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Riversides and floodplains are some of the most dynamic areas of the landscape. During spring runoff, submerged floodplains provide critical feeding and spawning areas for fish and other aquatic species. In drier seasons, the water recedes to reveal a myriad of geomorphic features, each with its own characteristic flora and fauna. Fresh silt deposits, scoured riverbanks, sand bars, alluvial meadows, depression marshes, oxbow lakes, braided stream channels and lush floodplain forests interact to form a complex system rich in biodiversity.

In the Northern Appalachians, intact riparian corridors and floodplains are linear features, averaging about 200 acres with size varying between subregion (Figure 1). About 22, 000 intact, or semi intact, examples occur in the ecoregion, accounting for 3% (2.7 million acres) of the area. Most are found at low to mid elevations on sedimentary till, coarse sands or fine silt deposits.

Floodplain and Riverside Portfolio Summary

The screening criteria used to locate and identify the riparian systems most critical to maintaining biodiversity required that each qualifying example:

 Was large and contiguous: over 100 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, A or B quality ranks in US)

 Contained other confirmed biodiversity features (verification by element occurrences)

Size criteria were determined by an analysis of almost two thousand survey records for species and communities occurring on floodplain and riverside settings. Interestingly, size was not related to the likelihood of finding associated species as with other patch forming communities (e.g. summits, basin wetlands, etc.) probably because of the linear shape of riparian features. However, high quality examples, ranked A or B in the inventory data, of riparian communities were associated with modeled occurrences over 100 acres in size. None of the modeled occurrences under 100 acres had A-ranked communities in them.

Results

Floodplains are a large patch, linear ecosystem. Our goal was to identify a minimum of 10 exemplary examples per each of 29 bedrock/elevation combination. This totals to 290 occurrences distributed across the ecoregion. After examining the distribution of larger (>100 acre) floodplains occurrences we redistributed the 10-per-type numeric goal across the geology/elevation gradients in proportion with the number of possible occurrences acres (Table 3).

In all we identified 240 critical occurrences, 55 less than we needed to meet our total goal. We were slightly below our goals for most bedrock/elevation combinations with the highest deficiencies being in low elevation (20-800) coarse sediment environs where most of the floodplain forests occur (Table 3). Most of the deficient environments had candidate occurrence to evaluate and new critical one may come from that pool.