Understanding the patterns of past disturbance allows further insight into the complex composition, structure, and function of current and future forests, which is increasingly important in a world where disturbance characteristics are changing. Our objectives were to define disturbance causes, rates (percent disturbance per decade), magnitudes and frequency (time since last disturbance) for both secondary and old-growth mixed-oak stands, and to determine if all mixed oak stands experience similar disturbance history. The study was located in two southern Appalachian forests in western North Carolina, USA: Coweeta Hydrologic Laboratory, a 2,185 ha experimental forest with some history of harvesting, and the Joyce Kilmer Wilderness, a 6,805 ha old-growth forest with no known harvesting. We used dendroecological techniques to evaluate the disturbance histories and create chronologies of these mixed-oak forests. Average decadal disturbance rates ranged from 4.3% to 13.8%, similar to rates common in eastern temperate forests (5% to 20%). The decades of peak recruitment common to several stands were the 1840s, which coincides with the historical accounts of a hurricane; the 1900s through the 1940s, which coincide with logging and elimination of Castanea dentata (Marshall) Borkh. by chestnut blight; and the 1960s, which coincides with drought and an elm spanworm infestation. The large peaks of disturbance were often synchronous and widespread, affecting stands across both Coweeta and Joyce Kilmer. However, there were also scattered pulses of disturbance unique to single stands, suggesting that localized events also played a role in the disturbance dynamics. Periods of constant low rates of disturbance present in all stands also indicate the importance of small canopy gaps in these forests. We found that stands similar in disturbance regimes were also similar in species composition. Results from our study provide information on how past disturbances, both regional and local events, have shaped the current forest. This understanding could help inform models to better predict how forests might respond to future climate (e.g., rising temperatures and increasing precipitation variability) and disturbance patterns (e.g., more frequent and severe events).

Garlic mustard, Alliaria petiolata (M. Bieb.) Cavara & Grande, a European biennial, has become common in many Midwestern and eastern North American forests. Researchers have sometimes documented a two-year (two-point) population cycle in which the vegetative and reproductive phases alternate in abundance. However, little research has been conducted on the scale dependence of the two-point cycle and the extent to which the cycle is dependent on the density of A. petiolata. In addition to this interest in A. petiolata's population dynamics, researchers have investigated A. petiolata's effects on other plant species, often concluding that it displaces native herbs and inhibits tree seedling growth and survival through the production of allelochemicals. In order to examine both the population dynamics of A. petiolata and its possible effects on North American native plants, we conducted a four year study in which we monitored A. petiolata in a 6.2 ha portion of a Minnesota oak (Quercus) woodland at two spatial scales (0.5 m², 400 m²). We also conducted an indoor seedling pot study to investigate whether any soil inhibitory effects associated with A. petiolata may be exacerbated under drought conditions. We found that a two-point cycle was not sustained during the four year study throughout the entire study site. However, the two-point cycle was exhibited in high A. petiolata density areas in the study site, providing support for the hypothesis that the cycle is driven by competition between first-year (rosette) and second-year (stem) plants. Both the monitoring study and the pot experiment yielded little evidence that A. petiolata is a major agent of ecological change in the woodland. Rather, the data indicate that over the four years of this study A. petiolata and the other plant species in the woodland we studied are changing in abundance largely independent of one another.

As exotic species invasions continue to transform patterns of biological diversity, it becomes increasingly urgent to understand invasions' full consequences. Woody exotics that colonize closed-canopy forests have the potential for strong effects on plant communities. Berberis thunbergii DC, one such species, has invaded forests throughout eastern North America. Here we quantified the impacts of B. thunbergii invasions on the diversity and composition of native plant communities, both directly and through possible modifications of nutrient, moisture, and light availability. Plots with and without B. thunbergii had similar species richness, evenness, and diversity. Only two species were less likely to occur in plots with B. thunbergii. We also found no effect of B. thunbergii on soil moisture or other key soil properties such as pH and organic matter content. Plots with B. thunbergii had lower light levels at 10 cm from the ground, as under any shrub. It is possible that the invasion we observed may develop into a dense thicket with more severe impacts; however, the effects of B. thunbergii were modest at this time.

Droughts are expected to increase in frequency and severity in many regions as climate changes. The impact drought has on tree growth may depend on the timing of drought. The historical climate-growth response of trees provides insight into how a species may respond to future changes in climate and also enables us to understand how drought and the timing of drought has impacted growth. In this study, we use dendrochronology to examine the climate and drought response of Quercus myrtifolia Willd. growth on sites from three different scrub ridge systems in central Florida. Five site chronologies and a regional chronology were created from tree-ring measurements. Growth of Q. myrtifolia correlated positively with spring precipitation and the standardized precipitation index (SPI). March, April, May, and June SPI explained 21.5 to 58.3% of the variance in growth of Q. myrtifolia. The growth response of Q. myrtifolia to spring SPI was similar between sites, with the exception of Malabar West, where Q. myrtifolia occurred on poorly-drained soils. Seasonal droughts explained more of the variation in Q. myrtifolia growth than annual droughts. Spring droughts significantly decreased Q. myrtifolia growth at all sites, and summer droughts significantly reduced growth during the subsequent year at one site. Our data suggest that spring drought is the climatic limiting factor for Q. myrtifolia growth.

In recent years, the eastern United States has experienced little tree mortality due to insects; nonetheless, the emerald ash borer threatens future composition of the ash genus, which is distributed in the eastern and central United States. Given probable decline of the ash genus due to the emerald ash borer, I assessed recent range dynamics of F. pennsylvanica Marsh. (green ash), F. americana L. (white ash), F. nigra Marsh. (black ash), and Populus deltoides Bartr. ex. Marsh. (eastern cottonwood), one of the species that has been replaced by F. pennsylvanica. I compared current and oldest available USDA Forest Service Forest Inventory and Analysis surveys. Fraxinus pennsylvanica expanded 32 million ha in range (≥ 0.5% of total species composition, or total number of stems) during approximately a mean difference of 29 years. Moreover, F. pennsylvanica increased 6 million ha where it was present at ≥ 10% of total species composition. Fraxinus americana increased 15 million ha in range but decreased 7.5 million ha where it was present at ≥ 10% of composition. Fraxinus nigra remained stable in range and generally increased in composition. Similarly to F. americana, P. deltoides increased in range 16 million ha but decreased 11 million ha where it was present at ≥ 10% of composition. There were no indications of mortality due to emerald ash borer. Throughout most of their ranges, ashes were a minor species within diverse and dense forests of the eastern United States. The greatest impacts of emerald ash borer should occur in the central United States, where F. pennsylvanica was a major species of riparian woodlands and provides structure to dependent wildlife and plants and where emerald ash borer recently has been discovered.

Edaphic factors play an important role in determining moss species distribution and establishment, yet relatively few studies of the soil environment of mosses have focused on disturbed soil habitats such as those found next to road edges. Plot ground cover, soil physical, and soil chemical measurements were analyzed for 288 0.5 m² plots at two distance groupings (near: 0.5 and 2 m and far: 5 and 8 m) from 24 roadside locations across northern New York, central New Hampshire, and central Vermont. Forty-eight species of moss were encountered on 164 of the 288 sample plots with a mean species richness of 2.5 species per plot. Four groups of mosses that act in coordinated ways were established, defined primarily by soil pH, calcium, magnesium, manganese, and aluminum. Within these four groups, species also exhibited a clear distribution preference towards either near or far roadside plots that is loosely based on growth form. Our finding of a group of moss species that are frequently present in the difficult growing environment found in close proximity to roadsides suggests that future studies in moss ecology and physiology could lead to useful insights in plant adaptations to extreme environments, including tolerance of heavy metals, reduced mineral nutrients, and desiccation.

Rhipsalis, the largest genus of tribe Rhipsalideae (Cactaceae), comprises 37 characteristically epiphytic species and a few rupicolous ones. It is well represented in the Brazilian flora, and its center of diversity is in wet tropical and subtropical forests of southeastern Brazil. Rhipsalis dissimilis (G.A. Lindberg) forma epiphyllanthoides and R. floccosa (L.) subspecies pulvinigera are sister species with very distinct habits within the genus. This study analyzes and compares the morphoanatomy of these species aiming to verify which modifications found in the former may be related to its (rupicolous) terrestrial habit. We collected 23 individuals of R. dissimilis in an area of rocky outcrops in Ponta Grossa, State of Parana, and 23 individuals of R. floccosa in a remnant of Atlantic Forest formation in Curitiba, State of Parana. Length, diameter, area, volume, dry and fresh mass, water content, and stomatal and areolar density in the median portion of the stems of both species were measured. Histological slides were mounted to assess tissue thickness and percentage of lignified tissues. Both species present features typical of Cactaceae. Regarding habit differences, R. floccosa subspecies pulvinigera shows significant reductions of some tissues such as absence of ribs and diminished succulence, which constitute selected adaptations to epiphytism. Rhipsalis dissimilis forma epiphyllanthoides presents increased succulence, a lower height/diameter ratio, and ribs, among others. Such features are in line with those observed in other lineages of terrestrial cacti. Considering that Rhipsalis ancestral habitat was epiphytic, R. dissimilis may have retained a more plesiomorphic form suitable for colonizing a terrestrial habitat.

A previously annotated checklist of liverworts, totaling 65 species from the Delmarva Peninsula, was reported in the Journal of the Torrey Botanical Society in 2011. This new publication adds another taxon Riccia sorocarpa Bisch., to the hepaticae list of the region and from the State of Maryland.