Thursday, July 31, 2008

Fen at Pat Yore Flat, Nevada County

the fen is a shrubby site (above)

the little white heads of R. alba are distinctive (below)

Pat Yore Flat

Fens are odd, azonal, habitats that are in California known to support a variety of circumpolar, northern Hemisphere oroboreal (sensu Webber) taxa. Our fens are the southerly stragglers barely hanging on, remnant of Pleistocene abundance. In general, fens and bogs in the Sierra have not enjoyed much direct attention from botanists. Most sites are not described in detail. The most comprehensive fen overview is David Cooper’s report “Fens of the Sierra Nevada” which is mandatory reading on the topic.

Because Cooper & Wolf (2004) had reported Rhynchospora alba (CNPS List 2) from this location, and because there were no Consortium or CNDDB records for of R. alba from this location (including the pending file) I paid a visit.

Pat Yore Flat is located right along Forest Road 50, which I accessed via Highway 20 through Washington, thence up Forest Road 31, Nevada County (39.41409/-120.70702, T18N R11E Section 23; 6100 ft. Graniteville USGS quadrangle). The origin of the name is uncertain (Durham 2000 “Place Names of California’s Gold Country” ; Gudde 1969).

The flat is situate in the South Fork Yuba River drainage; the entire vicinity is mapped as granitic rocks. The flat is a gently sloping surface inclined about 5% facing southerly. The fen at this site is extensive, covering 100 ha or so, with general spring/seep discharge over an extensive area. I did not spend sufficient time to explore the entire fen.

Like an old fashioned waterbed, peat filled openings of the fen have a ‘quaking’ character, which is more typical of bogs formed via primary succession in lakes (i.e. Grass Lake, Luther Pass or Little Willow Lake, Lassen Volcanic NP). The depth and age of the peat deposits in this fen are a curiosity: are they Tioga stage (glacial) in age (i.e. >14 KYA?). A coring study is suggested, because I assume the quaking nature of the site indicated deep peat deposits which might yield a valuable chronology.

The water discharge into the fen is relatively sweet (I got a conductivity of only 10┬ÁS), and the bog is moderately acid (a hand held grab sample pH was low as 5.5, but did not control for the low-ionic water problem). Bogs are pH <5>