Serpentine Soils: from Microbes to Landscapes

Friday, October 21 at 10:00-11:40 am, Oak Room

Session Description: Serpentine soils, high in heavy metals and low in nutrients, give rise to specialized plant communities adapted to thriving in these harsh conditions. In this session we show how serpentine soils shape the plants and lichens that inhabit them at multiple scales, including effects via microbes, seeds, pollinators, and regional-scale biogeography.

Session Chairs: Marina LaForgia (University of California, Davis, Davis, CA, USA) and Jesse Miller (University of California, Davis, Davis, CA, USA)

19.1 Plant affinities for serpentine soils in California: an updated database

Jesse Miller (Stanford University, Stanford, CA, USA)

We present an updated database that documents levels of plant taxon association with ultramafic (“serpentine”) substrates in the California flora. This database reflects recent taxonomic changes consistent with the second edition of the Jepson Manual (TJM2) and more recent updates to the Jepson eFlora, and includes additional species that were not previously documented as serpentine associates. We also include serpentine-associated species that have been described since the publication of TJM2 and are not yet incorporated in the eFlora. A number of taxa were removed from the Safford et al. (2005) database due to new ecological information or taxonomic changes. As before, the new database presents information on rarity, geographic distribution, taxonomy, and lifeform. Based on our new database numbers and TJM2’s list of California endemic species, the percentage of California endemic full species that are +/- restricted to ultramafic substrates has risen to 14.7%. Of 255 total endemic taxa in our database (including strict and “broad” endemics), 148 (c. 60%) come from only ten plant families, concentrated mostly in one or two genera per family. The North Coast and Klamath Ranges continue to support more serpentine endemics than the rest of the State combined. The previous version of the database has been widely used in biodiversity research and conservation management, and we hope that this improved and updated version will prove as valuable.

19.2 Serpentine lichens: regional and local patterns of assembly, and the challenge of context

Michael Mulroy (California Polytechnic State University, San Luis Obispo, San Luis Obispo, CA, USA), Nishanta Rajakaruna (California Polytechnic State University, San Luis Obispo, San Luis Obispo, CA, USA)

Serpentine and other ultramafic substrates are widely known for their unique vascular plant communities that result from the harsh conditions presented by ultramafic substrates. Lichens of ultramafic substrates, however, have received comparatively little attention, and interestingly do not appear to share most of the characteristics – high levels of endemism, distinct growth forms, metal hyperaccumulation, to name a few – commonly observed in ultramafic vascular plant communities. At the same time, studies of ultramafic lichens provide evidence for several patterns and characteristics. These include the presence of disjunct populations, consistent mixes of acidophytic and basiphytic lichen taxa, and clear differentiation in species composition between ultramafic and adjacent non-ultramafic rock and soil habitats. Here we present some results of a quantitative comparative study of saxicolous lichen communities of serpentine and sandstone outcrops on the central California coast. Our study investigates the relative importance of abiotic factors, including substrate elemental composition, microhabitat, and climate, that contribute to saxicolous lichen assembly. In addition, we present on several notable range extensions and records of rare lichen taxa that have resulted from our sampling. Lastly, we will review some apparent characteristics of ultramafic lichen assemblages at local and regional scales within California to help contextualize the results of our research.

19.3 The effects of invasion on serpentine grassland plant-pollinator mutualisms

Rebecca Nelson (University of California, Davis, Davis, CA, USA), Paul Aigner (University of California McLaughlin Reserve, Lower Lake, CA, USA), Susan Harrison (University of California, Davis, Davis, CA, USA), Fernanda Valdovinos (University of California, Davis, Davis, CA, USA)

Plant-pollinator mutualisms contribute to biodiversity and ecosystem function. Invasive species, however, can alter the structure and function of plant-pollinator mutualisms. We investigated how an invasive grass species and an invasive wildflower influenced the diversity, abundance, and structure of serpentine grassland plant-pollinator interactions. The invasive Aegilops triuncialis is a grass that can tolerate serpentine, while the invasive wildflower Vicia villosa grows on non-serpentine grasslands in close proximity to serpentine. At the University of California McLaughlin Reserve, we collected floral visitation data for serpentine plant-pollinator interactions. We found that both species had differing effects on native species. The invasive grass decreased the abundance of flowering plants, leading to reduced pollinator diversity and abundance. The invasive wildflower attracted rare native pollinators and had a distinct community of long-tongued pollinators compared to native serpentine wildflowers which were mostly visited by short-tongued pollinators. Both invasive species influenced the structure of plant-pollinator interactions. Invasive species can alter the structure and function of serpentine plant-pollinator interactions but through differing mechanisms.

19.4 Do seed traits and resource availability predict persistence of seeds in a Serpentine plant community?

Elise Elwood (University of California, Davis, Davis, CA, USA)

Grasslands are threatened by nutrient deposition, land use change, and changing patterns in precipitation as our climate shifts. Relating traits to species fitness is useful for prioritizing conservation and restoration efforts. However, seed traits, vital traits in grasslands where plants spend much of their lives in the soil seed bank, have been largely understudied except for seed mass. Seed dormancy and variable life history strategies allow individuals to reduce the risk of germinating in a bad year and failing to reproduce. However, there are separate risks associated with “hanging out” in the soil. There are seed predators (granivores, insects, fungi) in addition to lost viability. Past studies in Serpentine grasslands show that drought can increase relative abundance of native species in the seed bank and that the colimitation of nutrients and water maintains diversity and native cover. Further, shifting resource availability changes community composition of a seedbank. This study investigates if seed traits (mass, shape, coat thickness, permeability, C:N ratio) are correlated with seed persistence in the seedbank and if this shifts with water and nutrient availability. This project uses the relative abundance of species in a soil seed bank of control plots or plots exposed to added nutrients, added precipitation, or both from lush and harsh serpentine grasslands. Seeds from ~70 species were collected at the site and used to measure trait data. Initial results indicate that seeds with a lower seed mass and a higher carbon to nitrogen ratio are more abundant in the seed bank over time. Interestingly, there is little impact of added precipitation or nutrients on the relationship between seed traits and seed bank abundance. This work will help illuminate which seed traits are most important for seed persistence in a soil seed bank and inform the conservation and restoration of diverse grassland systems.

19.5 Fire history in adjacent mixed conifer forests with soils derived from serpentine and andesite

Scott Stephens (University of California, Berkeley, Berkeley, CA, USA)

Serpentine-derived soils are characterized by high levels of iron and magnesium, low levels of many essential plant nutrients, and the presence of toxic trace elements. These harsh soils give rise to a unique and diverse assemblage of plant species. California’s serpentine flora is considered one of the richest in the temperate zone and consists of hundreds of species that are largely or entirely confined to serpentine substrates. In addition to challenging chemistry, serpentine soils are shallow and rocky, with low water-holding capacity which also contributes to their low productivity. Ecotones derived from abrupt soils changes over a few meters are common in serpentine areas. How fires once burned in this environment has not been explored. A hypothesis is fire frequency would be less in serpentine areas because plant productivity would be lower limiting surface fuel accumulation when compared to adjacent areas with more productive soils. We investigated this question by sampling 6 fire history plots that spanned the ecotone described above in the northern Sierra Nevada near Meadow Valley in Plumas County, California. A total of 57 fire scarred trees, stumps, and down logs were collected from ponderosa pine, incense-cedar, and Jeffrey pine trees of which 46 were cross dated using standard dendroecological techniques. The fire record began in approximately 1650 and the last fire recorded varied from 1810 to 1893 depending on the site sampled. Plots with soils derived from serpentine experienced fewer fires but the median fire return intervals did not vary greatly across the ecotone. Areas with serpentine derived soils experienced frequent fire regimes, this provides important information for the conservation of the ecosystems in these areas, including their endemic flora.