Rank Method Rank calculation - Biotics v2
Review Date2022-09-06
Change Date2022-09-06
Edition Date2022-09-06
Edition AuthorsHammerson, G., and E. Gaines (2022)
Threat ImpactHigh
Range Extent20,000-200,000 square km (about 8000-80,000 square miles)
Number of Occurrences81 - 300
Range Extent CommentsRange extends from the Cascade and Olympic mountains of northern Washington south to northern California, USA. Populations in the Olympic Mountains of Washington and the Trinity Alps, Mt. Shasta, and Mt. Lassen areas of California are notably disjunct from the primary distribution along the main Cascade axis (Pearl and Adams 2005). Historical locations at low elevations in Washington suggest that the species formerly may have been more broadly distributed (Leonard et al. 1993). Historical elevational range extended from around 400 to 2,500 meters; it is now found above 600 meters (Hallock and McAllister 2009, Pope et al. 2014). Populations in Lassen National Volcanic Monument at the southern end of the range appear to be extirpated (Pope et al. 2014).
Occurrences CommentsThis species is widespread throughout its historical habitat in Washington and can be abundant at some sites (Hallock and McAllister 2009). In Oregon, there are more than 100 occurrences, though not all of these are extant, and only 11 of them have a last observed date after 2000 (Pearl et al. 2009, Duarte et al. 2021, ORBIC 2022). Pope et al. (2014) reports 11 populations remain in California, mostly in the Klamath Mountains. It is apparently extirpated from Lassen Volcanic National Park, near the southern end of the species' range (Pope et al. 2014).
Threat Impact CommentsThreats are not fully understood, but their effects are likely interactive and vary by life stage (Alton and Franklin 2017, Cook et al. 2022). Threats are most well-documented at the southern end of the species' distribution in northern California, where declines have been the greatest (Piovia-Scott et al. 2011, Pope et al, 2014, Cole et al. 2016, Alton and Franklin 2017, Evelyn and Sweet 2018, Cook et al. 2022). Introduced predatory fish, habitat loss and degradation (from fire suppression and/or grazing), disease, UV-B radiation, air borne pollutants, and climate change are the greatest threats to this species (Fellers and Drost 1993, Pope et al. 2014, Cole et al. 2016, Evelyn and Sweet 2018, Duarte et al. 2021, Cook et al. 2022).
Livestock grazing can degrade habitat and alter hydrology, reducing available breeding habitat and reducing survival to metamorphosis (Pope et al. 2014, Cole et al, 2016). Grazing is widespread in the range of the Cascades frog, but numbers of livestock have been reduced compared to historical numbers (Pope et al. 2014). Grazing can degrade habitat by increasing sedimentation (Oregon Department of Fish and Wildlife 2016).
Higher elevation sites receive heavy recreational use, altering vegetation and soil structure, increasing sedimentation and modifying mudflats (Pope et al. 2014). Alpine meadow habitats are particularly prone to trampling (Pope et al. 2014).
Fire suppression activities, including drawing water from ponds, application of fire retardant, and construction of fuel breaks may harm populations, but the impact is unclear (Pope et al. 2014, Evelyn and Sweet 2018). Dense forests with high fuel loads as a result of fire suppression can lead to catastrophic wildfire, decreased downslope water inputs, altered peak flows, and increased sedimentation (Pope et al. 2014). Fire suppression on National Forests may have reduced open meadow habitat (Fellers and Drost 1993, Evelyn and Sweet 2018).
Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is found in Cascades frog populations throughout California and reduces juvenile survival (Piovia-Scott et al. 2011, Pope et al. 2014). The effect of Bd on juvenile survival varies by habitat type, suggesting an interaction between habitat, climate, and disease (Cook et al. 2022).
Egg masses are susceptible to mass die offs from water mold (Saprolegnia ferax) (Blaustein et al 1994, Kiesecker and Blaustein 1997). Nonnative fish are widespread rangewide and prey on Cascades frogs and compete with them for food resources (Pope et al. 2014, Cole et al, 2016, Thurman et al. 2022). Cascades frogs tend not to breed in wet meadows with nonnative trout present (Cole et al. 2016). The effects of predatory fish may also be interactive with other stressors such as climate change and disease (Pope et al. 2014). Removal of introduced fish resulted in increased apparent abundance of Cascades frog adults and larvae in Mount Rainier National Park (Larson et al. 2017).
Pollution is identified as a threat in in Oregon and Washington (Thurman et al. 2022). Air-borne pesticides drifting from California's Central Valley pose a threat to California populations, particularly those in the southern Cascades (Davidson et al. 2002, Pope et al. 2014). However, Davidson et al. (2012) found no difference in pesticide concentrations between these groups, and no correlation with population declines. Increased ultraviolet-B radiation due to ozone depletion is a threat, particularly at higher elevations (Alton and Franklin 2017). This threat interacts with other environmental factors, complicating threat assessment, but contributes to reduced hatching success, larval survival, and activity levels (Kiesecker and Blaustein 1995, Fite et al. 1998, Blaustein et al. 1994, Alton and Franklin 2017).
Climate change will result in altered hydroperiods (earlier drying) in Cascades frog breeding habitat. More severe winters may lead to reduced overwinter survival (Pope et al. 2014, Thurman et al. 2022). This threat is likely greatest in California's southern Cascades, where populations are already small and isolated (Pope et a. 2014). Increased drought associated with climate change will result in altered hydroperiods and reduced habitat for Cascades frogs (Pope et al. 2014, Oregon Department of Fish and Wildlife 2016, Thurman et al. 2022), Increases in drought may affect susceptibility to Bd (Cook et al. 2022). In northern California, shortened hydroperiods were strongly associated with reduced survival to metamorphosis (Cole et al. 2016).