Sunday, June 2, 2013

Herbivore caused mortality in the rare Lewisia kelloggii (Montiaceae)

Lewisia kelloggii is endemic to California.  Populations are limited to the mountains: the Sierra Nevada, Cascade Mountains, and Klamath Ranges.  Lewisia kelloggii regardless of subspecies is a Forest Sensitive Plant for California National Forests.

Having made this observation many decades ago, and recently seen it again, I here describe mortality in the rare plant Lewisia kelloggii caused by herbivory.   Summarizing, the starchy roots of Lewisia kelloggii are excavated by animals seeking sustenance, resulting in mortality of the Lewisia.

NDDB draft EO#63 (Peddler Hill, Amador County)
Years ago, I observed golden-mantled ground squirrel (Callospermophilus lateralis) excavate and carry away roots of a population of Lewisia kelloggii.  Oh that’s the time I did not think what the particular significance of this observation might be.

NDDB draft EO#68 (vicinity Hull Creek, Tuolumne County, 30 May 2013)
I observed the same excavations at one subpopulation of L. kelloggiii.  About 90% of the plants in one subpopulation segment had been excavated, the roots consumed, and the dead rosettes were scattered about on the ground.  Most of the remaining plants were non-flowering, presumable juvenile plants. [top photo).  Many corporeal remains of Lewisia were observed here, many left in their graves, some remains were blown away for a few feet.  

NDDB draft EO#84 (vicinity Sentinel Dome, Mariposa County, 30 May 2013)
On the order of 20% or so of the occurrence was subject to herbivory.  The attached photo shows excavations, with dead or dying plants of L. kelloggii. [bottom photo].  Again, clearly, rodents were excavating plants seeking out the roots for food.


The observed pattern of rarity of L. kelloggii – widely dispersed but nowhere common – may be directly a function of herbivore modulation of population success.  Factors related to trophic cascades governing the abundance of squirrels and their raptor predators may thus play a significant role in the endangerment status of L. kelloggii.  Land management elements which affect this trophic cascade therefore are of interest given the Forest Sensitive status of L. kelloggii.

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