The Effects of Ski Resorts in the Lake Tahoe Region of California on Population Dynamics of the American Marten

The Effect of Ski Resorts on Population Dynamics of the Pacific Marten in the Lake Tahoe Region of California and Nevada, 2009 - 2011 Final Report 16 September 2013 Keith M. Slauson and William J. Zielinski, Principal Investigators USDA Forest Service, Pacific Southwest Research Station, Redwood Sciences Laboratory, 1700 Bayview Dr., Arcata, CA 95521 USA Southern Nevada Land Management Act Project #: P022 Project Collaborators: Lake Tahoe Basin Management Unit El Dorado National Forest Tahoe Region Planning Agency Heavenly Ski Resort Homewood Mountain Resort Sierra-At-Tahoe Resort Wildlife Genetics Laboratory, Rocky Mountain Research Station, U. S. Forest Service 1 Executive Summary From 2009-2011 we investigated the effects of developed ski areas on the distribution and population dynamics of Pacific martens (Martes caurina) in the Lake Tahoe region of California and Nevada. Our study design included the comparison of 3 ski areas with 3 paired control study areas. Using hair snares (winter) and live traps (summer) we systematically identified or captured martens at each study area to determine the occupancy and demographic characteristics. Over 3.5 years, including the 1-winter and 3 spring-summer capture seasons, a total of 96 (66M:33F) martens were included in the study. The development of the 3 ski areas involved the conversion of 30-34% of forest habitat to largely non-forest habitat. Remnant forest habitat within ski operations areas was fragmented into 65-100 patches, with >85% of all patches <10 hectares in size. Marten movement was strongly affected by the width of individual ski runs and by the cumulative width of runs that had to be crossed to move between capture stations. Martens typically did not cross individual ski runs that exceeded 20 m or combinations of runs that exceeded 30 m in cumulative crossing width. Female martens used smaller average ski run crossings, <15 m, than males. Adult males positioned their use areas to minimize the inclusion of ski runs and habitat within the ski operations areas. During winter, marten occupancy was significantly reduced within ski area operations boundaries. Martens occupied 52% of stations in operations areas compared to 88% outside operations areas. Station visitation rates were also significantly reduced in operations areas compared to outside them, suggesting that martens made less frequent use of habitat in operations areas during the winter. The amount of habitat affected during the winter, due to avoidance or reduced use, represented 15-37% of the total ski area study areas. During the spring-summer season marten occupancy was not significantly different between ski areas and controls or inside or outside the operations areas. This suggest that ski area impacts are greatest during the winter season and the combination of habitat alteration and winter recreation activities are the cause for the winter impact on marten occupancy. Although spring-summer occupancy did not differ between ski areas and controls, the processes underlying the changes in occupancy from winter to spring- summer differed. In controls, residents contracted the space they used and dispersers that were present in winter left the area by summer. In ski operations areas, occupancy declined from winter to spring similarly outside operations areas as residents contracted their space use but increased from winter to spring inside operations areas due in large part to the arrival of new individual martens. 2 We did not find significant effects of ski areas on estimates of population density during spring-summer, female survival, reproduction, or age structure. The primary effects on martens were season- and sex-specific. Winter ski recreation activities significantly affect marten habitat use within ski operations areas. However, this affect is mediated somewhat by females seasonal avoidance of habitat located in ski operations areas during winter recreation activities. Adult males avoided using habitat within ski operations areas year-round. A number of indicators of habitat use by males demonstrated negative effects on survival of males. Our results suggest that martens and ski areas can coexist if habitat across ski areas is connected, seasonal impacts are limited to avoid the denning and kit rearing season (March-August), and reproductive habitat is maintained and enhanced. 3 1.0 Introduction High-elevation conifer forests of the Sierra Nevada have historically provided some refuge from human impacts including trapping and timber harvest, but these forests have increasingly become focal areas for winter recreation. Because American martens (Martes caurina) are active year-round and are most energetically stressed during winter, winter recreation has the potential to have significant negative impacts. The two types of winter recreation most likely to negatively affect martens are snowmobiling and creation and operation of ski resorts. There have been very few studies on the effects of these types of recreation on martens. However, a recent study in the Sierra Nevada found that managed snowmobile use did not affect marten occupancy or activity patterns and that this recreational activity largely occurred during the daytime, when martens are not typically active during the winter (Zielinski et al. 2008). In comparison to snowmobile recreation, developed ski resorts have the potential to have more permanent and concentrated effects on martens and their habitat. Ski resort development includes forest habitat alteration in the form of habitat loss and fragmentation of remnant forest to create ski runs, roads, and resort infrastructure. Furthermore, during the ski recreation season, high densities of ski recreationists are present and distributed across resorts. There are approximately 25 ski resorts in the Sierra Nevada, nearly all occur within the range of the marten. The Lake Tahoe region includes about half of these resorts, constituting the highest density of resorts in the Sierra Nevada and one of the highest in North America. Martens typically avoid open areas lacking overhead cover or tree boles that provide vertical escape routes from predators (Drew 1995) and select foraging routes to avoid entering open areas in favor of remaining in areas with forest cover (Cushman et al. 2011). Martens have been shown to avoid areas when 25-30% of mature forest is removed (Bissonette et al. 1997, Potvin et al. 2000), favoring areas composed of higher proportions of high quality habitat providing the necessary prey resources, complex physical structure near the ground surface to increase prey vulnerability to capture (Andruskiw et al. 2009), and resting locations in large diameter live and dead woody structures (Thompson et al. 2012), conditions typically most abundant in mature and old growth forests. Thus, by the nature of their development ski resorts force martens to cross openings in order to use habitat within their operational footprints. However, on many ski resorts in California and Nevada, remnant forest patches are left relatively intact, potentially providing suitable habitat between run crossings. In addition to habitat alteration, activities during the winter recreation season have the potential to negatively affect martens. Snow compaction from grooming activities alters surface consistency making it easier for larger-bodied carnivores (e.g., coyotes [Canis 4 latrans]) which, unlike martens are not adapted for deep, soft snow, to expand their winter ranges (Bunnell et al. 2006, Whiteman and Buskirk 2013) and compete with or prey on martens. Skiers and staff are active during the majority of the day at high densities and during the night conducting grooming activities, creating a higher likelihood for marten-human encounters and their associated disturbances; such as decreased frequency of prey captures due to interruptions while hunting. Finally, while potential ski resort effects may appear to be greatest in winter, the permanent effects of habitat loss and fragmentation are present year-round, and may be increasing during the summer season as more resorts developing summer recreation programs (e.g., hiking, mountain biking). Ski areas may also have potentially beneficial effects on martens. Martens have been reported using anthropogenic food sources (e.g., dumpsters), using resort structures (e.g., chalets, buildings) as rest sites, and their tracks in snow are occasionally detected beneath lift lines where they may find discarded food items or prey that are attracted to them. Food available at ski areas, from humans, may also attract small mammals or support increased population sizes which, in turn, may provide food for martens. Evaluating the sum total of costs and benefits of ski areas on marten populations can best be achieved by contrasting the demographic health of populations found in ski areas to those in similar areas unaffected by ski operations. Evidence exists that martens are present at many of the ski resorts in the Lake Tahoe region. Surveys conducted at Heavenly ski resort have demonstrated that martens primarily occupy the central and southern portions of the resort, particularly during winter (Bartholomew & Associates 1993, Cablk and Spaulding 2002). Surveys detecting martens and sightings of martens have occurred on or near several other resorts in the region (e.g., Sierra at Tahoe, S. Yasuda pers. comm.; Alpine Meadows, K. Boatner pers. comm.; Homewood, K. Slauson pers. obs.). Although survey detections and sightings provide information on occurrence, occurrence

Load more