Ecological dynamics

Abiotic factors
This ecological site occurs on subalpine valley floors and hillslopes with slopes ranging from 5 to 30 percent. Soils have an umbric epipedon and are moderately deep to granitic bedrock or a densic horizon, typically with loamy skeletal textures. Threadleaf sedge is strongly dominant, and forms dense sods. Parry’s rush (Juncus parryi) is a common associate. Forb diversity and abundance is low on this site due to strong competition from dense threadleaf sedge roots. There is typically low cover of small statured whitebark pine trees. This site is considered a dry meadow, where groundwater is at depths greater than 1 meter, and precipitation or runoff is the main source of water (Klikoff 1965, Benedict 1983, Ratliff 1985a, Fites-Kaufmann et al. 2007, Weixelman et al. 2011).

Threadleaf sedge dry meadows are widespread in subalpine and alpine habitats in the Sierra Nevada and often occur on warm, dry south-facing aspects on gravelly soils (Ratliff 1974,Vankat and Major 1978, Burke 1982, Jackson and Bliss 1982, Ratliff 1985b, Hauser 2006, Fites-Kaufmann et al. 2007). These meadows receive early season moisture from runoff, snowmelt and precipitation (Weixelman et al. 2011). Threadleaf sedge is a cool season species, which uses the early season moisture on this site for growth, then goes dormant for the summer dry period (Ratliff 1974). Threadleaf sedge forms a dense sod, with a dense mat of roots that extend 1.5 m into the soil, or to root restriction for shallower soil, and which makes it difficult for other species to compete. However, bare patches of soil, gravel, and bedrock within the sod are important microsites for forb diversity (Jackson and Bliss 1982). Forb diversity increases with disturbance such as grazing or rodent activity (Klikoff 1965).

Disturbance/Ecological factors
Drought, livestock grazing, and global climate change are the primary disturbances impacting this ecological site. Although lightning strikes may initiate fire, the low fuel loads of this site mean that fire is highly unlikely to carry.

Historically these meadows would have been lightly to moderately grazed by native wildlife, including bighorn sheep, deer, and small mammals (Ratliff 1982). Starting in the late 1800’s and until the 1930s they were intensively grazed by sheep (e.g. Ratliff 1974, Vankat and Major 1978, Benedict 1983, Ratliff 1985a, Odion et al. 1988), and most contemporary Sierra Nevada meadows are either recovering from grazing or are still grazed by pack animals, with few if any pristine examples (Benedict 1983). Damage from sheep grazing is still apparent in threadleaf sedge meadows, with decreased foliar cover, increased bare ground, pedestalling of sod, and erosion of soil and sod (Vankat and Major 1978, Ratliff 1982, 1985a, Odion et al. 1988), with only patches of vegetation in some meadows (Vankat and Major 1978, Odion et al. 1988). In the 1970s a sample of 10 shorthair sedge meadows in Kings Canyon National Park had a mean foliar cover of 29 percent, while an island meadow presumably free of grazing had a foliar cover of 70 percent, and four times the standing biomass of previously grazed sites (Ratliff 1974). A comparison of historic photos showed little recovery in 70 years. We measured an average foliar cover of 45 to 55 percent in meadows judged to be in good condition. Although sheep have not grazed these meadows since the 1930s, recreational pack stock continue to do so. A study of the impacts of pack animals on shorthair sedge meadows in Yosemite showed a mean reduction in biomass of 18 percent, with a seven percent increase in bare ground and a decline in relative graminoid cover (Cole et al. 2004). The authors recommend utilization below 35 percent.

An ongoing pattern of warming and decreased snowpack is predicted under global climate change scenarios for the Sierra Nevada (e.g Hayhoe et al. 2004, Safford et al. 2012). Recent California based climate models predict a 9 degree F increase in temperature by 2100, and more conservative models predict a 2 to 4 degree F increase in winter and 4 to 8 degree increase in summer (Safford et al. 2012). Models are more variable for precipitation, but recent models for the Sierra Nevada, predict similar to slightly less precipitation. Most models agree that summers will become drier, since more of the precipitation is predicted to come as rain, and snow melt-off will occur earlier in spring (Hayhoe et al. 2004, Safford et al. 2012). Alpine areas have been called bellwhethers for global climate change impacts (e.g. Seastedt et al. 2004), due to a highly specialized flora and fauna that may not compete well with a lessening of harsh environmental conditions, and no higher elevations to retreat. However, unidirectional change may not be realistic. Microtopographic variation may allow for within site or more local migrations (Gibson et al. 2008, Spasojevic et al. 2013). Xeric community types such as shorthair sedge meadows, may expand into previously moister locations with increased warming and reduced precipitation (Spasojevic et al. 2013). Long-term studies of dry meadows in Colorado have shown these dry systems to be fairly resilient to change, with impermanent transitions occurring in response to annual variations in climate (Johnson et al. 2011, Spasojevic et al. 2013). However, while communities are not being lost, there is an overall trend of increased diversity as species from lower elevations move up, and in time, these species may outcompete the locals (Johnson et al. 2011, Spasojevic et al. 2013). In this ecological site, shorthair sedge would likely remain dominant, but the associated forbs and trees that are more strongly adapted to high elevations might be lost. Since the specific changes that will occur with global climate change are currently unknown for this site, climate change impacts are not included in the state-and-transition model.

All tabular data listed for a specific community phase within this ecological site description represent a summary of one or more field data collection plots taken in communities within the community phase. Although such data are valuable in understanding the phase (kinds and amounts of ground and surface materials, canopy characteristics, community phase overstory and understory species, production and composition, and growth), it typically does not represent the absolute range of characteristics nor an exhaustive listing of species for all the dynamic communities within each specific community phase.