The present study describes the occurrence of mucilage ducts within Polygalaceae. Polygala angulata DC. is a species from the Brazilian cerrado that possesses secretory ducts in the stem angles of primary growth. First, a schizogeneous process and later, a lytic process both take place in the course of secretory duct formation, characterizing the development of the glands as schizolysigenous. Histochemical tests confirm the mucilage nature of the exudate. The presumable functions of this gland are associated with xeromorphic adaptation of this species to the cerrado environment.

Environmental stresses and disturbances are common in terrestrial ecosystems. Clonal integration and foraging behavior are often, but not always, beneficial for clonal plants grown in heterogeneous stressful environments. In this study, clonal fragments of the clonal perennial herb, Aeluropus sinensis (Debeaux) Tzvel (Poaceae), were grown with stolons connected or severed at five salinity levels (0, 50, 100, 200, and 400 mmol L⁻¹ NaCl). In each clonal fragment, the apical ramet was exposed to crude oil on the sediment surface while the basal ramet was not. We proposed three possible scenarios: growth of the apical ramet subjected to crude oil would be (1) enhanced, (2) limited, or (3) not affected by clonal integration. Results supported scenario (2). Responses to crude oil differed between plants grown at low and high salinity levels. For A. sinensis, at high salinity levels, clonal integration promoted habitat selection by decreasing biomass of apical parts to escape the oil polluted habitats and increasing clonal growth of basal parts to select the unpolluted habitats, while at low salinity levels, connection did not influence growth of the basal or apical parts. Salinity modulates the behavior of a clonal plant subjected to heterogeneous crude oil contamination, at least in A. sinensis.

Hybridization in plants can be common, may lead to increased genetic variation, and in some instances the formation of new species. For endangered species, hybridization can introduce novel genetic variation and potentially increase genetic diversity. In contrast, hybridization can negatively affect an endangered species or population by introducing maladaptive alleles into locally adapted lineages or lead to the homogenization of once distinct lineages. We used microsatellites, AFLP markers, and morphological data to identify potential hybridization between the endangered Roan Mountain bluet (Houstonia purpurea var. montana) and its commonly occurring congener (H. purpurea var. purpurea). We used these data to clarify the taxonomic relationship of these varieties and to assess population structuring of the Roan Mountain bluet. The results showed that these lineages are distinct and few individuals exhibited admixture in several populations. Additionally, the results showed there is genetic population structure among the remaining populations of H. purpurea var. montana, which is consistent with other mountaintop species. Our results show that Roan Mountain bluet populations should be protected to maintain genetic diversity and monitored to assess future hybridization, and additional studies that comprise a greater population sampling would provide more information.

Physaria filiformis, a threatened species of calcareous glade communities, blooms profusely within the Rocky Barrens Conservation Area (Missouri) under a program of controlled burns. Flowers visited by insect foragers in 2008 and 2009 had a mean > 35 and > 50 germinating grains on their stigmas respectively and a mean of 1.96–2.0 pollen tubes entering their ovaries (mean of 4 ovules/ovary). Results of controlled hand-pollinations conducted in situ in 2009 showed that this species had a negligible rate of self-pollination (mechanical autogamy) and showed classic Brassica-type, early-acting self-incompatibility. Each dissected flower had nectar glands and each seasonal population was visited by insects representing four insect orders; Coleoptera, Diptera, Lepidoptera and Hymenoptera. The most commonly collected floral foragers found to carry the pollen of the host flower were male and female native bees representing 38 species in the Andrenidae, Apidae, Colletidae, Halictidae, Megachilidae and the naturalized Apis mellifera. Only four of these species (11%) were collected in all three years, but these four accounted for slightly more than a third of all individual bees collected. None of the bees were known specialists on flowers of the Brassicaceae and only two species were habitat (glade) specialists. As P. filiformis is an obligate out-breeder but a generalist entomophile we suggest that future management plans include conservation and management of adjacent non-glade habitats to sustain the diverse range of pollinators.

The seed ecology of the federally endangered shrub, Lindera melissifolia was investigated to determine if this aspect of the species life history contributes to the rarity of the species. Lindera melissifolia has the capacity to form a short-lived (two growing seasons) persistent soil seed bank if fruit pulp remains on seeds following dispersal and subsequent winter flooding occurs. Seeds, both with or without pulp (i.e., mesocarp and exocarp), exhibited tolerance to submergence, but were not hydrochorous. Following 6–12 weeks cold stratification (5° or 5/1° C) or submersion in cold water (5/1° C) for 12 weeks, ≥ 63% of seeds germinated when incubated in light and at temperatures of 35/20° and 30/20° C. When incubated in darkness, 100% of seeds germinated following 6 weeks of cold stratification. Giberrelic acid was moderately effective in breaking dormancy. Collectively, our results indicate that seeds of L. melissifolia have nondeep physiological dormancy. Aspects of the seed ecology of L. melissifolia that may contribute to continued rarity of the species include absence of a long-term persistent soil seed bank, no obvious mechanism of long-distance dispersal, and late season germination that prevents seedling growth to a sufficient size for survival prior to cold temperatures and flooding.

Bark-stripping, or partial cambial mortality, is characteristic of Rocky Mountain bristlecone pine (Pinus aristata). The cause of this phenomenon is unknown, but previous work has shown a correlation between stripping and wind directions. We examined bark-stripping patterns in ten Pinus aristata stands in Colorado. For every strip, we recorded its relative position on the trunk and the direction of the strip top and bottom. Strips were assigned to one of 10 class-position types based on their relative lengths and positions. Mean top and bottom strip directions ranged from ∼225° to due north (0°). Site aspect ranged from 98° to 249°, whereas estimated wind direction ranged from 261° to 30°. Almost all of the small strips were on the lower half of the trunk. The directions of small strips near trunk bases were widely dispersed, whereas small strips higher on the trunk were more narrowly dispersed and oriented close to wind direction. Patterns of stripping and of abrasion of pencils fastened to trunks suggest that most strips that develop into larger ones are initiated by wind abrasion and extend primarily upward. Our findings are consistent with the model of Matthes et al. (2002) for the formation and possible function of bark-stripping.

We evaluated the impact of long-term over-browsing by white-tailed deer on the diversity and density of trees in a forest in the Allegheny High Plateau region of central Pennsylvania. We compared tree diversity and density inside a 60 year-old deer exclosure to an adjacent reference site. Browsing caused a 55–100% decline in density of four tree species (Prunus serotina, Acer saccharum, Betula lenta, Cornus alternifolia) and created a forest dominated (> 70% of all stems) by Acer pensylvanicum, an understory tree that is known to be highly browse-tolerant. The total density of trees that are capable of ascending into the canopy (i.e., non subcanopy tree species) declined by 85%. Browsing caused a significant decline in both mean species richness and Shannon diversity and created communities that contrasted significantly in tree species composition (ANOSIM, R  =  0.8105, P < 0.0001). Our results suggest that long-term over-browsing can create low density, depauperate communities where dominance is concentrated in only a few browse-resistant species (Acer pensylvanicum and Fagus grandifolia; 82% of all individuals vs. 37% inside the exclosure). We suggest that this may lead to novel forest dynamics in the event of a large canopy disturbance because these two species were never co-dominant in this region and the beech saplings (typically root sprouts) will likely succumb to future bouts of beech bark disease. Our results combined with those of many other studies call for the long-term reduction in the size of the deer herd throughout this region.

Population dynamics studies allow us to address three of the most basic questions essential to the creation of plans for species management and conservation. Specifically: what the population status is; what the stages or demographic processes that have the greatest impact on the population growth rate (λ) are; and what the probabilities of quasi-extinction for the species of interest are. Despite the importance of this type of research, demographic studies on vascular epiphytes are scarce. Epiphytes are key elements in the functioning of the ecosystems in which they live, as they enhance biodiversity, establish numerous interactions with other plants and animals, and are direct participants in the flow of nutrients and water. In spite of the importance of this group, population dynamics studies have only been performed on 2 of the 83 families of epiphytes. The three main challenges for field research are the difficulty of accessing epiphytes in their native environments, the combination of the vertical and horizontal distribution of these species, and the additional consideration of addressing the effects of phorophyte dynamics on epiphyte populations. This paper is designed to be the practical complement to a theoretical background in the population dynamics of epiphytes. It addresses both study design and practical issues of field work in the interest of encouraging the development of demographic studies of this form of life.

A naturally occurring, reproducing population of Betula nigra L. (River Birch) has been collected for the first time on Long Island, NY, in a recharge basin located in Huntington Station, Suffolk Co. This is the first verifiable collection for both the county and the island and represents a new and disjunct population for the species. A review of reported past occurrences in the literature for Betula nigra on Long Island is discussed.