© The Nature Conservancy View/Download: Please click on the link(s) below and you will be given the choice of opening or saving to disk. JPG Download (JPG, 921 KB, Created January 01, 1999)

Rocky crags, vertical cliffs, landslide scars, steep river bluffs and precipitous talus slopes contribute unmistakable character to the rugged landscapes of the region. Over 15,000 of these steep vertical features occur here, being concentrated in mountainous subregions but found across all elevation zones and bedrock types (Figure 1). Most steep slope features are small, averaging 27 acres, with 75% being less than 25 acres and accounting for 1% of the ecoregion in aggregate (Figure 2). At lower elevations steep slopes are associated with downcutting by rivers whereas at very high elevations, they intertwine with summits and hillcrests to form large complicated mountain features.

Compositional variation among the different community types correlate with recognizable bedrock-elevation combinations. Although the locally-defined community types do not conform precisely to physical factors, there was strong correspondence in the data between known community locations, steep slope features and the various bedrock types and elevation zones (Figure 3). To ensure that we located the best examples of steep slope ecosystems across the full spectrum of types we set a goal of locating 20 occurrences for each of 19 bedrock-elevation combination.

Steep Slope Portfolio of Critical Sites

The screening criteria used to locate and identify the steep slope features most critical to maintaining biodiversity required that each qualifying occurrence:

 Was large and contiguous: over 25 acres.

 Was in good landscape settings (Land Cover Index < 20).

 Was in good condition based on ground surveys and expert opinion (corroboration by at least one source).

 Contained other confirmed biodiversity features (verification by element occurrences).

The size criterion was intended to insure that examples selected for the portfolio contained all their inherent species diversity and ecosystem functions. We determined the size minimum by examining over 1000 ground inventory points representing 298 species found on or directly adjacent to a steep slope feature. Of the species found on steep slopes, 69% were found only on examples greater than 25 acres, suggesting that larger features were more likely to contain a full complement of associated species. Restricting the analysis to a more narrowly defined set - species with three or more occurrences found consistently on steep slopes - 46 species were found only on examples over 25 acres, and no species were restricted to small examples. Included in the former group were much of the alpine flora, long-tailed rock shrew, rock vole, bald eagle, smooth cliff fern, mistassinica primrose, scirpus-like sedge, White Mt. saxifrage and many others (Tables 2 and 3). On average 88 % of the occurrences for any given species were likely to be on a slope over 25 acres.

Our goal was to identify a minimum of 20 exemplary occurrences per 19 bedrock/elevation combinations totaling to a minimum goal of 380 total occurrences distributed across the ecoregion. After examining the distribution of larger (>25 acre) steep slope occurrences we redistributed the 20-per-type numeric goal across the geology/elevation gradients in proportion with the number of possible occurrences acres (Table 3).

We identified 829 critical occurrences, 449 more than we needed to meet our minimum goal. With one exception we met our goals for identifying sites within each bedrock/elevation combination as well and thus, the portfolio is generally sufficient with respect to steep slopes except on low moderately calcareous or mafic bedrock (Table 3).

Candidate and Supporting occurrences

In addition to the critical occurrences, this analysis encompassed a large number of less notable, or poorly surveyed steep slopes that did not meet our screening criteria for being a critical feature. We accounted for their potential contributions to biodiversity by sorting them into two categories and totaling the amounts of each.

 Candidate occurrence: A feature that met the criteria for size and landscape context but for which we had no verification or corroboration as to their condition and biodiversity contribution. Many of these may be added to the portfolio after ground verification and are a logical place to focus inventory efforts.

 Supporting occurrence: A feature that did not meet the criteria for size and landscape context but may play a supporting role in supplementing the critical sites.

Many of the candidate and supporting occurrences already occur on protected reserves and thus are part of the defacto conservation picture for the region. As protected examples may serve to bolster biodiversity protection we included them in some of our analyses for context. However, candidate and supporting occurrences were not counted as contributing to the portfolio goals.

The importance of recognizing the defacto examples was provided by the few, single-occurrence steep slope species that were known only from small occurrences (e.g. northern stick seed).

Of the half million acres of steep slopes in the ecoregion, this analysis identifies e portfolio highlights the 346 sites most critical for biodiversity conservation (10 percent by number or 27 percent by area). The key sites, are well distributed across bedrock and elevation gradients and are about 1/3 protected (3% by count /16%) by area. Conservation is needed mostly for low elevation slopes on calcareous and sedimentary features.