Many communities invaded by one non-native plant species also are invaded by others due to a shared response to environmental factors that promote invasive species generally, such as fragmentation, disturbance, and proximity to seed sources. Direct comparison of these co-invasive species in their shared communities therefore is necessary for understanding the ecology of invaded communities, particularly if management resources must be prioritized. We compared ecological characteristics of two of the most important co-invasive herb layer species in forests of the eastern United States, Alliaria petiolata (garlic mustard, a C₃ biennial herb native to Europe) and Microstegium vimineum (Japanese stilt-grass, a C₄ annual grass native to east Asia). Both are invasive across a wide geographic range, establish dense stands under varying canopy covers, and are associated with lower native herb layer diversity and abundance. However, A. petiolata has attracted much greater attention from the scientific and management communities. Our research had three related components aimed at understanding which species may be a greater threat. We conducted a greenhouse experiment with shaded and unshaded growing conditions, in which M. vimineum grew much greater shoot biomass (although total biomass was similar) and photosynthesis rates for M. vimineum generally exceeded those for A. petiolata. We also did a large field experiment using transplants grown from seed. Microstegium vimineum had greater survivorship, less insect herbivory, larger mass, and higher photosynthesis rates than first-year A. petiolata. In addition, we studied a co-invaded natural community. Both species' percent cover were variable across the site but had no relationship to photosynthetically active radiation (PAR) levels. Microstegium vimineum had higher cover in 2001 and by 2005 had increased dramatically over A. petiolata in co-invaded plots. In the summer months M. vimineum had greater photosynthesis rates (measured in situ with a Li-Cor 6400) and were matched only by A. petiolata's early spring rates. These results indicate that in forests where they co-invade M. vimineum may have greater potential for spread than A. petiolata and deserves increased attention from both scientists and forest managers.

Alliaria petiolata is an invasive herb impacting forests throughout the eastern United States. We studied the impacts of glyphosate, bare ground, and summer precipitation on A. petiolata cover and density in two forest stands of different ages at Hueston Woods State Park, Preble and Butler Cos., OH. Fifty 1 × 1 m plots were established in each stand and 25 plots per stand were treated with glyphosate each November 2000–2004. Cover and density of A. petiolata rosettes and adults were measured multiple times each year from 2000 through 2005. Percent bare ground was estimated using a point frame in May 2003.

Adult cover in May was significantly lower in sprayed vs. unsprayed plots in three of five years; in the other two years adult cover was very low in both sprayed and unsprayed plots. However, spray treatment did not significantly affect May rosette cover across years. ANCOVA revealed that May 2003 bare ground positively associated with density of A. petiolata rosettes in May 2003, but bare ground was not significantly associated with October 2003 rosette density. Variation across years in both October rosette density and May adult density of A. petiolata was significantly associated with precipitation the previous June; wetter Junes were followed by higher densities.

Despite sustained suppression of adult A. petiolata in plots sprayed with glyphosate, new rosettes appeared each spring at densities comparable to unsprayed plots, which we attribute to seed dispersal from outside of the plots. Bare ground had minimal effect on A. petiolata populations. Evidence that A. petiolata density was positively affected by June precipitation suggests that management efforts should be focused in years of wet summers.

Ailanthus altissima tree seedlings were excavated from each of two habitats: (1) a forest adjacent to a trail and stream and (2) a non-forested steep, barren slope adjacent to a major highway. Each seedling root system was examined for colonization by mycorrhizal structures using light microscopy and transmission electron microscopy. The roots were colonized by one or more endomycorrhizal fungi with Arum-type colonization. Endomycorrhizal colonization of the seedlings from the non-forested site (65.2%) was significantly greater than that of the seedlings from the forested site (37.9%). Colonization by intercellular hyphae and vesicles was significantly greater in the non-forested habitat than the forested habitat. This exotic invasive species may benefit from the rapid colonization of endomycorrhizae in more extreme open environments.

At the landscape scale, herbaceous understory plant species are limited in return to forested settings by dispersal. At fine-scales, microhabitat characteristics are known to be important in determining the distribution of herbaceous understory plant species. Fine-scale manipulative experiments to determine responses of understory species to disturbance, however, are few and limited to Europe and the Pacific northwest. The Unified Neutral Theory of Biodiversity (UNT) predicts that species enter disturbed habitat in abundances proportional to their neighboring abundance. I assessed the reestablishment of dominant understory plant species (Dryopteris intermedia, Lycopodium lucidulum, and Oxalis acetosella) following small-scale disturbance in a Catskill northern hardwood forest. While reestablishment of all species was significantly and positively correlated with the presence of each species in surrounding areas indicating the importance of dispersal limitation of reestablishment, rates of recovery were species specific. Reestablishment of O. acetosella was far greater than that of the other species. In fact, no sexual reproduction was observed for D. intermedia and L. lucidulum. Cover of D. intermedia and L. lucidulum was significantly and positively correlated with pre-disturbance cover but this was not true for O. acetosella, indicating that for the pteridiophytes, habitat quality (as well as dispersal) was an important factor in reestablishment. Reestablishment therefore was influenced by dispersal and habitat characteristics, was species specific, and did not follow the predictions of the UNT. Thus, small-scale disturbance can have an important effect on the composition of the herbaceous community in northern hardwood forests.

Demography, growth, and flowering of Dionaea muscipula (Venus' fly trap) were studied during three years (2003–2005) following prescribed fire. Data were collected in permanent quadrats where the developing vegetation was either repeatedly clipped or allowed to grow. Clipping increased light availability at the soil surface. Over the study period, seedling establishment and flowering declined with increasing time since the last prescribed burn. Seedling densities did not differ between clipped and control quadrats, although greater numbers of seedlings grew to adult size in control quadrats and this significantly influenced population size-class structure. Clipping had no effect on leaf number or senescence, but plants in control plots were larger and had marginally longer petioles. The plant populations initially mapped in 2003 showed a continuous decline throughout the study and this decline was punctuated by temporary senescence linked to drought conditions. Drought-induced senescence had a persistent influence on plant size. Relatively higher seedling recruitment to the adult population in control quadrats produced an overall population increase of 18% as compared to a 17% decline in the population from clipped quadrats. Dionaea muscipula may have limited ability to respond to increased light availability due to leaf development constraints and repeated drought-induced senescence. Fire-dependence may best be defined in terms of seedling establishment and stimulation of flowering. Consistent soil moisture is critical to Dionaea muscipula but the species has characteristics that allow persistence across a wide range of vegetation trajectories.

Understanding the processes contributing to long-term change in remnant plant communities is relevant to community ecology and conservation biology. Using a unique set of historical field data, we undertook a natural field experiment to examine how novel landscape conditions, fire history, and increased woody canopy affect plant composition and structure of tallgrass-prairie remnants in Wisconsin, USA. In 1999 we used 1-m² quadrats to resample 21 remnant tallgrass-prairie sites that had been similarly sampled between 1947 and 1954. Results reveal that community change was largely recruitment driven, with mean recruitment (41.4 spp./site ± 14.4 SD) significantly different from mean extirpation (28.4 spp./site ± 11.5 SD). Species density increased significantly from 10.6 ± 2.3 to 12.8 ± 3.9 spp./m², indicating that regional processes contribute substantially to species diversity. We propose that increased species density is the inevitable consequence of prairie's historical condition of seed limitation combined with modern seed subsidy from an altered landscape now rich in habitat generalist species. We hypothesized that species responses to fire suppression and increased shading would vary with their competitive versus reproductive ability. The bulk of increaser species were habitat generalists. Declines among habitat specialists and once-dominant species were exacerbated by fire suppression. Canopy effects were generally weaker than fire suppression effects, consistent with the theory of strong floristic similarity of prairie and savanna vegetation. Extirpations of rare species (i.e., original quadrat frequency ≤ 5%) ranged from 48 to 84 percent, but extirpations were independent of fire regime or woody canopy. Our results suggest that the instability of remnant communities is the consequence of regional, local, and stochastic processes.

Serpentine grasslands support a unique endemic flora composed of many rare species that are tolerant of the inhospitable soil conditions characteristic of ultramafic soils. In the eastern United States, rare plants of many serpentine grasslands are being displaced as a result of invasion by Pinus species and consequent changes in environmental conditions. Community structure and function of symbiotic soil arbuscular mycorrhizal fungi (AMF) also may be affected by Pinus succession. This study examined changes in soil properties, AMF communities, and plant growth in serpentine grassland soils that have been invaded by Virginia pine (Pinus virginiana Mill.). Sites representing three vegetation types (grassland, pine savanna, and pine woodland) were assessed at the Soldiers Delight Natural Environmental Area, Maryland, USA. In comparison to grassland sites, soil pH and concentrations of Ca, Mg, and Ni were reduced in pine woodland soils. Savanna soils exhibited an increase in Mg and Ni concentrations relative to grasslands. In greenhouse experiments, Mg toxicity imposed the largest limitation to plant growth on these serpentine soils, expressed most dramatically in savanna soils, where Mg concentrations were as high as 1,575 µg g⁻¹ soil. Plant growth was least constrained on soil from pine woodlands. Pot cultures from grassland soils yielded the greatest AMF species richness and sporulation. Richness and sporulation were reduced in savanna and pine woodland soils, although pine invasion did not alter fungal diversity indices. The negative impact that pines had in the early stages of succession on fungal abundance and plant growth, along with the decreased serpentine signal seen in woodland soils, have important implications for the restoration and management of plant species diversity on these serpentine sites. Altered soil chemistry and depleted AMF populations may be factors that function to limit the success of herbaceous vegetation adapted to serpentine soils.

By the middle of the 19^th century, nearly all of central Massachusetts, USA, was cut at least once and 80% deforested. When did deforestation begin? We recorded all the trees and other corner markers used in 18^th century proprietors' surveys of Shrewsbury, MA. From 1718–1799, the percentage of corner markers that were “trees” declined from 45% to 20%, and the relative abundance of white oak tended to decrease. Unexpectedly, the relative abundance of white pine more than doubled. Overall, deforestation and alteration of species composition were already occurring in the 18^th century due to changing conditions, selective harvest, and differences in the resilience of the dominant trees. Proprietors' records can provide data on forest change as well as forest composition.

Pocosins are shrub wetlands of the southeastern coastal plain maintained by fire. Increased herbaceous plant diversity has been reported after wildfire. To test the effect of radiant heating on the seed bank of pocosin-upland ecotones, wet heat treatments were applied to Sphagnum substrate from a Virginia small depression pocosin. The seedling emergence method was used to quantify wetland seedling abundance and richness. Extant vegetation was measured at each seed bank sampling area and the seed bank and vegetation were compared with Sorenson similarity values. No significant seedling abundance, richness, or evenness effects were detected among wet heat and control groups. However, the high wet heat treatment (75 °C) significantly reduced the density of Sphagnum cuspidatum capitula more than 80% relative to the control. Mean seed bank density was 6,209 seedlings/m² (richness  =  11) and was dominated by Scirpus cyperinus (97.8%), contained many early successional species. The seed bank did not closely resemble the extant vegetation. Pocosin canopy was sparse and dominated by Pinus serotina. The shrub-sapling stratum indicated co-dominance of Acer rubrum and ericaceous species, potentially indicating a shift from a shrub bog to a wet pine-hardwood community.

Naumann, J. C. and D. R. Young (Department of Biology, Virginia Commonwealth University, Richmond, VA 23284). Relationship between community structure and seed bank to describe successional dynamics of an Atlantic Coast maritime forest. J. Torrey Bot. Soc. 134: 89–98. 2007.—Relationships between current community composition and the soil seed bank were investigated within a maritime forest on Virginia's Eastern Shore. Forty families, 48 genera, and 52 species were documented in the current community. Three overstory species (Liquidambar styraciflua, Acer rubrum, and Pinus taeda) were dominants and comprised 72% of all overstory trees sampled. Analysis of stem size classes indicated that P. taeda was not recruiting and would eventually be replaced by hardwoods. Ilex opaca, Toxicodendron radicans, and Lonicera japonica comprised the majority of cover in the understory. The forest was in a mid-successional seral stage. In comparison, 31 families, 43 genera, and 45 species were identified from the seed bank. Seed bank composition was largely distinct from the aboveground community, although seven tree species that emerged from the seed bank were present in the overstory. Dissimilarity between the present community and seed bank indicated that replacement of existing species is likely to occur from future seed rain, especially from bird-dispersal. Presence of invasive species within the overstory, understory, and seed bank may alter forest succession.

We surveyed freshwater and oligohaline portions of tidal river systems in Delaware, the eastern shore of Maryland, and southern New Jersey for native and introduced Phragmites australis populations. Populations of native P. australis occur along the major rivers of the eastern shore of Maryland, particularly the Choptank and Nanticoke Rivers, and were common along river and creek edges and typically less dense than introduced P. australis. In contrast, few native populations occur along rivers in Delaware and southern New Jersey where introduced P. australis dominates. These differences in distribution of native P. australis could be due to the magnitude of human impacts and the timing of invasion of introduced P. australis into these systems. The presence of so many populations of native P. australis on the eastern shore of Maryland is unique today as the subspecies has all but disappeared from much of its historical range along the Atlantic Coast.

We investigated distinctive aspects of the floristic communities associated with bamboo dominance (Guadua sarcocarpa and Guadua weberbaueri) in terra-firma forests of the Tambopata River watershed, southeastern Peru. Data were collected at five sets of paired plots (five bamboo-dominated, five tree-dominated) in which no evidence of prior human disturbance was identified. Three components of the plant community were analyzed: (1) trees (≥ 5 cm diam), (2) tree saplings (< 5 cm diam), and (3) large understory plants (shrubs and herbs ≥ 1.5 meters). We used three statistical techniques (DCA, TWINSPAN, and ANOVA) to identify distinct assemblages of genera associated with the presence/absence of bamboo, and/or other factors (e.g., soil drainage, geographic location). All three statistical techniques produced similar results: the presence of bamboo is associated with a distinctive floristic community of trees and understory plants, but the tree sapling component of the plant communities was not distinct. Species richness in bamboo-dominated stands, as compared with tree-dominated stands, was 60% lower for trees and 36% lower for understory plants, but not significantly different for tree saplings. Bamboo-associated canopy trees and understory plants were characterized by fast growth rates, tolerance of poorly drained soils, and capacity for vegetative re-sprouting in response to physical damage to stems. These results suggest that differences in both soil and disturbance regimes drive floristic differences between bamboo-dominated stands and adjacent stands without bamboo.

The discovery of three populations of the large-headed sedge, Carex macrocephala, in New Jersey described in this paper, represents the first report of this species from Eastern North America. Carex macrocephala grows at much lower densities in New Jersey than does the closely related Asiatic sand sedge, Carex kobomugi. We thus expected invasion by C. macrocephala to have less impact of on the abundance and diversity of native dune plants than have been seen in previous studies of the closely related invasive sedge, C. kobomugi. This expectation was largely supported: the presence of C. macrocephala in New Jersey's coastal dunes had no significant impact on the abundance of co-occurring plant species. Indeed, species richness and diversity were actually significantly higher in areas occupied by C. macrocephala than in surrounding areas. New Jersey appears to be one of the few places in the world where C. macrocephala grows in close proximity to C. kobomugi, suggesting the possibility of hybridization between these species in the future. Since hybrids have the potential to be more invasive than their parent species, this has serious management repercussions.

The structure and ultrastructure of immature to fully mature glandular dots in the leaf, floral organs and fruit, and their secretion components were described in Caesalpinia echinata Lam. (Leguminosae) for the first time. Data showed that glandular dots were groups of idioblasts with contents that reacted positively for both lipophilic and hydrophilic substances. Idioblasts originated from successive divisions of the ground meristem cells or mesophyll cells of an ovary of a fertilized flower. Following division, cells enlarged, the cytoplasm became denser and its content became full. No idioblasts were observed after fruit sclerification. Besides these mixed-content idioblasts, some cells in the sepals, petals and mesocarp were found to contain phenolic compounds, which probably represent a kind of constitutive defense mechanism, once the flowers and fruits become highly fitness-valued parts of the plant and can be commonly attacked. The contents of the idioblasts are released as the growth rate of the embryo increases, indicating that the plant probably diverts the precursors of secondary metabolites into the primary metabolism, at this critical time of embryo development.