Agricultural land-use legacies remain persistent determinants of plant-community composition, despite extended periods of recovery in postagricultural forests of New York. We surveyed the composition of vascular plant species for 33 paired residual (unconverted) and secondary (postagricultural) forest sites across three physiographic regions in New York to assess the recovery of residual forest species in secondary successional stands. There were 169 vascular plant species recorded among the 33 study sites. The residual stands exhibited slightly greater mean (± SE) species richness (26.8 ± 1.7 species per site) than secondary-interior (21.4 ± 1.2, P = 0.001) and secondary-edge (24.1 ± 1.6, P = 0.02) zones. Plant communities differed across the three physiographic regions (P = 0.001) and by stand history within regions (P = 0.004). Of the vascular plant species occurring at our sites, 22 (13%) were indicators of residual forest stands and 27 (16%) were indicators of secondary, postagricultural forest stands. Within 10 to 25 m of the historic field-forest ecotones, the relative frequencies of many residual woodland indicator species fell to 0–20% of the maxima they attained in the residual stands. Ant-dispersed (myrmecochorous) taxa represented 23% of residual and 0% of secondary forest indicators and exhibited lower migration rates (P < 0.001) than plants possessing other diaspore dispersal modes (anemochory, zoochory, barochory). In addition to plant dispersal mode, we found pH and forest-floor depth to be important determinants of plant species. Our results indicate that impoverishment of plant communities in postagricultural forests represent a regionally pervasive phenomenon with important resource management implications in the eastern USA. Residual woodlands remain important source populations for recovery of herbaceous species in postagricultural landscapes. However, given the slow historic recovery rates that we and others have observed in postagricultural secondary forests, in addition to other contemporary factors potentially inhibiting dispersal and establishment (e.g., herbivory, pollinator disruptions, invasive species), it seems likely that active restoration efforts are needed to promote full recovery of diverse, native temperate-forest herb communities.

Amur honeysuckle (Lonicera maackii (Rupr.) Herder) is recognized as one of the most important invasive species in the Ohio River Valley. Since 2012, outbreaks of the native pathogen honeysuckle leaf blight in the region have been observed, coincident with the report of high levels of L. maackii dieback in an open-grown stand in northern Kentucky. The purpose of this study was to quantify the extent of dieback in the area and to determine whether dieback was also present in stands growing under forest canopies (forest-understory). Data were collected from plots placed along transects for eight open-grown and six forest-understory sites in northern Kentucky and nearby southwestern Ohio in 2014–2016; diameters at stump height (25 cm) of all live and dead woody stems were measured in the plots. For L. maackii in open-grown stands, 30% and 23% of stem density and basal area, respectively, were dead, which was higher than that seen for associated shrubs and small trees; it was also higher than that reported in the 1980s for L. maackii in open-grown stands in the region. Mortality in the larger-size classes was higher than that seen in the 1980s. By contrast, stem mortality of L. maackii in forest-understory stands varied little from that seen in the 1980s. Basal area mortality was similar to associated species. The possible role of leaf blight in the decline of open-grown L. maackii requires further investigation.

Traits associated with root morphology and nutrient uptake rate may contribute to the competitive ability of invasive species by determining their access to soil nutrients and their ability to extract those resources. Here, we tested the hypotheses that (a) exotic woody shrubs would be superior belowground competitors for nitrogen in heterogeneous soil resulting from key aspects of root architecture and (b) larger plants would be superior belowground competitors. We tested these hypotheses using two native shrubs, Rubus allegheniensis and Viburnum dentatum, and two invasive exotic shrubs, Rubus phoenicolasius and Berberis thunbergii, all four of which can become abundant in plant communities in the eastern United States. We grew replicate plants from each species with interspecific competitors, with intraspecific competitors, and individually in a randomized layout in a greenhouse in two temporal blocks. Each experimental container had a central soil patch amended with ¹⁵N-labeled litter. We measured above- and belowground growth, root morphology, and nitrogen uptake to assess the effects of intra- and interspecific competition on plant growth and nitrogen uptake. All species grew better in the second temporal block, but we did not detect any differences in the competitive ability or root traits for exotic versus native species; rather, plant size was the key trait that predicted competitive effects. Both Rubus species, which capitalized on the extended growing season offered by our greenhouse conditions, were stronger competitors and typically larger plants than B. thunbergii and V. dentatum. Both Rubus species exerted measurable competitive effects on other species, resulting in decreased aboveground size of competitors by 50% or more relative to control plants, but did not routinely decrease ¹⁵N uptake or root biomass of competitors. When competing with Rubus, leaf C:N ratios of all species except R. phoenicolasius were greater than when grown alone, suggesting that large Rubus plants did decrease the total nitrogen available to competitors. Our data suggest that belowground competitive ability in shrubs may be more closely associated with plant size and growth rate than plant origin. In addition, plant species that exhibit plastic growth phenology, such as those in the genus Rubus, may gain a competitive advantage during years with warmer autumn months by extending their growing seasons, facilitating their invasion and establishment in new habitats.

Very little is known about how emerald ash borer will affect hardwood swamps, which often have a large ash component compared to upland forests. The aim of this research project was to investigate the current status of ash swamps that have become infested with emerald ash borer and make predictions about the future state of these forests. We surveyed three hardwood swamps in southern Michigan that varied in the amount of ash present (12.4%–58.8% basal area), which appears to affect how these communities will change as a result of emerald ash borer. Our analyses indicate that the two swamps with the least amount of ash will likely experience a proportional increase in surrounding trees, while structure of the site with the most ash will be altered in the future and may transition to a forest that is strongly influenced by shrub-like individuals as well as non-ash canopy trees.

The population structure of invasive species is determined both by species-specific breeding strategies and by region-specific conditions and events during the history of invasion. In this context, we investigate the role of human land-use policy on the gene flow within population of the widespread invasive tree, Ailanthus altissima. We predicted that genetic diversity would be elevated in urban environments and reduced in exurban, and that human mediated dispersal would allow propagules to break geographic isolation. Six populations of A. altissima, divided evenly among urban, exurban and suburban sites, were surveyed using a set of eight microsatellite loci. A total of 276 individuals were sampled. Populations were assessed for partitioning of genetic variation, gene flow between sites, and genetic cluster estimation. Effective population size based on genetic variation was also modeled using Bayesian Markov chain Monte Carlo simulations. Despite a strong propensity for clonal growth, the microsatellite data revealed no evidence of clonal reproduction at the population level. Gene flow between sites was found to be independent of geographic distance; instead, gene flow was correlated with the level of human traffic at a site. Genetic diversity was found to generally increase in correlation to human development; however, reduced admixture at managed sites suggests that land management practices were effective at inhibiting gene flow into managed sites.

Systematic field surveys were conducted for Narthecium americanum in the New Jersey Pine Barrens in order to determine its status and distribution. Surveys were carried out for 61 extant populations (98% of total) and 12 historic/extirpated populations (60% of total), and in approximately 180 km of potential habitat in riverside bogs and fens for de novo populations. Potential habitat was identified using infrared aerial photography and was systematically surveyed at each site, with GPS data collected on the perimeters of all Narthecium patches found. Notable findings included the discovery of 33 de novo populations, increasing the number of known occurrences by 57% and the total areal coverage by 86%. Other populations that previous surveys had failed to find were rediscovered, and several extirpations were confirmed. Spatial analyses found the total area of N. americanum to be 32 ha, ranging from less than 1 m² to more than 4 ha per site. Populations were clustered along portions of 10 rivers, and a reassessment of occurrence delineations based on their spatial distribution resulted in a reduction to 18 extant and 10 historic/extirpated occurrences. Ninety-four percent of N. americanum by area occurred on publically owned lands, 96% within state and federal Pinelands boundaries, and 81% in the Pinelands Preservation Area. Present status and threats to the species, and the usefulness of remote sensing, geographic information systems, and systematic survey methods for rare plant monitoring and research are discussed.

In cryptically dioecious species, at least one morph is functionally unisexual despite hermaphroditic morphology. In such species, sterile reproductive structures may indirectly increase fitness of the cryptic morph. This study manipulates pollination mode to investigate two hypotheses regarding the influence of sterile stamens on female fitness in the cryptically dioecious Thalictrum macrostylum. Pollination mode and the presence of pollen limitation in natural populations were also investigated. In two natural populations, pollen receipt on pistils was quantified in open-pollinated and pollinator-exclusion flowers with varying numbers of stamens. Seed set was quantified in additional open-pollinated flowers, a subset of which received supplemental pollen to test for pollen limitation. Females were not significantly insect pollinated at either site. Number of sterile stamens per flower was positively related to pollen receipt in open-pollinated flowers at one site, but had no influence on seed set at either site. In one population, seed set was significantly pollen limited, and high variance in seed set among pollen-addition flowers in both populations indicates that high pollen loads do not always increase seed set. In the wind-pollinated and cryptically dioecious Thalictrum macrostylum, sterile stamens in females do not appear to increase female fitness. Other explanations for the persistence of stamens and sterile pollen in females of T. macrostylum should be sought.

Sprekelia formosissima (L.) Herbert is a bulbous ornamental species of the Amaryllidaceae family, distributed from northern Mexico to Guatemala. Different reports on cytogenetic research on this species show differences in chromosome numbers (2n = 60, 120, 150, 180) with a basic number of x = 30. Since the chromosome number of plants can provide useful information for various fields of research including karyotaxonomy, genetics, and cytogenetics, it is important to determine the chromosome number for this species. Bulbs of S. formosissima were collected in three different locations in the state of Jalisco, Mexico. Meristematic root cells were analyzed cytogenetically using a modified steam-drop method. The three populations showed different chromosome numbers and ploidy levels, 2n = 2x = 60, 2n = 4x = 120, and 2n = 5x = 150. The ploidy level was compared with morphological traits showing higher values related to higher ploidy levels. The populations analyzed correspond to new polyploid cytotypes of S. formosissima.

A new species, Croton uliginosus, from Midwestern Brazil is described and illustrated. It is related to Croton junceus Baill., from which it differs mainly in shape, margins and veins of leaf blade, position of acropetiolar glands, number of pistillate flowers in the rachis, presence of glands, shape of pistillate sepals, number of stamens, and length of fruiting pistillate calyx in relation to the fruits. The habitat, preliminary conservation assessment, periods of flowering and fruiting, and morphological relationships of the novel species with its closest species are also provided. Additionally, the geographical distribution map and color plates of the new species and C. junceus are provided. The latter is a species endemic to Midwestern Brazil but not yet revealed in photographs, whose taxonomy is still poorly known.