Serpentine Geoecology of Eastern North America: A Review

Abstract

Serpentine outcrops are model habitats for geoecological studies. While much attention has been paid to serpentine outcrops worldwide, the literature on eastern North American serpentine and associated biota is scant. This review examines the available literature, published and unpublished, on geoecological studies conducted on serpentine in eastern North America, from Newfoundland through Québec and New England south to Alabama. Most serpentine outcrops in the region have been mapped, but there have been few intensive mineralogical and pedological investigations. The limited soil analyses available suggest elevated levels of heavy metals such as Ni, near-neutral pH values, and Ca:Mg ratios , 1, characteristic of serpentine soils worldwide. Botanical studies to date have largely focused on floristic surveys and the influence of fire exclusion and grazing on indigenous vegetation. To date, 751 taxa of vascular plants belonging to 92 families have been reported from serpentine outcrops in the region. Two taxa, Agalinis acuta and Schwalbea americana, are federally endangered in the United States while many others are listed as rare, endangered, or imperiled in one or more states or provinces. Globally, six species, Adiantum viridimontanum, Minuartia marcescens, Pycnanthemum torrei, S. americana, Scirpus longii, and Symphyotrichum depauperatum are listed as imperiled (G2) while one species, Agalinis acuta, is listed as critically imperiled (G1). Cerastium velutinum var. villosissimum is the only recognized serpentine endemic plant for eastern North America while Adiantum viridimontanum, Aspidotis densa, M. marcescens, and S. depauperatum are largely restricted to the substrate. Based on current distributions, we propose that A. viridimontanum and M. marcescens be considered endemic to serpentine substrates in eastern North America. Studies on cryptogams list 165 species of lichens and 146 species of bryophytes for the region. None of the species found appear to be restricted to the substrate. Compared to other regions of the world, ecophysiological and evolutionary investigations are scant. Biosystematic investigations are restricted to the taxa Adiantum aleuticum, C. velutinum var. 22Rhodora [Vol. 111 villosissimum, and S. depauperatum. Plant-soil relations, especially the capacity to hyperaccumulate metals such as Ni and the ecological consequences of metal accumulation, are also under explored. One report from eastern Canada lists Arenaria humifusa, M. marcescens, Packera paupercula, and Solidago hispida as hyperaccumulating Ni although the findings have yet to be confirmed by subsequent investigations. Overall, serpentine geoecology in eastern North America remains largely unexplored.

Bryophyte diversity in Californian grasslands in relation to substrate quality, exotic vascular plants and disturbance

“…In contrast, serpentine sites dominated by native vascular plants were characterized by colonist shade-intolerant bryophyte species typical of rocky and bare soils (e.g., Didymodon vinealis and Syntrichia princeps). These effects of serpentine on bryophyte assemblages in Californian grasslands resemble the effects seen in other regions (Briscoe et al 2009;Cleavitt et al 2009;Rajakaruna et al 2009). …”

Interactions between soil biota and the effects on geomorphological features

“…bottae is known to survive and have increased densities on serpenitic (ultramafic) soils (Proctor and Whitten, 1971), which have very high Mg:Ca ratios and generally support a very specialized community of plants (Rajakaruna, 2009). These soils are prone to landslides because of the nature of ultramafic soils (Brideau et al, 2007), but no information indicates whether pocket gophers contribute to causing instability or increasing stability in these soils.…”

Serpentine ecosystem responses to varying water availability and prescribed fire in the U.S. Mid‐Atlantic region

“…Serpentine soils are typically shallow and macronutrient poor with low calcium to magnesium ratios, high heavy metal content (i.e., chromium, cobalt, and nickel), and low soil water holding capacity (Walker 1954, Proctor and Woodell 1975, Brady et al 2005, Rajakaruna et al 2009). Prior research indicates that nutrient limitations impose significant restrictions on serpentine plant productivity, such that addition of another limiting resource, specifically water, does not lead to increased growth (Going et al 2009, FernandezGoing andHarrison 2013).…”

“…Ecological studies of serpentine ecosystems in eastern North America are limited and provide a poor understanding of how the serpentine syndrome is manifest in the region's serpentine barrens (Rajakaruna et al 2009). In particular, little is known of ecosystem productivity and its response to environmental drivers in the serpentine barrens of the U.S. Mid-Atlantic region (i.e., northern Maryland and southeastern Pennsylvania).…”

“…Gray), Symphyotrichum depauperatum Fernald (G.L. Nesom)), as well as rare plants and animals (Latham 1993, NRCS 2013a, Rajakaruna et al 2009). Management is necessary in these barrens, as the lack of historical disturbance agents (i.e., human-ignited fires and grazing) has led to forest encroachment and substantial land area losses (Tyndall 1992, Tyndall and Hull 1999, Latham 2008, Latham and McGeehin 2012.…”