Title: Land mollusk surveys on USFS Northern Region lands
Description: Using published reports and the NatureServe web site as starting points, we compiled a list of 29 snail taxa within the U.S. Forest Service Northern Region (Region 1) area globally ranked in 2005 as G1G3 or T1T3, thereby meeting USFS Species of Concern (SOC) criteria, and two additional G5 snail taxa state ranked S1S2, thereby meeting USFS Species of Interest (SOI) criteria. We also compiled a list of eight slug taxa ranked in 2005 as G1G3, and three additional slug taxa ranked G4G5 but S1S2, again meeting the respective USFS criteria for SOC or SOI. Heritage Program surveys in 2005 included lands in both Idaho and Montana; the 2006 Heritage Program surveys were restricted to Forests in Montana.    We conducted a total of 156 site surveys across National Forest units in Montana in 2006, primarily targeting areas lacking prior surveys. SOC and/or SOI taxa were found at 49 (31.4%) of the sites.  Site surveys were distributed on the Montana Forests as follows: Beaverhead-Deerlodge (14), Bitterroot (18), Custer (36), Flathead (15), Gallatin (9), Helena (15), Kootenai (24), Lewis & Clark (8), and Lolo (17).    We documented 106 locations for eight USFS Region 1 SOC taxa and five SOI taxa during our 2006 surveys: Striate Disc Discus shimekii (2 sites), Berrys Mountainsnail Oreohelix strigosa berryi (1 site), Robust Lancetooth Haplotrema vancouverense (9 sites), Humped Coin Polygyrella polygyrella (5 sites), Fir Pinwheel Radiodiscus abietum (25 sites), Pale Jumping-slug Hemphillia camelus (2 sites), Marbled Jumping-slug Hemphillia danielsi (5 sites), Magnum Mantleslug Magnipelta mycophaga (4 sites), Pygmy Slug Kootenaia burkei (7 sites), Reticulate Taildropper Prophysaon andersoni (1 site), Smoky Taildropper Prophysaon humile (24 sites), Lyre Mantleslug Udosarx lyrata (2 sites), and Sheathed Slug Zacoleus idahoensis (20 sites). Most locations are from west of the Continental Divide in mesic forest habitats (e.g., western redcedar, western hemlock, mesic Douglas-fir, grand fir). Distribution maps showing locations for all terrestrial mollusk taxa can be viewed at the Montana Natural Heritage Program Tracker website http://mtnhp.org/Tracker.    In 2006, we collected additional location data for two SOC and one SOI slug species new in 2005 to the known mollusk fauna of Montana:  Pale Jumping-slug, Pygmy Slug, and Reticulate Taildropper. The 2006 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.  As a result of the 2005 surveys, Global Ranks shifted downward for five species (Humped Coin, Fir Pinwheel, Pale Jumping-slug, Pygmy Slug, and Smoky Taildropper). Additional Global and State Rank adjustments may be warranted following the results of the 2006 survey effort. We collected distribution data on 31 additional non-SOC/SOI species as we encountered them during our surveys, including one species, Boreal Top (Zoogenetes harpa), new to the known terrestrial mollusk fauna of the state.    At least some SOI G4G5 taxa found during our 2005-2006 surveys may prove to be distinct from related coastal populations, as their disjunct distributions are similar to some vertebrate amphibian taxa (e.g., Dicamptodon, Ascaphus, Plethodon) now split into coastal and Rocky Mountain sister species. Therefore, we think it desirable to conduct genetic analyses of several mollusk SOC and SOI taxa to determine it they represent forms meriting full species status.  Additional inventory is also desirable to fill remaining distribution gaps, describe habitat associations more thoroughly, and laying the foundation for development of a long-term monitoring scheme and standardized survey methodology.    Detection probabilities for terrestrial mollusks were evaluated with multiple surveys of individual sites on the Kootenai National Forest as a pilot project to: (1) compare naïve site occupancy rates with estimates adjusted for the fact that species are not detected at all sites where they are present; and (2) plan future inventory and monitoring efforts. Models best fitting the resulting data all indicated that detection probabilities were not significantly different between surveyors. For those species with sufficient data, estimated detection probabilities ranged from a low of 0.095 to a high of 0.886, and approximated a normal distribution with mean = 0.48, median = 0.49, and mode approximating 0.6. Robust estimates of site occupancy resulting from multiple surveys of individual sites were almost universally higher than naïve site occupancy rates from single visit surveys (mean = 0.11, median = 0.05, mode approximating 0.06, and range = 0.00 to 0.658 higher).    The detection probability analysis indicates evaluating the effects of imperfect detection of species can be extremely important in preventing the designation of a species of management concern when it lacks justification for this attention. In general, simulations showed that: (1) when site occupancy rates are truly below 0.8, detection probabilities need to approach 0.4 before acceptable confidence intervals result; (2) existing levels of sampling effort (approximately 50 days or 200 surveys) is adequate for monitoring most individual species when detection probabilities exceed 0.4, but is inadequate for at least a few Species of Concern, and may be generally inadequate for monitoring larger groups of species across larger regions.    Increasing detection probability can dramatically reduce the size of confidence intervals. Pilot studies examining the effects of survey covariates (such as weather, temperature, and spring vs. fall surveys) on detection probability may result in cost savings. In the future we recommend additional pilot surveys to evaluate baseline levels of site occupancy and detection probability for all terrestrial mollusk species in Montana not evaluated with this pilot effort. Systematic surveys also need to address how detection probabilities vary with survey covariates (such as weather, temperature, and season of survey) and site covariates (such as cover type, elevation, aspect, and timber harvest regime). This will provide a sound basis for making decisions about the status of species and evaluating the impacts of forest management practices.
Subjects: Surveys, Slugs (Mollusks), Snails, Mollusks
Places: Montana