Relevance

Osgood Swamp is a lake located near the base of Echo Summit, adjacent to the town of Meyers. Two separate fen sites have been confirmed on the west and south sides of the swamp (Sikes et al., 2011). Sphagnum fens are peat-forming wetlands that form when stable hydric soils allow a rate of organic matter production that is greater than the rate of decomposition, which over millennia leads to an accumulation of peat (Patterson and Cooper 2007, Weixelman and Cooper 2009). In environments with low summer precipitation like the Sierra Nevada, fens are sustained by groundwater input rather than precipitation. They are important sites of groundwater discharge and may serve as indicators of shallow aquifers (Cooper 1990).The conditions required for fens are very limited in mountain ecosystems, and fens occupy only 0.1 to 0.2 percent of the landscape in the Sierra Nevada (Wolf and Cooper 2015). Because fens form slowly over thousands of years, they are not easily restored once destroyed (Cooper et al. 1998), and they provide an important record of prehistoric climate and vegetation (Wolf and Cooper 2015). Fens have been identified by the U.S. Forest Service and in the Tahoe Science Plan, (Manley et al., 2010) as among the most sensitive habitat types in the Sierra Nevada. Fens are hotspots of biodiversity that support rare plants, insects, and small and large mammals. Vegetation in all wetland types, including fens, marshes and meadows plays an important role in recycling nutrients, trapping eroding soil, and filtering pollutants such as nitrates (Cooper and Wolf, 2006). In addition, fens figure prominently in nearly all scenarios of carbon dioxide-induced global climate change because they are major sinks for atmospheric carbon (Chimner and Cooper, 2002). A quantitative system for ranking the ecological integrity and quality of fens in the Sierra Nevada was used to assess the attainment status of fens at Osgood Swamp (Sikes et al. 2011). In the 2010 Lake Tahoe Region Fen Assessment, the western fen at Osgood Swamp received a conservation significance score of 27 out of 40, while the southern fen was one point lower due to its closer proximity to U.S. Highway 50. Elements that contributed positively to the rankings include the presence of rare plants and vegetation associations, and the uniqueness of the fens in terms of pH, elevation, and geology. Elements that detracted from the score include the presence of rodent burrows at the southern site and prevalent beaver activity around Osgood Swamp that could be affecting the hydrology, and causing higher water levels than in the past. Conservation significance scores of 26 and 27 are considered high when compared to the range of scores for fens in the Tahoe Region (18 to 30 points) and indicate that the natural qualities of the fens exist.

Human and Environmental Drivers

Any condition or activity that disturbs the hydrologic regime, nutrient levels, or alters plant composition, is a threat to the function of that fen (Cooper, 1990). Activities in general that threaten fens in the Sierra Nevada include timber harvest, mechanical fuel reduction treatments, road and trail construction, livestock trampling, off-road vehicles, ground and surface water pumping, and water pollution (Cooper and Wolf, 2006). All are regulated and managed in the Tahoe Region. At Osgood Swamp, illegal snowmobile use is concentrated on existing roads outside of the wetland, and a minimum 100-foot buffer around the water is enforced for adjacent mechanical fuel treatments. Hydrologic modification from beaver activity is also impacting this community. The two fens at Osgood Swamp are not easily accessible from the decommissioned U.S. Forest Service road on the west side of the swamp or any of the numerous user trails surrounding the swamp. In the summer, light recreational use from local hikers and cyclists is confined to the well-established trail network. In the winter, cross-country skiing and illegal snowmobile traffic have been observed, but generally confined to the roads surrounding the swamp (TRPA 2007). The 2006 Threshold Evaluation Report first noted high levels of beaver activity increasing water levels across the entire area, which altered the hydrologic conditions of the fen. Beavers were once thought to be non-native to the Sierra Nevada, but carbon dating of old beaver dams has shown that beavers were in the Sierra Nevada since AD 580 (James and Lanman 2012, Lanman et al. 2012). Beaver trapping eliminated beavers from the higher Sierra Nevada by mid-1800s. Beavers were reintroduced into the Lake Tahoe Region in 1938 in the vicinity of Meiss Meadows (Tappe 1942), and additional introductions may have occurred. Since then populations have expanded to many watersheds around Lake Tahoe. Viewing Google Earth historical images, the first notable beaver activity and extensive ponding in Osgood Swamp occurred before 2004. In 1940 Osgood Swamp was a swamp with observable channels and different patches of wetland vegetation. By 1969, a ditch had been constructed presumably to drain the swamp. Vegetation appears to be predominantly drier meadow. By 1992 a patch of trees had established in the center of the meadow. By 2004, the entire meadow was flooded, and the trees in the center and along the lake margin were dying. By 2007 the trees had fallen, and a treeless margin occurred along the west shore 20 to 120 feet from the lake edge. A series of beaver dams are visible at the lake outlet, and their lodge appears to have been moved from near the outlet to the east side of the lake in 2010 or 2011, perhaps due to the high water year. There is also a man-made structure that dams up water. There have been several years where the soil is exposed in a large portion of the lake (August 2012), and years that the lake has been very full (June 2011). It appears that the lake level fluctuates seasonally as well as annually. It is difficult to determine the desired condition of Osgood Swamp because of these changes. Historically, beaver may have ponded Osgood Swamp, and when it was exposed as a swamp, it may have been a result of the exclusion of the beavers, and now we might be seeing a return to natural conditions. Another theory is that in the process of installing a small dam and creating a deep channel to drain the swamp, human intervention created conditions suitable for beaver habitat, where it did not exist before. Extended drought and climate change could also negatively impact site hydrology and vegetation (Chimner and Cooper, 2002). Hydrologic change, which will likely be exacerbated by climate change, is predicted to be the largest threat to fen communities. Recent California based climate models predict a nine-degree Fahrenheit increase in temperature by 2100, and more conservative models predict a two to four-degree Fahrenheit increase in winter and four to eight-degree increase in summer (Safford et al., 2012a). Models are more variable for precipitation, but recent models for the Sierra Nevada predict similar to slightly less precipitation. Most models predict drier summer conditions, since more of the precipitation is predicted to come as rain, and snow melt-off will occur earlier in spring (Hayhoe et al. 2004, Dettinger 2005, Safford et al. 2012, Drexler et al. 2013). In the Lake Tahoe Region, these changes appear to be happening at an accelerated pace (Coats 2010). Snowpack is the dominant source of groundwater recharge (Earman et al. 2006), and since Sierra Nevada fen sustainability depends on groundwater, these climatic changes pose a severe threat (Drexler et al. 2013). Further, Sierra Nevada fens have relatively shallow peat depths, which make them highly susceptible to drying effects from increased temperature and/or reduced moisture (Drexler et al. 2013). Drexler et al. (2013) found that five Sierra Nevada fens had shrunk by 10 to 18 percent between 1951 and 2010, while at the same time mean minimum air temperature had increased and snowpack longevity and April 1 snow water equivalent had decreased. One soil sample collected in 1966 from “the center of the lake” was described in 1971 (Zauderer 1973). The study states: “The lake was approximately 100 meters in diameter, and presumably 1 meter deep before being drained in 1967.” The soil sample was composed of 60 cm of soily peat, clayey peat, and peat from rooty debris from surface to bottom of core respectively. A sample from 60 centimeters had a radiometric carbon date of 2,800 to 3,000 years before the present, resulting in a peat accumulation rate of 47 to 50 years/centimeter of peat (Zauderer 1973). The upper 23 centimeters had more mineral soil than the lower horizons, possibly indicating hydrologic changes. The current lake is approximately 190 by 270 meters in size, which is nearly triple the original size estimate. The soil samples and recent photos indicate that Osgood Swamp has fluctuated between a lake and a swamp. The most fibrous peat layers are from 58 to 152 centimeters, which suggests a change occurred just over 1,000 years ago.

Transportation Indicators

• Acres of Habitat Restored or Enhanced
• Parcels Inspected for Defensible Space