Aspidotis densa ecology

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 (https://geologyportal.dnr.wa.gov/2d-view), Oregon (https://gis.dogami.oregon.gov/maps/geologicmap/), and California (https://www.researchgate.net/figure/Map-of-California-showing-counties-and-outcrop-areas-of-serpentinized-peridotite-after_fig1_228475957 and https://maps.conservation.ca.gov/cgs/gmc/). 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:
https://www.inaturalist.org/observations/118201996
https://www.inaturalist.org/observations/118201108
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 (https://www.inaturalist.org/observations/118199458).

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

[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)