Invasion of deciduous forests by woody shrubs such as Lonicera maackii is known to negatively impact the abundance and richness of native herbs, but effects on recruitment of seedlings and saplings of native trees, such as Acer saccharum, are less well known. Ultimately, these impacts could alter the species composition of forest trees. Our study was designed to evaluate the impact of L. maackii and environmental factors on recruitment of A. saccharum seedlings and on the transition of seedlings to saplings and saplings to mature trees. We selected four study sites in southwestern Ohio where we censused L. maackii and A.. saccharum seedlings, saplings, and trees in 16 plots (eight with and eight without L. maackii) at each site. We measured L. maackii abundance and maximum diameter of the primary stem (an indication of shrub size), edaphic factors (soil density, pH, soil percentage of nitrogen [%N], soil percentage of carbon [%C]), topographic factors (elevation, slope, aspect), biotic factors (overall tree abundance), and human influences (proximity to roadways). Using a generalized linear mixed model with model comparison techniques, we found that in plots with larger L. maackii, seedling recruitment was lower, the transition from seedlings to saplings was greater, and the transition from saplings to trees was unaffected. Seedling recruitment increased with increasing soil %C, but decreased with increasing soil AN. Slope was positively associated with a greater transition from seedlings to saplings, and soil density and soil %C negatively affected the transition to trees. The transition to trees was higher with greater tree abundance, and the transition to saplings and trees was greater away from roadways. Overall, these results indicate that environmental factors have positive and negative impacts on recruitment of A. saccharum, and large L. maackii have both a negative and positive relationship to recruitment. Further studies will be necessary to uncover the mechanisms involved in the negative and positive relationships of L. maackii to recruitment of A. saccharum.

Core Ideas The onset of reforestation is a key factor controlling SOC and N stocks. Stocks increased from partial to full reforestation, particularly in shallow soils. SOC/N ratio increased with time since reforestation in deep but not shallow soils. Increased SOC/N ratio in deep soils reflected accumulated SOC but stable N. No relationship existed between SOC and N stocks and tree composition or structure. Reforestation and afforestation of agricultural land can lead to increased storage of C and N. Few studies have determined the effect of reforestation on N compared with C accumulation or the impact of forest community structure on soil organic C (SOC) and N stocks. We selected a chronosequence of six forested study sites to investigate whether SOC and N were affected by land‐use history or forest community structure. We took soil cores at depths of 15 to 35 cm from eight plots at each study site, measured SOC and N concentrations, SOC/N ratios, the minimum time since partial and full reforestation, and tree composition and structure. The SOC and N concentrations increased with time since partial and full reforestation in shallow soils (top 10 cm; p < 0.01) but less so in deeper soils (10–20 cm; p > 0.05; rocky soil limited analyses below 20 cm). The SOC and N concentrations were more closely linked to the onset of reforestation. The SOC/N ratio increased with time since partial and full reforestation in deeper soils ( p < 0.01) but not in shallow soils ( p > 0.05). There was no relationship between either SOC or N and forest composition or structure ( p > 0.05). Our results demonstrate that the onset of reforestation is a key factor controlling SOC and N concentrations, which increased from partial to full reforestation, particularly in shallow soils. The more pronounced increase in the SOC/N ratio in deeper soils reflected an accumulation of SOC with time in these soils, while N content remained comparatively stable.

Unprecedented population growth and urban expansion are rapidly transforming natural and agricultural settings into highly modified urban and suburban landscapes in developed areas worldwide. A myriad of anthropogenic environmental disturbances invariably accompany such dramatic shifts in land use, and disentangling the effects of these multiple stresses on ecosystem variation pose major challenges as the world’s urban population continues to increase. Here, we quantitatively characterized environmentally-mediated variation in tree-community composition along an Urban-Wildland gradient in southwestern Ohio, using tree censuses conducted in sample plots at six study sites categorized as Urban, Exurban, or Wildland based on analyses of a broad suite of natural and anthropogenic environmental variables. Several direct measures of the tree-census data, including species richness, abundance, diversity metrics, and evenness, exhibited significant increases from Urban to Wildland sites. Non-Metric Multidimensional Scaling (NMDS) showed that tree composition within study plots also varied systematically along the gradient, with significant differences among sites captured primarily on NMDS Axis 1. The dominant tree species at Urban and Exurban sites was Acer saccharum (sugar maple). While this species was also abundant at Wildland sites, two other species, Asimina triloba (paw paw) and Juniperus virginiana (red cedar) tended to be more abundant. Regression-tree analyses demonstrated that tree-community composition was controlled by a complex combination of natural and anthropogenic factors, with primary roles for population density and other indicators of urbanization at broader and intermediate scales; natural factors, such as aspect, soil drainage, elevation, slope, and soil pH were important in differentiating among Urban, Exurban, and Wildland sites already primarily categorized by anthropogenic agents.

Although many invasive plant species negatively impact native plants in natural communities, their relationships with other nonnative plants remain relatively unexplored. In some cases, invasive plant species may be capable of facilitating the invasion of other nonnative species into natural areas, thereby exacerbating their invasive ecosystem effects. We examined whether Lonicera maackii (Rupr.) Herder (Amur honeysuckle), a woody shrub from Asia that is rapidly spreading throughout the midwestem USA, is associated with other invasive plant species, compared to locations where L. maackii is not yet present. Lonicera. maackii is known to detrimentally impact native plant communities and to alter soil nutrients and light levels in invaded areas, indicating that it has the potential to act as an invasion facilitator. Using plots with and without L. maackii in four study sites across southwestern Ohio, we quantified species richness (S), relative abundance (RA), proportion of total species (PR), and diversity (H) of invasive species, compared to native and nonnative species that were not invasive. The presence of L. maackii was significantly associated with an increased number, proportion, and diversity of other invasive plant species, but the relative abundance of invasive individuals did not differ between plots with and without L. maackii. Presence of L. maackii and also distance to roads were explanatory variables that predicted S. PR, RA, and H for invasive species. Overall, the association of L. maackii with other invasive plant species in natural areas indicates the need for continued investigation into the potential role of L. maackii as an invasion facilitator in eastern deciduous forests in the midwestern USA.

Introduced plants threaten biodiversity and ecosystem processes, including carbon (C) and nitrogen (N) cycles, but little is known about the threshold at which such effects occur. We examined the impact of the invasive shrub Amur honeysuckle on soil organic carbon (SOC) and N density at study sites that varied in invasion history. In plots with and without honeysuckle, we measured honeysuckle abundance and size (basal area) and extracted soil cores. SOC and N densities were highest at the site with the longest invasion history and highest invasion intensity (i.e., greatest abundance and basal area of honeysuckle). Basal area of honeysuckle positively affected SOC and N densities likely because of increased litter decomposition and altered microbial communities. Because honeysuckle increases forest net primary productivity (NPP) and SOC, it also may play a role in C sequestration. Our results demonstrate the need to consider the influence of invasion history and intensity when evaluating the potential impact of invasive species.

We studied how degree of urbanization affected forest-floor herbs in deciduous forest along an urbanization gradient from west to east of Cincinnati, OH. We measured species diversity, richness, and abundance of herbs in 16 30 × 30 m plots at two Urban, two Exurban, and two Wildland sites. Because the invasive shrub Amur honeysuckle (Lonicera maackii) negatively affects richness and abundance of native herbs, half of these plots contained honeysuckle, except at the Wildland sites where honeysuckle was absent. We used General Linear Models or Generalized Linear Mixed Models to determine the effect of edaphic, geographic, forest composition, human effects, and honeysuckle variables on herbs and used model comparison techniques to identify those variables that significantly affected herbs. Human effects (e.g., proximity to roads) and geography (e.g., aspect, slope) were the most important factors affecting herb richness and abundance, and geography (e.g., elevation) was the most important factor affecting herb diversity. Honeysuckle (measured as diameter of primary stem) had no effect on diversity or richness of herbs, but positively affected herb abundance. Herb diversity did not vary significantly along the urbanization gradient, but higher herb richness and abundance in Exurban and Wildland sites along the urbanization gradient were associated with higher tree diversity, richness, and abundance, shallower slopes, greater distance to roads, and smaller honeysuckle shrubs.

Northern Appalachian Basin deposits and associated fossils have served as exemplars for ecological-evolutionary investigations, and as the reference interval for the concept of coordinated stasis. Here, we examine faunal and environmental changes within the uppermost Hamilton and lowermost Genesee Groups of the late Middle Devonian succession of New York State. Dramatic diversity loss, faunal migrations, and ecological restructuring recognized in these strata have been used previously to define the end of the Hamilton ecological-evolutionary subunit, and, furthermore, these strata and corresponding faunal changes represent the type region for the global Taghanic Biocrisis. We present and analyze a new, high-resolution data set of post-Taghanic Genesee fossil assemblages, in which we recognize 11 biofacies corresponding to an onshore-offshore (depth) gradient. The Genesee Fauna shows an unexpectedly high taxonomic similarity to nearshore biofacies of the pre-Taghanic Hamilton Fauna, related to the persistence of siliciclastic-dominated nearshore settings through the Taghanic Biocrisis, whereas the onset of anoxic/dysoxic conditions typified offshore portions of the environmental gradient. The "Nearshore Refugium Model" of Erwin offers a possible explanation for the persistence of taxa through the biocrisis in nearshore settings. This constriction was followed by subsequent expansion of these residual taxa to offshore environments in relatively similar associations, as increased Acadian orogenic activity and resultant delta progradation increased habitable space offshore by decreasing the extent of deeper-water, oxygen-poor settings. Although taxonomic similarity was high between the Hamilton and Genesee Faunas, biofacies structure differed primarily because of tectonically driven physical transformations to the basin and associated biotic turnover. Nevertheless, the combination of high taxonomic persistence of Hamilton nearshore taxa and the introduction of relatively few new taxa in the Genesee Fauna resulted in a taxonomic holdover that was much higher than observed in the original formulation of coordinated stasis.

Actualistic studies of shell taphonomy in the marine subfossil record have found alteration in shell color to be a highly useful taphonomic indicator; however, the viability of shell discoloration for this purpose in the more profoundly altered material of the deep-time fossil record has not been explored. We investigated the relationship between the shell discoloration of Ordovician brachiopods and their taphonomic state to determine what information discoloration could provide about the conditions under which the shells were preserved. We examined 1033 specimens of Vinlandostrophia and Hebertella from type-Cincinnatian outcrops in southwestern Ohio and northern Kentucky, using a sampling design that allowed us to test the taphonomic significance of shell color in multiple stratigraphic units and across a wide geographic area. For each specimen, taphonomic data were recorded and multivariate analyses of the taphonomic attributes performed. Our results demonstrate that fossil shell discoloration is strongly related to overall taphonomic state, with darker colors associated with evidence of shell degradation. Further analyses suggest that shell color may be related to the incorporation of sulfide minerals and organic matter. Darker colors may reflect a higher residence time in the taphonomically active zone, in environments with slow sedimentation rates or multiple burial and exhumation cycles. Alternatively, darker colors may be indicative of environments with higher probabilities of discoloration, related to sediment and pore-water geochemistry. The slicing correlation between shell discoloration and other indicators of taphonomic damage is evidence that discoloration reflects a taphonomic pathway from pristine to degraded shells, and may be a useful addition to taphofacies models.

Although morphological variation is known to influence the evolutionary fates of species, the relationship between morphological variation and survivorship in the face of extinction-inducing perturbations is poorly understood. Here, we investigate this relationship for veneroid bivalves in association with the Plio-Pleistocene extinction in Florida. Fourteen pairs of related species were selected for analysis, with each pair including one species that survived the Plio-Pleistocene extinction and another that became extinct during the interval. Morphological landmark data were acquired for more than 1500 museum specimens, representing 19 localities that encompass four well-known Plio-Pleistocene units in the study region. Procrustes superimposition was applied to each sample, and overall multivariate variation was calculated as the mean squared partial Procrustes distance between specimens and their mean form. Morphological variation was calculated at three geographic scales for each species, and differences in variation between survivors and victims were examined within each species pair. Results indicate that species surviving the Plio-Pleistocene extinction were significantly more variable morphologically than victims. Greater morphological variation may promote survivorship by directly enhancing species adaptations to changing conditions or by permitting the occupation of a larger geographic range. Alternatively, high morphological variation and survivorship may both be mediated by a third variable, such as large geographic range.