Aspidotis densa ecology

Apparently lowland Aspidotis in WA can regrow short sterile fronds in the fall. e.g.

Note - most of my observations about soil are out there somewhere in the literature but in very difficult to synthesize manners or places...

Aspidotis densa (Serpentine Fern) is usually described as unusually tolerant of serpentinite/ultramafic/peridotite derived soils (hereafter called "serpentine") but also appearing in other locations. No doubt this is to some extent true, but I suspect that a lot of the "non-serpentine" Aspidotis are on smaller serpentine exposures or other rocks/soils with unusual composition. There is a striking general correlation of observation number on iNaturalist and known outcrops of serpentine rock (including small ones that are not always easy to find in web searches) throughout WA, OR, and CA (and the Frontenac outcrop in Quebec).

For example, the dense population in Washington Park WA, the high density of sitings in parts of Marin County CA, some (but not all) patches through the Sierra Nevada, and the Sumas Mountain cluster in northwest WA, and a disjunct cluster in Quebec, all correspond to serpentine outcrops (in addition to obvious correlations in the Wenatchee and Klamath/Siskayou mountains). In California there are many known serpentine outcrops in the southern part of the state that appear to have no Aspidotis but I assume this is from other factors, especially general climate (warmer and drier). These include outcrops in Santa Clara, San Benito and Monterey Counties.

Explained clusters (on or very close to known ultramafic rock):
  • The dense cluster on Grasshopper Mountain BC (about 8 km west of the town of Tulameen in south central BC) is ultramafic, but is probably also oversampled.
  • The clusters in the Teanaway Wenatchee Mountains.
  • The Sumas Mountain cluster in northwest WA, near Canadian border
  • The large cluster in the Marin County coastals (Mt Tamalpais and running approximately NNW) follows the ultramafic outcrop very nicely.
  • The cluster about 8 km NNW of Occidental (CA coastals) is ultramafic.
  • The cluster about 15 km W of Healdsburg (CA coastals) is ultramafic.
  • The cluster on the shore of Lake Sonoma (CA coastals) is ultramafic.
  • The cluster W and NW of Trinity Lake (CA coastals) is ultramafic, and is approx. the southern edge of the huge Klamath-Siskayou ultramafic complex.
  • The large diffuse (probably just undersampled) cluster extending SW from Mount Shasta to Sawtooth Mountain is generally ultramafic and is approx. the eastern edge of the huge Klamath-Siskayou ultramafic complex.
  • The clusters in the Klamath-Siskayou region (assumed all are ultramafic, not inspected in detail)
  • The loose group running S and SE from Mount Lassen is the beginning of the Sierra Nevada clusters, some of which are and some of which are not ultramafic (e.g. around Lake Tahoe).

    In several places where I have made observations, there are local correlations as well, where well developed soils (probably ultimately serpentine derived but well weathered and enriched with organic material and perhaps partially leached of free heavy metals?) support few or no Aspidotis whereas nearby "barrens" support lots of Aspidotis. I am provisionally assuming that the failure of Aspidotis to grow in well developed soils is due to competition rather than direct failure to grow.

    I need to locate better maps of serpentine outcrops, but there are good ones for Washington (, Oregon (, and California ( and Actually I suspect these maps are not that helpful, since the WA state map around the Teanaway Wenatchees is clearly missing ultramafic sections. I suppose it is mostly failure to map small outcrops. I have made much progress in assigning serpentine regions, which will be presented as part of the project "Serpentine Plants of the Western United States".

    I also wonder where there is some other soil syndrome unrelated to documented serpentine outcrops, on the basis of a very restricted zone (approximately 500 meters) along the north shore of Lake Cushman with very large Aspidotis densa populations but no documented serpentine that I could find:
    The edges of this Aspidotis zone appear to be well defined, with Aspidotis abrupty no longer present on adjacent rocks despite all other obvious conditions and flora patterns being the same. I hypothesize (guess) that heavy metal concentration is responsible (likely nickel, iron, or cobalt). An alternative is very low concentrations of calcium or potassium or a high magnesium/calcium ratio, also characteristic of ultramafic rocks, or some combination of these. The eastern edge of the zone may not be as well defined, as the open rock habitat drops off close by. The western edge seems quite clear (

    Any geology expert or person with access to soil chemistry testing would be welcome to comment or help. :-)

    Unexplained clusters:
  • cluster on Lake Cushman WA - my data
  • top of Little Si WA - my data
  • cluster on west face below ridge at Larrabee state park (Chuckanut range) some accessible from roads, though extremely steep slopes.
  • cluster in the Columbia River gorge just east of White Salmon WA
  • cluster near Lake Blanche UT (Wasatch Mountains)
  • several sites on the south end of Vancouver Island Canada, the largest one running about 12 km west from the western outskirts of Victoria.
  • various sites in the Sierras, though I have not directly observed them and don't know much about the rocks. The Sierra clusters include one just south and southeast of Lake Tahoe and one around Lake Spaulding near Yuba Pass (though with ultramafic rock not far away).

    [resolved mostly I don't understand the CA Sierra serpentine - some maps show lots of small outcrops in the Sierras but the main official CA map shows almost none east of the divide (e.g. near Lake Tahoe). It does show a NNW to SSE strip on the west side of the Sierra Ridge, running from about (-121.240, 40.100) to about (-120.760, 39.100), which probably accounts for some Aspidotis but there aren't obvious clusters.]

    I am currently writing software to analyze observation "density" for taxa (research grade observation number normalized to total observations in some form of surface grid). If anyone knows of similar efforts that would be good too. Downloading and working with iNaturalist data is quite straightforward but I need better databases for things like temperature, precipitation, rock types, and non-U.S. elevation (the U.S. I can already handle).

    Observations to do:
    Oyster Dome Trail, south Chuckanut
    Scatter Creek Trail to first ridgeline
    Lake Ann Van-Epps approach
    Tucquala Peak
    Cashmere Mountain, lower
    Miller Peak
    Ingalls Creek again (lower)
    trails around Johnny Creek Campground (Johnny Creek, Mac Creek)

  • Publicado el agosto 30, 2022 05:43 TARDE por jhorthos jhorthos


    Thanks for this useful journal entry. I have generally seen A. denda in serpentine soil areas. It would be mighty interesting to understand what is going on in areas such as Little Si or Lake Cushman. Look forward to observing this and other species in serpentine areas.

    I did a quick search and found one paper that might be useful

    Look forward to further discussion and exploration.

    Publicado por brewbooks hace más de 1 año

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