When rare plants are distributed across a range of habitats, ecotypic differentiation may arise requiring customized conservation measures. The rate of local adaptation may be accelerated in complex landscapes with numerous physical barriers to gene flow. In such cases, examining the distribution of genetic diversity is essential in determining conservation management units. We investigated the distribution of genetic diversity in the federally threatened Camissonia benitensis (Onagraceae), which grows in two distinct serpentine habitats across several watersheds in San Benito, Fresno, and Monterey Cos., CA, USA. We compared genetic diversity with that of its two widespread relatives, C. contorta and C. strigulosa, and examined the potential for hybridization with the latter species. Genotyping results using seven heterospecific microsatellite markers indicate that differentiation between habitat types was weak (F ST = 0.0433) and in an AMOVA analysis, there was no significant partitioning of molecular variation between habitats. Watersheds accounted for 11.6 % of the molecular variation (pairwise F ST = 0.1823–0.4275). Three cryptic genetic clusters were identified by InStruct and STRUCTURE that do not correlate with habitat or watershed. C. benitensis exhibits 5–11× higher inbreeding levels and 0.54× lower genetic diversity in comparison to its close relatives. We found no evidence of hybridization between C. benitensis and C. strigulosa. To maximize conservation of the limited amount of genetic diversity in C. benitensis, we recommend mixing seed representing the three cryptic genetic clusters across the species’ geographic range when establishing new populations.

Where serpentine soils exist, variation in soil properties affects plant species distribution at both coarse and fine spatial scales. The New Idria (California, USA) serpentine mass has barren areas, supporting only sparse shrub and tree islands, adjacent to areas of densely-vegetated serpentine chaparral. To identify factors limiting growth on barren relative to vegetated serpentine soils, we analyzed soils from barren, shrub-island within barren, and vegetated areas and foliage from shrub-island and vegetated areas. We also grew Ceanothus cuneatus (native evergreen shrub), Achillea millefolium (native perennial forb), and Bromus madritensis ssp. rubens (invasive annual grass) in soils from barren and vegetated areas amended factorially with N, K, and Ca in a pot study. In well-watered pots, biomass was greater by 5-, 14-, and 33-fold for Ceanothus, Achillea, and Bromus, respectively, on vegetated-area-collected soils than on barren-collected soils, indicating a strong soil chemistry effect. Although field soil data suggested nutrient deficiency and not heavy metal toxicity, pot study plant data indicated otherwise for two of the three species. On barren-collected soils, only Ceanothus responded positively to added N and Ca and did not show greater foliar Mg or heavy metal (Fe, Ni, Cr, Co, Zn) concentrations than on vegetated-area-collected soils. Ceanothus maintained lower root Mg and heavy metal (Fe, Ni, Cr, Co) concentrations on barren soils and translocated less heavy metal (Fe, Ni, Cr, Co, Mn, Cu) from roots to foliage than Achillea and Bromus. Achillea and Bromus showed significant log-log biomass relationships with foliar Ca:Mg (+), Mg (-), and heavy metals (Fe, Ni, Cr, Co, Mn, Cu, Zn) (-), while Ceanothus showed relationships only with Ca:Mg (+) and Mg (-). The New Idria barren-vegetated pattern appears to be maintained by different factors for different species or functional types— low Ca:Mg ratios on barrens for all species tested, high heavy metal concentrations for Achillea and Bromus, and low macronutrient (N) concentrations for Ceanothus. Combined data from this and other studies suggest high heavy metal concentrations more strongly affect herbaceous than woody species, contributing to variation in species distribution on serpentine soils.

This chapter focuses on methods used in the restoration and revegetation of stressful edaphic environments. It begins with methods used in the restoration or revegetation of nonserpentine soils and then describes how the same approaches are applied to the restoration or revegetation of serpentine soils. The discussion highlights soil and vegetation manipulation methods used to restore partially degraded serpentine ecosystems and then focuses on three steps—physical site stabilization, substrate amendment, and plant and microbial materials selection—that are critical to successful revegetation of severely degraded serpentine ecosystems. The chapter concludes by evaluating how well serpentine ecosystems serve as model environments for restoration and revegetation studies.

This chapter focuses on how distinct soil types have resulted in ecotypic differentiation and adaptation. It begins with evidence for ecotypic differentiation in chemically stressful edaphic environments, including saline soils and metalliferous mine tailings. The chapter then proceeds to highlight ecotypic differentiation in response to serpentine soils. The discussion includes a summary of the adverse physical and chemical characteristics of serpentine soils, key plant morphological and physiological mechanisms involved in serpentine soil tolerance, how ecotypic differentiation leads to the origin of new species, and an extensive review of plant intraspecific variation found within serpentine ecosystems worldwide. The chapter concludes by summarizing major trends in plant adaptation to serpentine soils as demonstrated by examples of intraspecific variation.

Centuries of mining economically valuable minerals from serpentine have left a legacy of drastically disturbed landscape. Asbestos and nickel-laterite mining from serpentine is estimated to have degraded 11,130 and 19,070 ha, respectively, in 18 countries. Increasing mineral extraction, fueled by increasing global demand for industrial commodities, will continue to have devastating impacts on serpentine landscapes. Simultaneously, increasing environmental awareness is motivating nations to balance economic advancement with environmental protection. Revegetation of landscapes degraded by mining provides a way to address these issues. This review highlights some advances of the past decades in serpentine revegetation and ecology, and provides a framework of concepts, including physical stabilization, substrate amendment, and plant-materials selection, by which drastically disturbed serpentine substrates may be revegetated.

Release rates of recently fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) from non-exchangeable interlayer sites in 2:1 silicate minerals were determined for decomposed granite (DG) saprolites from three locations in California, USA. Recently-fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) release from the DG substrate was quantified by extracting diffused \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) with H-resin, as well as a native, annual grass Vulpia microstachys. The \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) release data varied with via the method of extraction, which included H-resin pre-treatments (Na+ or H+) and V. microstachys uptake (mycorrhizal inoculated or uninoculated). After 6 weeks (1008 h), more \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) was recovered from fixed interlayer positions by the H-resins as compared to uptake by V. microstachys. The H+ treated H-resins recovered more released \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) (≈94 mg \({\text{NH}}^{{\text{ + }}}_{{\text{4}}} - {\text{N}}\;{\text{kg}}^{1} \) or (12%) of total fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \)) in two of the three DG samples as compared to the Na+ treated resins, (which recovered ≈70–78 mg \({\text{NH}}^{{\text{ + }}}_{{\text{4}}} - {\text{N}}\;{\text{kg}}^{{{\text{ - 1}}}} \) (or 9–10%) of the total fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \)). The V. microstachys assimilated 8–9% of the total fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) with mycorrhizal inoculum as compared to only 2% without a mycorrhizal inoculum, over the same time period. The fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) release kinetics from the H-resin experiments were most accurately described by first order and power function models, and can be characterized as biphasic using a heterogeneous diffusion model. Uptake of both the 15N and ambient, unlabelled N from the soils was closely related to plant biomass. There was no significant difference in percent of N per unit of biomass between the control and mycorrhizal treatments. The findings presented here indicate that observed, long-term \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) release rates from DG in studies utilizing resins, may overestimate the levels of fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \) made available to plants and microorganisms. Additionally, the study suggested that mycorrhizae facilitate the acquisition and plant uptake of fixed \( {\text{NH}}^{{\text{ + }}}_{{\text{4}}} \), resulting in markedly increased plant biomass production.

Restoring native grassland along roadsides can provide a relatively low-maintenance, drought-tolerant and stable perennial vegetative cover with reduced weed growth, as opposed to the high-maintenance invasive annual cover (requiring intensive mowing and herbicide treatments) that dominates most Sacramento Valley roadsides. A survey of long-established roadside native-grass plantings in Yolo County showed that once established and protected from disturbance, such plantings can persist with minimal maintenance for more than a decade, retaining a high proportion of native species. The survey also showed that each species of native perennial grass displays a microhabitat preference for particular roadside topographic positions, and that native perennial grass cover is negatively affected by disturbance.

A series of lab and greenhouse studies were undertaken to understand how Cu and Zn toxicity influences Bromus carinatus (Hook and Arn.) growth, to what degree an organic amendment (yard waste compost) may reduce Cu and Zn bioavailability in Cu–Zn minespoil and promote plant growth in combination with fertilizer, and how the vertical distribution of compost in the minespoil influences rooting depth. Root Cu and Zn toxicity thresholds were determined to be 1mgL−1 and 10mgL−1 in solution, respectively. The compost amendment had exceptionally high Cu and Zn binding capacities (0.17 and 0.08g metal g C−1, for Cu and Zn, respectively) that were attributed to high compost humic and fulvic acid concentrations. Maximum plant biomass was achieved when minespoil was amended with compost and fertilizer in combination. Fertilizer alone had no effect on plant growth. Mixing compost into the minespoil was essential to promote adequate rooting depth.

Subgrade serpentine substrates are exceptionally difficult to revegetate due to multiple limitations including low N, P, and K, low Ca:Mg molar ratios, high levels of heavy metals including Ni, Cr, and Co, low organic matter, low CEC, and low water holding capacity. To examine the influence of plant origin on the success of the revegetation of serpentine substrates, granite and serpentine accessions of Achillea millefolium were grown on subgrade serpentine substrate amended with yard waste compost, slow-release NPK fertilizer, and/or CaSO4 · 2H2O (gypsum). The goals of this study were to: (1) identify the substrate amendment combination that maximized establishment of A. millefolium on serpentine substrate, (2) compare seedling establishment, survival, and growth of the serpentine and granite A. millefolium accessions in order to determine if a serpentine edaphic ecotype of A. millefolium exists and if this ecotype is superior to the granite accession for the establishment of vegetation on serpentine substrate and (3) if a serpentine edaphic ecotype of A. millefolium does exist, what physiological features with respect to mineral nutrition convey a higher tolerance of serpentine for this ecotype than the nonserpentine ecotype. Seedling establishment, survival, and growth were greatest for A. millefolium when the subgrade serpentine substrate was amended with 30% (v/v) compost and 220 mg kg substrate−1 each of N, P, and K. The serpentine A. millefolium accession displayed a greater tolerance of the subgrade serpentine substrate, serpentine topsoil, and the amended subgrade serpentine substrate than the granite accession. Higher capacity of the serpentine A. millefolium accession for selective Ca translocation from roots to the shoot resulted in a significantly higher shoot Ca:Mg molar ratio than the granite accession and appeared to be the most important physiological feature conveying greater tolerance of the serpentine accession for serpentine substrates.

Soil and plants were sampled throughout winter and spring near a perennial stream traversing a restored mine site in a winter–rainy climate. Within 1m of an acidic reach of the stream, soil had pH 3–5 and 50–100μg/g “bioavailable” copper (extractable with 0.01M CaCl2). Soil 2–3m from the stream had pH 5–8 and lower (less than 3μg/g) bioavailable copper. “Oxide-bound” copper (extractable with 2N HCl) was 50–100μg/g at most locations. Copper concentrations in the shoots of field-collected Bromus carinatus declined from 20μg/g in winter to 2μg/g in spring at all sampling sites. A similar temporal pattern was found in plants grown under controlled conditions. Thus B. carinatus has a developmental program for control of shoot copper concentration, causing a seasonally-varying pattern of copper phytoaccumulation over a large range of copper availability in the soil.

Serpentine soils limit plant growth by NPK deficiencies, low Ca availability, excess Mg, and high heavy metal levels. In this study, three congeneric serpentine and nonserpentine evergreen shrub species pairs were grown in metalliferous serpentine soil with or without NPKCa fertilizer to test which soil factors most limit biomass production and mineral nutrition responses. Fertilization increased biomass production and allocation to leaves while decreasing allocation to roots in both serpentine and nonserpentine species. Simultaneous increases in biomass and leaf N:P ratios in fertilized plants of all six species suggest that N is more limiting than P in this serpentine soil. Neither N nor P concentrations, however, nor root to shoot translocation of these nutrients, differed significantly between serpentine and nonserpentine congeners. All six species growing in unfertilized serpentine soil translocated proportionately more P to leaves compared to fertilized plants, thus maintaining foliar P. Leaf Ca:Mg molar ratios of the nonserpentine species were generally equal to that of the soil. The serpentine species, however, maintained significantly higher leaf Ca:Mg than both their nonserpentine counterparts and the soil. Elevated leaf Ca:Mg in the serpentine species was achieved by selective Ca transport and/or Mg exclusion operating at the root-to-shoot translocation level, as root Ca and Mg concentrations did not differ between serpentine and nonserpentine congeners. All six species avoided shoot toxicity of heavy metals by root sequestration. The comparative data on nutrient deficiencies, leaf Ca:Mg, and heavy metal sequestration suggest that the ability to maintain high leaf Ca:Mg is a key evolutionary change needed for survival on serpentine soil and represents the physiological feature distinguishing the serpentine shrub species from their nonserpentine congeners. The results also suggest that high leaf Ca:Mg is achieved in these serpentine species by selective translocation of Ca and/or inhibited transport of Mg from roots, rather than by uptake/exclusion at root surfaces.

Barren, subgrade serpentine substrates are difficult to revegetate due to N, P, and K deficiencies, low Ca:Mg molar ratios, potentially high levels of heavy metals including Ni, Cr, and Co, low organic matter, low CEC, and poor water holding capacity. Several large, bare roadcuts exist in the North Coast Ranges along the west coast of California, USA. Substrate was collected from a large roadcut that has remained barren for more than a decade despite conventional surface amendment with NPK fertilizer and seeding with a mix including nonserpentine grasses and herbs. Although serpentine plant communities have been studied globally in great detail, very little information exists on how to effectively restore these communities after drastic disturbance (removal of topsoil and loss of biological activity). This rhizotron study examined how surface layering and mixing yard waste compost into serpentine substrate affected biomass production, rooting distribution, and tolerance of native, as well as invasive grass species that grow on serpentine. Roots of less serpentine-tolerant species became necrotic upon contact with the serpentine substrate in the layered compost application treatment. The roots of highly serpentine-tolerant species, however, displayed a superior tolerance to the serpentine substrate and were able to grow through its entire depth. Mixing the compost into the serpentine substrate significantly improved the Ca content of the growing medium, allowing the less serpentine-tolerant species to root through the entire depth. Although the compost surface layer treatment promoted growth of the highly serpentine-tolerant species in the serpentine substrate, mixing the compost amendment into the substrate would also permit additional desirable revegetation species to become established.

Summary Limited information exists on approaches to effectively revegetate severely disturbed, barren, subgrade (unconsolidated parent material) serpentine substrates. Additionally, little is known about the invasion potential of exotic grasses from highly invaded non‐serpentine environments into adjacent, relatively uninvaded serpentine environments following restoration efforts that use substrate nutrient enrichment to accelerate revegetation. This study investigated approaches to the revegetation of subgrade serpentine substrates with native, serpentine‐tolerant grass species while limiting the establishment and reproduction of invasive annual grass species. Biomass production was measured for two native serpentine perennial grass species and both biomass and seed production (fitness) were measured for one native annual and two invasive annual grass species. All species were grown on subgrade serpentine substrate amended with garden (yard) waste compost, slow‐release nitrogen (N), phosphorus (P) and potassium (K) fertilizers and CaSO 4 2H 2 O (gypsum) in both glasshouse and field environments. The primary goals of this study were to: (i) determine how substrate amendment with compost changed with time and (ii) identify the substrate amended combination that maximized native grass species biomass and seed production while limiting the productivity of invasive annual grass species. Compost amendment of the subgrade serpentine substrate greatly increased plant‐available N, P, K and calcium (Ca) levels, decreased plant‐available heavy metals, and increased the cation exchange capacity. Substrate concentration remained low for up to 60 days following compost amendment but then increased more than six‐fold in the 120 days thereafter. No other substrate properties changed substantially over a period of 180 days. Amendment of the serpentine substrate with 30% volume compost per volume substrate, and 220 mg each of N, P and K per kg substrate, maximized biomass and seed production of the native grass species. This amendment level, however, resulted in an undesirable increase in biomass and seed production (fitness) of invasive annual grass species, exceeding that of the native species. Synthesis and applications. Revegetation of drastically disturbed, barren, subgrade serpentine substrates with native, serpentine‐tolerant plant species can be successfully achieved with a combination of yard waste compost (organic) and slow‐release (inorganic) fertilizer amendment. Enrichment of low‐fertility serpentine substrates to promote native plant growth, however, may encourage invasion of undesirable plant species into the native plant community, leading to habitat degradation. Therefore, aggressive control methods may be required to prevent invasion of exotic species into the revegetation community.