Friday, April 10, 2009

Three Plants now missing from Yosemite Valley

Yosemite Valley is arguably the most visited place on Earth. With three million visitors cramming into an area of about 10 square-miles, it is no wonder that the flora of Yosemite Valley should suffer. Exactly how it has suffered has not been subject of sufficient study.
How has the Valley flora changed? The topic has been addressed, peripherally, by Heady & Zinke 1978, and it is well known from photographs that woody vegetation has historically been on the increase in the Valley and that meadow and herbaceous communities have declined.
However, we can draw on another historical account to illustrate the hypothesis that human impacts have caused some plants to disappear from the Yosemite Valley scene. In 1891, Katharine Brandegee published an essay “Flora of Yo Semite” in Zoe [Vol. 4, 155-167]. The Brandegee paper is a narrative describing the conspicuous. Brandegee states specifically the paper is based on specimens collected by the California Botanical Club in 1891, and on notes by J.M. Hutchings.

Pacific Yew (Taxus brevifolia)
Taxus brevifolia is at or near its southerly geographic limit in the Yosemite region. The documented present-day southern distributional limit for Pacific Yew is in the Stanislaus River watershed at Calaveras Big Trees State Park, Calaveras County, about 30 miles [and two major river canyons] to the north. A single specimen (UC334344, originating from the Lemmon herbarium, is labeled as “Yosemite V, 1874, Muir”, and if taken on face value, indicates that yew might have been extirpated from the Yosemite Valley flora. Pacific Yew has not been documented by resurveys (P. Rundel. 1969. Madroño 19: 300; Griffin & Critchfield 1976 did not map it as it is not a ‘forest tree’) by resurvey. Brandegee (p. 160) states “the Yew (Taxus brevifolia) grows near the water in the cañon of the Merced”, and [also in discussion of Torreya california] states “neither this tree of the last quite reaches the valley”. Taxus brevifolia has not been documented as extant in the Park. Although the canyon of the Merced is rarely traveled, it is more likely that if an extant occurrence remained hidden in the less frequently traversed canyon regions, it nonetheless would have drawn someone’s attention. Thus, with doubt, Pacific Yew (Taxus brevifolia) can be listed as extirpated from the Park.

Dutchman’s pipe (Aristolochia california)
On p. 158: Dutchman’s-pipe (Aristolochia California) grows near Tissack bridge. The flowers are seldom collected because they appear before the leaves…”. No extant site for Aristolochia is known in the Valley. The stated upper elevation limit given in the Jepson Manual is 700 m [2300 ft], which would make any occurrence in the Valley an upper outlier. It is not unlikely that Aristolochia occurred there: in cultivation [based on the horticultural profile in the Jepson Manual, it might be able to survive in the Valley climate, which is snowy but also relatively mild in terms of extreme freezes: hard freezes to -12 C are rare].

The location of Tissack bridge is also in question: that placename does not appear on any map. However, early maps of the valley label the road from Happy Isles north toward Mirror Lake as Tisscak Avenue, hence it is likely that Tissack bridge is present day Happy Isles Bridge [note the small b of bridge, indicating perhaps a non-specific reference to the bridge on Tissack Avenue….?]

Fawn-lily (Erythronium sp.)
on p. 166 Brandegee states “The purple dog-tooth violet (Erythronium purpurascens) is found on the south side of the Valley , from the upper iron bridge to Tooloolaweack Cañon” Tooloolaweack is an older place name for present day Illilouette Canyon. Exactly which species of Erythronium was collected remains uncertain. Any specimen was destroyed in the 1906 earthquake and fire which consumed most of the herbarium at the California Academy of Sciences, where Brandegee was a curator. I have come to consider that as curator, Katherine Brandegee filed specimens according to published names available in Botany of California [1876-1880] and other publications [Gray and Watson papers in Proc. Amer. Acad.] This practice extended to using those published names in print, in works such as “Flora of Yo Semite”. This, it is my opinion, that Brandegee’s application of the name Erythronium purpurascens to a plant from Yosemite Valley was a misapplication, based on the fact that Erythronium purpurascens does not grow this far south in the Sierra. She was simply using a folder name – that is, the only published name available at the time, and a folder in which several then undescribed species would have resided.

The Yosemite fawn lily may be either of four species known from the central Sierra, all endemics: E. taylori, E. hartwegii, E. pluriflorum and E. tuolumnense. The latter two species have yellow flowers, although it is not impossible that the specimen did not preserve flower color, it is more likely that the Yosemite plant was a plant with white or mixed white-yellow tepals. That leaves as candidates only the former two species. Of these, E. hartwegii is confined to the foothills, below 2000 feet [Note: syn. E. ‘multiscapoideum’ (Kellogg) Nelson & Kennedy, a long used - and incorrectly spelled as ‘multiscapideum’ – name. Before the type illustration was destroyed in the 1906 earthquake and fire at CAS, K. Brandegee (Proc. Cal. Acad. 1 (Ser. 2), 128-151. 1883) confirmed this name as a synonym of E. purpurascens S. Waston, a fact overlooked by monographers (cf. Matthew 1992, Applegate 1935, Allen 2001). This leaves only E. taylori, which is presently known extant on Pilot Ridge, at 4400 ft, nearly the same elevation as the Valley. Pilot Peak was partially within Yosemite National Park until a little known boundry adjustment in 1905-1906.

Until an extant occurrence of Erythronium is found in the Valley, we cannot be certain which taxon grew there. However, the stated location, which is essentially along the trail from Happy Isles to Vernal Falls, is so well visited that I can only assume that a very small occurrence was long ago eliminated by visitors picking flowers.

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