Exclosure studies have illustrated the profound effects overabundant populations of white-tailed deer can have on forest plant communities. However, complete exclusion of deer creates an artificial condition in most forests, and examining the long-term response of plant species composition and diversity to exclusion can provide valuable insight into the historic role of deer herbivory in forests. In 2014, we resampled spring flora and woody regeneration in a series of exclosure and control plots established in Great Smoky Mountains National Park in 1996. By comparing our data to regeneration data from 2002 and spring flora data from 2004, we were able to examine differences in vegetation at 6–8 and 18 yrs after deer exclusion. We observed a significant (P < 0.001) increase in the density of woody stems between 2002 and 2014 across all sites, with significantly more stems found within exclosures (P < 0.001). This increase in woody stem abundance within exclosures was associated with a decline in the abundance of some small-stature, spring herbaceous species. However, large-stature (taller) herbs, when present, tended to increase in abundance between sampling periods. Nonmetric multidimensional scaling ordinations supported this relationship between woody regeneration and herbaceous species composition. Shifts observed in spring flora composition along dominant ordination axes were correlated with the density of woody regeneration. Although our study further illustrates the negative effects of overabundant deer populations on plant communities, it also highlights the context-dependent nature of these effects and the potential consequences of long-term exclusion of herbivory on compositional diversity.

Plant tolerance to herbivory is an important component of plant competitive ability, which can facilitate the plant invasion process. The prediction of higher tolerance to herbivory in invasive plants has received mixed support in experimental studies, partially because of differences in methods of estimating plant tolerance in terms of plant growth. Using nondestructive methods to accurately estimate aboveground biomass, a standard measure of plant growth, can be challenging, especially for grasses. In addition, using different proxies for plant biomass may potentially cause mixed results in the estimation of plant tolerance. To address these issues, in our study, we conducted field and greenhouse experiments using native Andropogon gerardii Vitman and Bouteloua curtipendula (Michx.) Torr. and exotic Bothriochloa ischaemum (L.) Keng and Miscanthus sinensis Andersson grasses and examined their relative response to nymphal Melanoplus spp. grasshoppers. We first determined that, in most grass species, the product (Plant height × Number of leaves) was the best predictor of changes in plant biomass during 3 wk of plant growth. Based on this best predictor in grasshopper herbivory assays, we then found no difference in tolerance to herbivory among our study grasses. These results suggest that exotic grasses, which have not yet become invasive at the study sites might not demonstrate strong allocation from defenses to growth and reproduction, at least at the current time in these locations.

The nonrandom distribution of insect herbivory among plants is generally thought to reflect variation in plant-defense strategies and/or insect preferences for particular plant genotypes, where less-defended plants suffer the most damage. However, we postulated that aggregated distributions of herbivory may occur when (a) plants support greater herbivore densities under conditions with better resources (plant's choice), (b) plants with more nutrient-rich leaves are preferred more by herbivores (herbivore's choice), or (c) both, where plants living in better conditions can support more herbivores and have higher-quality leaves that herbivores also prefer. We tested these hypotheses using a population of black tupelo, Nyssa sylvatica Marshall (Cornales: Nyssaceae) and the tupelo leafminer, Antispila nysaefoliella Clemens (Lepidoptera: Heliozelidae). We found that the among-tree variation in herbivore density was positively associated with nutrient-cycling rate and not with leaf-nitrogen content, which supports the plant's choice hypothesis. Our results suggest that environmental conditions may have a more important role than host plant quality per se in determining the distribution of herbivores among trees.

The middle-Holocene decline of Tsuga canadensis (L.) Carrière (eastern hemlock) across eastern North America has been attributed to various causes, including the widespread outbreak of an insect pest, such as Lambdina fiscellaria (hemlock looper). We tested this hypothesis by searching for insect remains in sediment cores from Hemlock Hollow, a small basin in north-central Massachusetts. Previous analyses of this site demonstrated that it has been surrounded by Tsuga forest for the past 10,000 yr. We found the remains of chironomids and beetles in the cores but not in sediments dating to the interval of low Tsuga abundance; remains of Lambdina fiscellaria were not encountered. These results are consistent with the interpretation that the decline of Tsuga at Hemlock Hollow was not caused solely by an insect outbreak. The presence of Lambdina fiscellaria remains in middle-Holocene sediments at other sites in the region may reflect local outbreaks, perhaps facilitated by drought or other changes in climate that stressed Tsuga populations.

On October 29, 2012, Superstorm Sandy crashed into the New York Bight as a post-tropical cyclone. This storm produced extensive damage to the New Jersey and New York coastal zone. Much of the damage was caused by the storm surge that accompanied Sandy and the shifting of sand and destruction of coastal dunes. Our study was concerned with the effects that this event had on the vascular flora of the salt marshes in the impact zone. We visited six New Jersey-New York marshes in the late summer and early fall of 2013 and compared, using parsimony analysis, the current state of the vascular flora of those marshes against a pre-Sandy database. Although we observed relatively minor variations in the vascular flora at these sites, that is, the loss of some species and gains in others, overall, most plant species post-Sandy was the same as those pre-Sandy. Thus, we conclude that the species composition of the vascular flora of these salt marshes showed a remarkable degree of stability in the face of this catastrophic disturbance.

We investigated the hypotheses that (a) differences in metal uptake exist between dandelion (Taraxacum officinale Weber; Asteraceae) clones sampled from unpolluted and polluted sites when grown in polluted media, and (b) differences in metal uptake into dandelion roots versus leaves exist for clones sampled from unpolluted and polluted sites when grown in polluted media. These hypotheses were tested by performing a series of reciprocal, greenhouse-planting experiments in which distinct dandelion clones (12 clones, identified by DNA fingerprinting, from each site type) sampled from two unpolluted and two polluted (relatively high copper [Cu], lead [Pb], and zinc [Zn] soil concentrations) sites were grown pairwise in both unpolluted (nutrient solution only) and polluted (nutrient solution 120 mg kg⁻¹ Cu, 700 mg kg⁻¹ Pb, and 260 mg kg⁻¹ Zn) media (N = 48 pairwise plantings for each medium type). Analyzing the entire data set (including unpolluted and polluted treatments), dandelion clones sampled from polluted sites were shown to take up significantly greater quantities of Cu, Pb, and Zn, on both a concentration (root vs. leaves in milligrams per kilogram) and total plant (average unpolluted vs. polluted in micrograms) basis, than did clones sampled from unpolluted sites (ANOVA, P ≤ 0.05). When grown in polluted media, clones from polluted sites, on average, accumulated 4.2 times as much total Cu, 17.76 times as much total Pb, and 4.2 times as much total Zn in their tissues as clones sampled from unpolluted sites. Overall, dandelion clones sequestered significantly more Cu, Pb, and Zn in their root tissues than in their leaf tissues (ANOVA, P ≤ 0.05), regardless of the site type from which they were sampled. These results reveal that dandelions are Cu, Pb, and Zn accumulators and that differences in metal-uptake capabilities exist among North American clonal genotypes. Results indicate that dandelions, and perhaps other plant species, being screened for phytoremediation purposes should be collected from metal-polluted locales.

Tamaulipan thornscrub, the native vegetation type of northeast Mexico, has been severely fragmented for agriculture and induced grasslands for cattle grazing. Remnant fragments vary in size from a few hundred hectares to isolated trees. For a given individual tree, conditions vary from growing inside native vegetation to growing isolated inside agricultural fields or induced grasslands with varying degrees of competition, pollinators, and seed dispersers, which may influence individual reproductive fitness. In this study, we determined fruit and seed production as well as early seedling establishment for 10 trees inside thornscrub fragments and for 10 trees surrounded by agriculture. We found that the isolated trees produced more fruits and seeds than those inside native vegetation. The number of seedlings was, however, similar under both conditions, perhaps because of differential seed and survival mechanisms. Isolated trees seem capable of promoting tree encroachment in previously cleared habitats.

Morphology, anatomy, and ultrastructure of nectaries of 12 species belonging to five tribes of Rhamnaceae (Pomaderreae, Colletieae, Paliureae, and Gouanieae of the Ziziphoids clade and Rhamneae of the Rhamnoids clade) were studied by light and electron microscopy. Four types of nectaries were observed in this study. Species of the tribes Rhamneae, Gouanieae, Paliureae, and Cryptandra tomentosa Lindl. of the Pomaderreae tribe have annular nectaries. Siegfriedia darwinioides C.A. Gardner and Stenanthemum humile Benth. (Pomaderreae) have revolute nectaries, as do Colletia paradoxa (Spreng.) Escalante and Colletia spinosissima J.F. Gmel. (Colletieae). Retanilla patagonica (Speg.) Tortosa and Kentrothamnus weddellianus (Miers) M.C. Johnst. (Colletieae) have indistinct and adpressed nectaries, respectively. Nectar secretion occurs through modified nectary stomata in all species. Differences in the ultrastructure, mode of nectar secretion, and position of the nectaries are discussed. According to the organelles found in the nectary cells of all the species studied, granulocrine secretion is most likely to occur. Further research on these structures in additional species of this family could help to establish nectary homologies.

In Argentina Ocimum is represented by four species: Ocimum campechianum, Ocimum nudicaule, Ocimum ovatum, and Ocimum selloi. Complete descriptions for each of these taxa and illustrations, as well as a key for their identification, together with distribution maps in Argentina are given. Four new synonyms are here proposed, and lectotypes are here designated for the following species: Lumnitzera carnosa, Ocimum balansae, Ocimum hassleri var. acutatum, Ocimum micranthum, Ocimum neurophyllum, O. nudicaule, O. ovatum, O. selloi, O. selloi var. angustifolium, O. selloi f. serratum, and O. selloi f. subintegrifolium.

Two new species of Cyrtochilum are described and illustrated based on Colombian material. Both novelties are characterized by the triangular lip with basal callus and free petal apices. Information about the habitat of the new species and their distribution maps are presented.

We describe and illustrate Agastache sandersiana as a new species from northwestern Durango. This is a narrow endemic that clearly differs from all other species in the genus by leaf size, shape, and pubescence; inflorescence architecture; calyx tube length; corolla color; and corolla tube length. Additionally, an identification key to the Agastache species occurring in Durango, Mexico is provided.