Gaps in the forest canopy can increase the diversity of tree regeneration. Understory shrubs also compete with tree seedlings for limited resources and may depress tree recruitment. We compared effects of shrub removal and canopy windthrow gaps on seedling recruitment and understory resource levels. Shrub removal, with the canopy left intact, was associated with increased levels of understory light and soil moisture and coincided with increased species richness and diversity of tree regeneration compared to both control plots and canopy gaps. Canopy windthrow gaps, however, resulted in a more than 500 fold increase in soil nitrate concentrations, and seedling growth rates that were twice as high as that observed with shrub removal. Our results suggest that gaps in the understory shrub layer and the overstory canopy may have complementary effects on resource availability with corresponding benefits to seedling establishment and growth.

The understory conditions of eastern hemlock stands in the Delaware Water Gap National Recreation Area have been altered by canopy decline caused by an exotic insect pest, the hemlock woolly adelgid. We consider the response of bryophytes to these changes, particularly increased availability of understory light and coarse woody debris (CWD). Pre-adelgid surveys and environmental measurements were taken at a network of 72 permanent plots in 1994 and 1995. Re-measurement of understory variables was conducted in 2003 and 2006. Bryophytes have responded to adelgid impacts through a sustained increase in plot-level richness, mainly achieved through a greater frequency of species occurring on CWD and to a lesser extent on bare soil in the plots. Greater gains in species richness took place in plots closer to the streams. Bryophyte responses to understory light availability and shrub density suggest that light availability may be more important for species maintenance than for species colonization. Orthodicranum montanum (Hedw.) Loeske had the greatest increase in frequency, occurring in two-thirds of all plots on one or more substrata by 2006. Several nitrophilous species had appeared by 2003 and 2006 including Brachythecium rutabulum (Hedw.) Schimp., which has now colonized almost one-third of the plots since the hemlock woolly adelgid invasion. Bryophytes are a significant component of the understory vegetation in eastern hemlock stands and this study is the first to document the dynamic nature of their response to hemlock woolly adelgid impacts.

The distribution of canopy trees can impose within-site patterns of soil properties and understory plant composition. At ten sites spanning a soil parent material gradient in northern Arizona Pinus ponderosa-Quercus gambelii forests, we compared soils and plant composition among five canopy types: openings, Pinus ponderosa single trees, Quercus gambelii single stems, dispersed clumps, and thickets. Soil texture on average did not differ significantly among canopy types, whereas Oi horizon thickness and weight, 0–15 cm soil loss-on-ignition, and gravimetric soil moisture differed significantly among three or more canopy types. Understory plant richness per 4 m² ranged from five species below P. ponderosa to 12 species in openings, with richness below Q. gambelii single stems significantly greater than below Q. gambelii thickets. C₄ graminoids (e.g., Aristida purpurea) inhabited openings, while C₃ species like Poa fendleriana also occurred below trees. The forbs Thalictrum fendleri and Lathyrus laetivirens were strongly associated with Q. gambelii dispersed clumps and thickets. We also conducted an experimental planting with T. fendleri that was consistent with these correlational results, with outplanted T. fendleri seedling survival 2–7 times greater when planted below Q. gambelii compared to openings. Previous research and our results suggest that understory species associated with Q. gambelii canopies vary regionally, but there are consistently some associated species. Canopy types affected understory vegetation similarly across soil parent materials, not supporting a hypothesis that positive plant interactions changed along soil gradients. Our results suggest that forest management that manipulates both the density and the pattern of trees, together with the growth forms of Q. gambelii trees, can induce within-site spatial patterns of soil properties and understory species.

The Mashomack Preserve on Shelter Island, New York contains one of the premier oak-dominated coastal plain forests in the northeastern U.S. It represents a unique opportunity to study woody species in juxtaposed forests that differ primarily in past land-use (logging versus agriculture). We researched how contrasting land-use history affected: 1) tree species composition, size, and age structure; 2) soil chemistry and morphology; 3) the dominance of Smilax, a native invasive shrub; and 4) the historical ecology and successional pathways. Randomly located plots were sampled for vegetation and soils in the unplowed interior forest versus the maritime forest that was cleared and/or plowed for agriculture and grazing in the 18^th and 19^th centuries and then abandoned after 1870. The upper soil profile was examined for soil nutrients and pH, the presence/absence of a plow layer (Ap) and for soil charcoal. Tree cores (N  =  130) were taken across both forest types to include the full range of species and diameter size classes to assess temporal and spatial variation in recruitment. Maritime forests are closer to the ocean shore and are dominated by Quercus velutina, Sassafras albidum, Carya glabra, and Q. alba, whereas the interior forests are dominated by Q. velutina, Acer rubrum, C. glabra, and Q. prinus. The interior forest plots appear to have continually supported forests, have soils that are somewhat doughtier and less fertile, and lack a plowed horizon, but have frequent soil charcoal as compared with the maritime forest. Formerly plowed and grazed maritime soils are more fertile and Q. alba has greater importance, while Q. velutina has lower importance. Following agricultural abandonment, the maritime forest understory became dominated by thickets of Smilax and presently has lower tree diversity than interior forests. Tree regeneration is sparse in both forest types due, at least in part, to intense browsing by white-tailed deer (Odocoileus virginianus). The interior forest exhibits a predictable successional pathway from mixed-oak to A. rubrum and Fagus grandifolia, which is not apparent in the maritime black oak forests. We believe that differences in overstory and understory composition, species diversity, and successional pathways between the two forest types can be mainly attributed to contrasting land-use history. Smilax is a super-dominant species that has profoundly influenced many ecological processes on the preserve and if left unchecked will continue to do so long into the future.

This study describes the principal changes in the flora of the Cayuga Region over the past 200 years. The region's flora has been thoroughly documented by botanists at different times but the changes have not before been synthesized. The region studied is approximately 10,000 km² surrounding Ithaca, NY, USA. The plant diversity of the Cayuga Region of New York has increased substantially over the past two centuries, as the gains of non-native plant species have far outnumbered the losses of natives. Of 1,265 vascular plant species native to the region, only 43 have been lost, despite large changes in land use and habitat areas. None of the species losses represent global extinction. There are no clear correlates or predictors for the species that disappeared. They were not all rare, nor were they predominantly in one kind of habitat, or from particular plant families. The majority of the 777 non-native plant species in the extant flora are rare or scarce within the Cayuga Region, and only a small number are of concern as aggressive invaders. Most of the non-natives are Old World herbaceous species of open, unforested habitats.

Sex expression was examined in two island populations of the monoecious Taxus canadensis at the Apostle Island National Lakeshore, USA. Long-term observations of tagged plants supported earlier published conclusions based on comparisons among populations of the effect of size and age on sex expression, measured as standardized phenotypic gender. As populations of plants increased in size and age, strobilus ratios became more male-biased and gender concordance increased. Male-biased plants remained male-biased and female-biased plants remained female-biased; gender switching was not a feature of either of these populations.

The two Taxus canadensis populations were mapped to examine spatial dispersion of plants and plant attributes, such as size, strobilus production, and gender. Frequency distribution of gender in both populations was significantly bimodal supporting earlier studies; this conclusion held even when small (typically male) plants with unstable gender were excluded from the analysis. Distribution of T. canadensis in both populations was clumped. Plant attributes showed some spatial autocorrelation, although the results were not consistent across populations or at different lag distances. Size and male strobilus production tended toward spatial autocorrelation in both populations, female strobilus production showed significant spatial autocorrelation on Manitou Island only at a few lag distances, and gender showed no spatial autocorrelation at any lag distance in either island population. The implication of these results for genetic versus environmental determination of sex expression in T. canadensis are briefly discussed.

Recognition of infraspecific taxa in Pteryxia terebinthina (vars. albiflora, californica, foeniculacea, and terebinthina) is controversial. Multivariate analysis of variance, principal component analysis, and discriminant analysis of 265 specimens representing the morphological variability and geographic distribution of the species complex were conducted to test the validity of these infraspecific taxa. Results show that var. terebinthina can be recognized by its unique fruit wing structure. There are statistically significant differences among the remaining varieties for most of the characters previously used to recognize these varieties, but all of these characters are overlapping among the taxa. No clearly separated clusters are revealed in the principal component analysis and discriminant analysis does not allow reliable recognition of the varieties. We therefore propose that this species complex be recognized as containing two varieties, foeniculacea and terebinthina.

Studies of wide-band tracheids (WBTs) have aroused the interest of researchers who have searched to understand their origin, function, and phylogenetic implications. The present research has the objective of studying the distribution of WBTs, together with anatomic aspects of vegetative organs in different stages of Pilosocereus aurisetus, in order to understand the occurrence of WBTs in columnar cacti. Transverse and longitudinal sections of the stem (apex, middle, and base) and the root were made. The epidermis was present in the photosynthetic stem, but was substituted by periderm which was already well established in the root. The differentiation of the cortex is visible in the middle of the stem, becoming homogeneous in the base. WBTs were observed in the base and middle of young stems (WBT monomorphic wood); common in stems of globular cacti. However, WBTs/fibrous dimorphic wood was observed in the base of adult stems, a result of the cambial activity producing vessel elements and fibers. This wood polymorphism of the Cactaceae can be interpreted as cambial variation, a common character of Caryophyllales. Due to the small size of the plant, the presence of WBTs in the young stem may be related to water retention necessary for its development, rather than to physical support of the plant.

Underground systems of Asteraceae species from the Brazilian Cerrado. The aim of this study was to describe the underground systems structure, the origin of the shoot buds, and to identify the storage reserve of seven Asteraceae species in order to understand the adaptive strategies of these species in burned Cerrado areas and their higher frequency in the floristic surveys for herbaceous and undershrub layers of this biome. The subterranean systems types—diffuse underground system, rhizophore, tuberous roots, and xylopodium—varied among the studied species, but all of them have high shoot bud-forming potential. Fructans of the inulin type were detected as storage substances. The presence of these characteristics on the underground systems could explain the frequency of these species in the floristic surveys from the Brazilian Cerrado, in which fire and seasonal drought are frequent. It is possible that the belowground bud banks in the Cerrado biome are as important as demonstrated in North American prairies where fire is also frequent. However, in the Cerrado, as demonstrated here, there are types of underground systems other than rhizomes that are usually described in the prairie. Understanding the anatomical features of these plants is one of the steps to appropriate conservation management of these species in the Cerrado.

The purpose of this research was to: (1) document the path of internal airflow, (2) describe and quantify tissues of internal airflow, and (3) determine if the amounts of aerenchyma in leaves, stems, and roots are relatively constant among plants of Rhizophora stylosa. Cork warts of leaves (average of 10.1 cork warts per mm² of leaf surface) are sites of air uptake. Cork warts deliver air to aerenchyma tissues near adaxial leaf surfaces (30% of total leaf volume). Air becomes pressurized within illuminated leaf blade aerenchyma by hygrometric pressurization and this air enters the petiole aerenchyma. In turn, the petiole aerenchyma joins the stem aerenchyma (5.5% of total stem area). Air descends the stem aerenchyma and then passes to the inner aerenchyma of stilt roots (about 15% of root cross-sectional area). Air descends in the inner aerenchyma of roots and eventually enters the smallest roots growing in anoxic substrates. From these terminal portions of roots, air ascends the outer aerenchyma of roots (73% of root area) where it may be released to the substrate via lenticels. If the amounts of aerenchyma in all leaves, stems, and stilt roots for whole plants are well correlated, it would further suggest that the relative amounts of these organs are specially suited for internal airflow. Data from 13 plants show that total aerenchyma volume of all leaves was highly correlated with total volume of aerenchyma in all stems for whole plants. Moreover, total volume of aerenchyma in all stems was highly correlated with total volume of outer aerenchyma in all roots for whole plants. Taken together, these data document the path of internal airflow in plants of Rhizophora stylosa and indicate that leaf, stem, and root growth are well regulated in plants of various sizes in accordance with this internal airflow.

This paper summarizes a broad range of studies that have examined influences of recent climate change on plant phenology or distribution. Spring events such as leafing and flowering have typically advanced, some by several weeks, with median advances of 4–5 d per degree Celsius. Autumn events, such as leaf coloring or leaf fall, have usually become delayed, though with more variability than spring events. Changes in summer events have been mixed. Phenological changes have varied geographically, as have recent temperature changes. Most studies of at least several decades duration show the initiation of rapid changes in the 1970s or 1980s, paralleling patterns of temperature change. Plants and animals in a given area have often responded at different rates to temperature change, which is likely to change patterns of interaction between plants and their pollinators and herbivores. Altitudinal changes in plant distributions have been demonstrated in several areas, especially in Scandinavia and in Mediterranean Europe, though these changes lag the measured temperature changes. Latitudinal changes in plant distribution have been demonstrated in only a few instances and it has been suggested that precipitation changes may have limited range shifts in response to warming in some areas. The observed and predicted changes in plant distribution and phenology have major implications for various ecological and evolutionary phenomena, including ecosystem productivity, species interactions, community structure, and conservation of biodiversity.

Corrections to the previously published vascular flora of the Caumsett State Historic Park are made here. We have deleted one genus and five species, and added three families, five genera and 16 species. The new totals for the Caumsett flora are: 104 families, 334 genera, and 635 species.