this regard is that no account is taken of upstream conditions and their potential impacts on the BMA watershed, unless explicit measures are included to consider those factors.

5. Do some areas emerge from the analysis that appear especially well suited to serve as BMAs?

Although the modeling exercise has real limitations, certain geographic areas were consistently identified in the alternatives as well suited to become BMAs, based on the biological, efficiency, and suitability criteria, and these areas therefore were less sensitive to changes in model assumptions and objectives. In the northern region, these general areas include the lower elevations in Calaveras County and portions of the Cosumnes River basin, the middle elevations of Sierra County north of Highway 49, and parts of Plumas County east of Highway 89 and south of Highway 70. Frequently selected watersheds in the central region are scattered along Highway 49, particularly in Mariposa County. Few watersheds are needed from higher-elevation zones because Yosemite National Park provides coverage for most conifer and subalpine community types. Likewise in the southern region, higher-elevation communities are generally well represented in the national parks. The areas of BMAs from the alternatives for this region tend to concentrate along the South Fork of the Kern River to Walker Pass and along the Greenhorn Mountains.

Implications

The criteria for evaluating different model alternatives were simply the area required and the total suitability of the selected watersheds. The solutions are sensitive to the size of the planning region and of the planning units (watersheds), the weights used to assign suitability, the starting BMA system, and the measures of biodiversity. The model was designed to produce solutions with minimum area and maximum suitability. However, the solutions may not be optimal with respect to other design criteriafor example, social desirability, political feasibility, economic cost, spatial arrangement of the sites to provide connected biological (especially vertebrate) habitat, or future changes in the distribution of habitats and suitability factors. The model weighting factors can be adjusted to favor certain goals, such as upstream aquatic conservation or connected riparian systems. Again, we emphasize that the purpose of the modeling was to explore possible dimensions of plausible BMA systems, rather than to identify the specific set of sites that would best meet the stated goals.