Title: Surveys and predicted distribution models for land mollusks on USFS Northern Region lands
Description: Using the NatureServe website and prior reports as a starting point, we compiled a list of 29 land snail taxa within the U.S. Forest Service Northern Region (Region 1) area that were globally ranked in 2005 as G1-G3 or T1-T3, thereby meeting USFS Species of Concern (SOC) criteria, and two additional G5 snail taxa state ranked S1-S2, thereby meeting USFS Species of Interest (SOI) criteria.  We also compiled a list of eight slug taxa ranked in 2005 as G1-G3, and three additional slug taxa ranked G4-G5 but S1-S2, again meeting the respective USFS criteria for SOC or SOI. Nineteen of these SOC/SOI species (11 snails, 8 slugs) have been documented in Montana as of 2007.  Montana Natural Heritage Program surveys in 2005 included lands in both Idaho and Montana, in 2006 they were restricted to Montana. This report presents results of the 2007 surveys, again restricted to Montana. Our objective was to gather additional distribution data to aid in the development of predictive distribution models and maps.  We conducted a total of 34 site surveys on National Forest units in Montana in 2007, primarily targeting areas where greatest diversity of SOC and SOI species could be expected but also where prior surveys were lacking; these were mostly (but not exclusively) west of the Continental Divide. SOC and/or SOI taxa were found at 19 (55.9%) of the sites. Site surveys were distributed on the Montana Forests as follows: Kootenai (16), Lewis & Clark (8), and Lolo (10).  We documented 38 locations for nine USFS Region 1 SOC taxa and two SOI taxa during our 2007 surveys: Alpine Mountainsnail Oreohelix alpine (1 site), Carinate Mountainsnail Oreohelix elrod (1 site), Humped Coin Polygyrella polygyrella (1 site), Fir Pinwheel Radiodiscus abietum (6 sites), Pale Jumping-slug Hemphillia camelus (4 sites), Marbled Jumping-slug Hemphillia danielsi (1 site), Magnum Mantleslug Magnipelta mycophaga (4 sites), Pygmy Slug Kootenaia burkei (9 sites), Smoky Taildropper Prophysaon humile (6 sites), Lyre Mantleslug Udosarx lyrata (1 site), and Sheathed Slug Zacoleus idahoensis (4 sites). Most locations were from west of the Continental Divide in mesic forest habitats (e.g., western redcedar, western hemlock, mesic Douglas-fir, grand fir), but locations for the two species of mountainsnail (Oreohelix) were exposed rocky terrain above treeline on the Scapegoat Plateau just east of the Continental Divide.  In 2007, we collected additional location data for two SOC slug species new in 2005 to the known mollusk fauna of Montana: Pale Jumping-slug and Pygmy Slug. The 2007 survey also added several new Montana locations for a third SOC slug species, Smoky Taildropper, which was documented in Montana only once prior to 2004. New State Rank adjustments are noted in this report as a result of the 2005-2007 surveys, the detection probability and site occupancy surveys conducted in 2006 and 2007, and the predicted distribution models produced in 2007. We collected distribution data in 2007 on 19 additional non-SOC/SOI species as we encountered them during our surveys.  Predicted distribution models were developed at 90m pixel resolution, using our point location data and 11 environmental data layers chosen for their assumed relationship to land snail requirements:  elevation, slope, curvature of land surface, annual precipitation, maximum July temperature, minimum January temperature (all continuous variables), aspect, geology, 1992 National Landcover Data, soil temperature class, and STATSGO soils (all categorical variables). Overall, the predicted distribution model output indicates the known ranges of a number of species may be extended by focusing future survey effort in the vicinity of Glacier National Park, the Seeley/Swan area, the South Fork of the Flathead River drainage, the Mission Mountains and the Bitterroot Mountains in Mineral County. Major gaps in survey effort on U.S. Forest Service lands still exist in a number of areas, but model output indicates the greatest number of gaps in known species ranges (especially Species of Concern) may be filled in with additional surveys focused on portions of northwestern Montana, the Bitterroot Mountains in Mineral and Ravalli Counties, Beaverhead, Madison, and Silver Bow Counties, and portions of the island mountain ranges in eastern Montana. In addition to these gaps, a summary of elevations on U.S. Forest Service lands in Montana and elevations of mollusk survey locations in 2005-2007 indicates high elevation sites have been under-sampled. We intend to fieldtest the predictive distribution models with surveys focused on these regions during the 2008 field season.
Subjects: Geographical distribution, Slugs (Mollusks), Mollusks, Snail populations, Habitat surveys
Places: Montana, Lolo National Forest (Mont.), Lolo National Forest, Kootenai National Forest (Mont. and Idaho), Lewis and Clark National Forest, Lewis and Clark National Forest (Mont.)