PREMISE Understanding edaphic specialization is crucial for conserving rare plants that may need relocation due to habitat loss. Focusing on Eriogonum crosbyae, a rare soil specialist in the Great Basin of the United States, we asked how site‐level variation among volcanic soil outcrops affected plant growth and population distribution. METHODS We measured emergence, survival, size, and biomass allocation of E. crosbyae seedlings planted in soils collected from 42 outcrops of actual and potential habitat. We also measured phenotypic variation in the wild, documented abiotic and biotic components of E. crosbyae habitat, re‐surveyed Nevada populations, and evaluated occupancy changes over time. RESULTS Plants responded plastically to edaphic variation, growing larger and allocating relatively more to aboveground tissues in soils with greater nutrient availability and growing smaller in soils higher in copper in the field and the greenhouse. However, the chemical and physical soil properties we measured did not predict site occupancy, nor was plant phenotype in the greenhouse different when plants were grown in soils from sites with different occupation status. We observed occupation status reversals at five locations. CONCLUSIONS Eriogonum crosbyae performed well in soils formed on hydrothermally altered rocks that are inhospitable to many other plants. Extirpation/colonization events observed were consistent with metapopulation dynamics, which may partially explain the patchy distribution of E. crosbyae among outcrops of potential habitat. While soil properties did not predict site occupancy, early life stages showed sensitivity to soil variation, indicating that seedling dynamics may be important to consider for the conservation of this soil specialist.

Soil specialists can have restricted distributions, and effective management in the face of land use change depends on a thorough understanding of the ecology of these unique plants. We investigated the ecology of Eriogonum tiehmii Reveal, a rare soil specialist, using pitfall traps, flower observations, and pollinator exclusion to assess arthropod communities in E. tiehmii habitat, the most common visitors to E. tiehmii flowers, and the importance of pollination for seed set. We collected soil from 21 occupied and unoccupied sites for analysis of physical and chemical characteristics, and conducted a greenhouse soil preference experiment to test how seeds and seedlings respond to soil variation. We also monitored tagged plants in extant populations, measuring survival, size, and reproductive output. Arthropod communities within and around E. tiehmii sites were abundant and diverse; each sample site contained numerous unique species, and there was high turnover in arthropod community composition over time. Open pollination significantly increased seed production, with beetles, wasps, and flies the most likely important pollinators.Reproductive output and size class distributions varied among wild populations, and soil properties differed between occupied and unoccupied sites. Occupied sites were, on average, lower in sulfur, zinc, potassium, and magnesium and, on average higher in boron, pH, and silt, among other differences, though there was high variation in these characteristics among sites.Seedlings demonstrated sensitivity to individual soil properties, and seedlings grown in soils from occupied sites had, on average, higher total biomass and higher root allocation than seedlings grown in soils from unoccupied sites. These preference tests suggest a "specialist" model of soil specialization rather than a "refuge" model, indicating that plants are not simply highly stress-tolerant, but are specifically adapted to their native soil types. While some unoccupied sites we tested were favorable for some life history stages, we did not identify unoccupied sites that could support both establishment and growth of E. tiehmii seedlings. Future work could consider the effects of biotic interactions such as plant competition and herbivores on plant growth, and employ

IntroductionRare plant species comprise >36.5% of the world’s flora and disproportionately support ecosystem function and resilience. However, rare species also lead global plant extinctions, and unique ecological characteristics can make them vulnerable to anthropogenic pressure. Despite their vulnerability, many rare plants receive less monitoring than is needed to inform conservation efforts due to limited capacity for field surveys.MethodsWe used field observations and geospatial data to summarize how 128 imperiled, rare vascular plant species in Nevada are affected by various threats. We assessed correlations between threats predicted by geospatial data and threats observed on the ground and asked how historic and current threats compare.ResultsThe most commonly observed threats were from recreation, invasive and non-native/alien species, and livestock farming and ranching. Threat prevalence varied by elevation (e.g., a greater variety of threats at lower elevations, greater threat from climate change observed at higher elevations) and land management. There was a 28.1% overall correlation between predicted and observed threats, which was stronger for some threats (e.g., development of housing and urban areas, livestock farming and ranching) than others. All species experienced extreme climatic differences during 1990-2020 compared to baseline conditions, with the most extreme change in southern Nevada. The average number of threats observed per occurrence increased by 0.024 each decade.DiscussionWhile geospatial data did not perfectly predict observed threats, many of these occurrences have not been visited in over 30 years, and correlations may be stronger than we were able to detect here. Our approach can be used to help guide proactive monitoring, conservation, and research efforts for vulnerable species.