Northern distributional limit of Juniperus californica

Over expansive portions of North America, juniper dominated vegetation is afforded ‘formation’ status: that is, a dominant, zonal ecosystem characterized by a single species (dominant in biomass and of trophic cascades), extensive, climatically-correlated vegetation type on a continent-wide scale.  In California, a Juniperus californica community has not been recognized at the higher-syntaxon level: in southerly California, Thorne (1) did not distinguish a Juniperus californica vegetation type where it is most abundant.  Certainly at lower syntaxonomic levels (associations), J. california communities are of ecological interest. California juniper rarely forms extensive stands in the northerly part of its geographic range.

The geographic range of J. californica has been little discussed in classical conifer synchorological literature: Jim Griffin and Bill Critchfield did not map Junperus california (2) probably because these foresters considered it to be 'not a tree'.  Conifer distribution maps offered up by Little (3), using his characteristic method whereby a radius envelope was drawn encircling each known site, shows the range of J. californica becoming more discontinuous  northward in California.  The range map in Adams (4) is generalized.

I will leave aside the fact that southerly Junipers related to J. californica should probably be afforded taxonomic segregation (perhaps as subspecies):  J. cedrociana on Cedros Island;  J. ‘californica’ on Guadalupe Island, which is considered extirpated; might be distinct, given the density of unique endemics in that flora.  Others in far south Baja?

Of considerable interest is the single specimen attributed to J. californica from the Klamath River canyon, Siskiyou County (SD51279), fully 100 miles north of Ash Creek.  What species is this?  A Juniper plexus-nexus might be indicated in the Klamath-Siskiyou ‘knot’ which perhaps still has some untying to do: Juniperus californica var. klamathensis L.F. Henderson, described from near Mt. Ashland, and considered a synonym of J. occidentalis (4), is at the far westerly extent of that arid, cold-interior tree.  Also of note is a disjunct outlier also being called J. occidentalis (2) in Trinity County.  All of these, again, indicate a Klamath-knot that merits study to untie; Vasek (6) found some of these westerly outliers to be chemically distinct.

Sudworth (5) reported J. occidentalis from the Canyon Creek Lakes watershed in the Trinity Alps: Griffin & Critchfield (2) guessed this report to be Juniperus communis (of Sect. Juniperus):  this report needs field survey, as the Canyon Creek watershed obviously has its own entangled ‘Klamath knot” in the guise of Bochera serpenticola, Sedum paradisum and other narrow endemics which grow there.

Northern Limit at Ash Creek

The northerly distributional limit of J. californica is at the very head of the Sacramento Valley,  specifically at Ash Creek, east of Anderson, which is tributary to the Sacramento River just north of the Tehama County line.  The colony of J. californica is scattered within a foothill savannah matrix of Quercus douglasii and Pinus sabiniana on very shallow, stony, volcanic-derived ‘soils’.   Specimens attributed to another Ash Creek (specifically CAS349187) are incorrectly mapped.  Other far N specimens are mis-labeled (CAS515186), these are J. occidentalis.

The Juniperus californica stand can be seen along the county road (Ash Creek Road) for several miles beginning at the low hills that begin just east of the Sacramento River crossing at Balls Ferry.   The site has not burned in recent times, and many trees are large ‘bushes’ – that is, about 3-4 meters tall and multi-trunked. 

References

1. Thorne, R.F.  1976.  pp. 1-31 in Vegetation of Southern California.  Calif. Native Plant Soc.

2.  Griffin, J.R. & W.B. Critchfield. 1976 (supplement).  USDA Forest Service Res. Paper PSW-82

3.  Little, E.L.  1971.  Atlas of United States Trees. Vol. 1. USDA Forest Service Misc. Pub. 1146

4.  Adams, R.P.  2011.  Junipers of the World: the genus Juniperus.  3^rd ed.

5.  Sudworth, G.B.  1901.  Forest trees of the Pacific slope.  USDA.

6.  Vasek, F.C.  1966.  The distribution and taxonomy of three western Junipers.  Brittonia 18:350-372.