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1. Spring ephemeral herb species in temperate deciduous forests are active above-ground only briefly each year. This study tested experimentally how two countervailing constraints – cold and darkness – influence the phenology of six spring herb species. 2. Dormancy of underground structures, maintained by cold temperatures in a growth chamber, was broken at six 25-day intervals from January or February to June in two consecutive years. Upon emergence, survival and flowering were measured on cohorts grown outdoors. Shade cloth was added at the time of normal canopy closure. 3. Cardamine concatenata, Dicentra cucullaria, Erythronium albidum and Trillium recurvatum had no or low 2-year survival in the two or three earliest cohorts and no or low survival in the latest cohort, relative to their natural cohort. Allium canadense and Claytonia virginica had survival in all cohorts. Flowering never occurred in the first two or three cohorts for three species and never occurred or declined in later cohorts in all species. 4. Despite widely differing emergence dates, senescence was completed within a 40-day period soon after shade was imposed for all cohorts for all species. Consequently, leaf life span became shorter as date of emergence was delayed among cohorts. 5. In general, the brief growth period of spring herb species is an adaptation to avoid winter cold and late-spring canopy shade. These constraints are species-specific and differ for survival and flowering for some species. Claytonia virginica is the most tolerant among the species to a wider range of conditions. 6. Synthesis. Knowing that cold and shade constrain a plant's non-dormant period is important because of the significant role plant phenology plays in responses to climate change.

Spring ephemerals in the Central Appalachians are a key component of deciduous forest communities and can be indicators of shifting phenology due to climate changes in this ecosystem. The objectives of this study were to (1) determine if there have been any changes in date of flowering for the Cutleaf Toothwort (Cardamine concatenata) and Yellow Trout Lily (Erythronium americanum) in West Virginia over the last 111 years; (2) determine which climatic factors affect the blooming date of these perennial, spring ephemeral wildflowers; and (3) evaluate the effect of elevation on changing blooming dates using herbarium specimens and photographs from 1904 to 2015. Both species are widespread throughout the woodlands of eastern North America. Both species have significantly advanced their spring flowering over the last century (x̅ = 0.91 days/decade). Spring temperature was the strongest predictor of blooming date (2.91 and 3.44 days earlier/1 °C increase in spring temperature, respectively). Flowers at < 500 m elevation bloomed earlier and demonstrated a stronger shift in flowering date over time than flowers at > 1000 m elevations. Lower elevations, higher spring and winter temperatures, and low amounts of precipitation were associated with earlier spring flowering. This research demonstrates the plasticity of phenological response to a variety of climatic variables, the usefulness of using herbarium specimens to reconstruct flowering dates over a topographically variable area, and the contrasting effects of climate change on high elevation regions of West Virginia.

The introduction of novel plant species to new habitats may have consequences for native herbivores. We examined the impact of Alliaria petiolata, a Eurasian invader of forest understories and edges in North America, on adult oviposition behavior and on larval preference and the performance of Anthocharis midea, a univoltine butterfly that specializes on plants in the Brassicaceae. We compared the usage of A. petiolata by this butterfly to that of one of its common native hosts, Cardamine concatenata, and additionally explored the impact of drought and larval age on the larval success of these hosts. In the field, adults oviposited on the native host preferentially earlier in the season, but they strongly preferred A. petiolata later in the season and laid more eggs overall and in multiples more often on this plant. Larvae strongly preferred to feed on leaves of C. concatenata over A. petiolata in the laboratory and survived to pupation at a high rate on it. Conversely, larvae fed little and died when offered A. petiolata. Larvae preferentially chose tissues of droughted C. concatenata over well-watered plants, but drought stress had no impact on larval mass and survival to pupation. Larvae showed no preference for droughted or non-droughted A. petiolata and while drought stress tended to extend survival on this plant, all larvae still died on it. Older larvae were no better at feeding and surviving on A. petiolata than young larvae. Our results indicate that A. petiolata currently serves as an ecological trap for A. midea, being both highly attractive to ovipositing adults yet lethal to larvae. This effect could cause both local declines in the abundance of this butterfly and drive selection for the altered behavior of adults and larvae to either avoid or better tolerate this plant.

Abstract Spring ephemerals are wildflowers found in temperate deciduous forests that typically display aboveground shoots for a period of 2 months or less. Early spring, before the canopy leaves out, marks the beginning of the aboveground growth period where ephemerals acquire nutrients and resources via aboveground tissues. Several studies have shown that spring ephemeral reproduction is affected by spring temperature, but few have looked at how weather conditions of the current and previous seasons, including precipitation and temperature, influence aboveground growth. Here, we examine the response of a spring ephemeral community in a temperate hardwood forest to weather conditions during their current and previous growing seasons. For 15 years we estimated percent cover of each species within our community. We highlighted five dominant spring ephemerals within this community: wild leek (Allium tricoccum), cutleaf toothwort (Cardamine concatenata), spring beauty (Claytonia virginica), squirrel corn (Dicentra canadensis) and trout lily (Erythronium americanum). We compared changes in cover on both a community and species level from 1 year to the next with average precipitation and temperature of the year of measurement as well as the year prior. We found precipitation and temperature influence a change in cover at the community and species level, but the strength of that influence varies by species. There were few significant correlations between plant cover in the current year and temperature and precipitation in the 30 days preceding measurement. However, we found significant correlations between plant cover and precipitation and temperature during the previous spring; precipitation and cover change were positively correlated, whereas temperature and cover change were negatively correlated. Overall, cooler, wetter springs lead to an increase in aboveground cover the next year. Learning how individual species within a forest plant community respond to weather conditions is a crucial part of understanding how plant communities will respond to climate change. We examined the response of a spring ephemeral community in a temperate hardwood forest to weather conditions during their current and previous growing seasons. For 15 years we estimated the percent cover of each species within our community. We compared changes in cover on both a community and species level from 1 year to the next with average precipitation and temperature of the year of measurement as well as the year prior. There were few significant correlations between plant cover in the current year and temperature and precipitation in the 30 days preceding measurement. However, we found significant correlations between plant cover and precipitation and temperature during the previous spring; precipitation and cover change were positively correlated, whereas temperature and cover change were negatively correlated. Overall, cooler, wetter springs lead to an increase in aboveground ephemeral cover the next year.

Showy invasive plants can reduce pollinator visitation to native plants, resulting in a reduction of seed-set in insect-pollinated species. Seed set in native plants may also be reduced due to the presence of foreign pollen. Alternatively, additional floral resources provided by invasive plants may increase pollinator activity, and facilitate pollination of native species. Ranunculus ficaria is a perennial herb invading deciduous forests of the eastern United States. It produces many showy flowers that may influence pollinator activity in heavily invaded habitats. We compared pollinator visitation rates, stigma pollen loads, and seed production of two sympatrically flowering, entomophilous native species ( Claytonia virginica and Cardamine concatenata ) between habitats invaded by R. ficaria and uninvaded habitats. We found significantly higher pollinator activity (visits to plots) in invaded plots. We also found significantly higher per flower visitation rates to C. virginica in invaded plots. Claytonia virginica stigmas from invaded habitats had more conspecific pollen resulting in more seeds per capsule in invaded areas. There was more conspecific pollen on C. concatenata stigmas in invaded compared to uninvaded habitats, but there were significantly more seeds per silique in uninvaded habitats. Our results indicated that this invasive species increases pollinator activity and conspecific pollen deposition on sympatrically flowering native ephemerals, but may have differential effects on native seed production. Management options should consider the facilitative effects of this species on pollination services, as well as the possible negative competitive effects.

The Novel Weapons Hypothesis predicts that invasive plants excel in their new ranges because they produce novel metabolites to which native species possess little resistance. We examined the novelty of the phytochemistry of the Eurasian invader, Alliaria petiolata, in North America by comparing its phytochemical profile with those of closely related Brassicaceae native to North America. We examined the profile and/or concentrations of glucosinolates, alliarinoside, flavonoids, cyanide, and trypsin inhibitors in cauline leaves of field-collected A. petiolata, Arabis laevigata, Cardamine concatenata, C. bulbosa, and C. douglassii. Cyanide and the glucosinolates and flavonoids produced by A. petiolata were detected only in A. petiolata. Trypsin inhibitor activity was highest in A. laevigata, intermediate in the Cardamine species, and lowest in A. petiolata. The phytochemical profile of A. petiolata was distinct from those of four closely related and/or abundant Brassicaceaeous species native to North America, providing support for the Novel Weapons Hypothesis.

Principal coordinate analysis using Gower's similarity coefficient and canonical discriminant analysis were performed using morphological data to assess species distinctness in the Cardamine concatenata alliance, comprising the eastern North American dentarias. The results of an overall principal coordinate analysis of the alliance using quantitative and qualitative characters revealed distinct and separate clusters that correspond to five previously recognized species (C. angustata, C. concatenata, C. diphylla, C. dissecta, C. maxima). One additional taxon, C. incisa, was found to group closely with the C. diphylla cluster. In a second principal coordinate analysis including only individuals from C. diphylla and C. incisa, both are supported as distinct morphological entities. Canonical discriminant analysis of only above-ground quantitative characters was less effective in distinguishing previously recognized taxa, in keeping with the emphasis on qualitative characters in previous taxonomic treatments of the group. Cardamine incisa (Eames) Schumann (pro hybr.) is raised to the rank of species. A key to the species of the Cardamine concatenata alliance is provided.

Phosphorus (P) and nitrogen (N) foliar resorption during senescence was examined in Cardamine concatenata (a spring ephemeral), Trillium flexipes (a spring herb), and Smilacina racemosa (a summer herb) along contiguous forest topographic gradients in southwestern Ohio. Overall, mean apparent (and proportional) foliar P resorption ranged from -0.13 mg/g (-8.3%) for S. racemosa to 1.79 mg/g (68.1%) for C. concatenata. Mean apparent foliar N resorption ranged from 11.25 mg/g in S. racemosa to 37.71 mg/g in C. concatenata, while mean proportional N resorption ranged from 23.3% in T. flexipes to 62.4% in C. concatenata. Analysis of variance indicated significant differences among species and topographic positions for both P and N resorption. The significant topographic position effect for P resorption reflected greater overall resorption in the bottomland positions while that for N resorption reflected greatest resorption in uplands and bottomlands and lower resorption in slope positions. We suggest that the significant differences among species may reflect their phenological patterns and photosynthetic adaptations while differences among topographic positions primarily reflect soil nutrient availability and moisture status.