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Irregularly disturbed forests surrounding crop fields in agricultural landscapes often serve as ecological buffers that separate undesirable agricultural elements such as agrichemicals and weedy species from adjacent ecosystems. However, the nature of this interface between fields and forests remains little studied, particularly within the context of how species composition changes with field distance and how far exotic species penetrate into forest interiors. In three agricultural landscapes in the North Carolina Piedmont, we surveyed plant communities in multi-scale, nested quadrats arrayed along transects perpendicular to field boundaries and penetrating >200 m into adjacent forests. Rates of species turnover, patterns of species richness, and the distribution of exotic species were assessed for 18 transects. Plant communities exhibited high rates of compositional turnover within 50 m of field boundaries, but species turnover was considerably reduced beyond this threshold. Vegetation composition within borders immediately adjacent to cornfields was dominated by a relatively predictable set of weedy forb and graminoid species, of which a substantial proportion was exotic. Composition of surrounding forest communities more reflected local environmental conditions and contained few exotic species overall. Species richness was not influenced by field proximity. We suggest that agricultural influences on landscape-scale vegetation patterns are most apparent in plant communities located very close (<50 m) to continuous agricultural operations. Although weed communities associated with agricultural management are represented by a large pool of exotic species, relatively few of these species are able to penetrate forest boundaries.
Ericaceous shrubs can influence soil properties in many ecosystems. In this study, we examined how soil and forest floor properties vary among sites with different ericaceous evergreen shrub basal area in the southern Appalachian mountains. We randomly located plots along transects that included open understories and understories with varying amounts of Rhododendron maximum (rosebay rhododendron) and Kalmia latifolia (mountain laurel) at three sites. The three sites were a mid-elevation ridge, a low-elevation cove, and a high-elevation southwest-facing slope. Basal area of R. maximum was more correlated with soil properties of the forest floor than was K. latifolia. Increasing R. maximum basal area was correlated with increasing mass of lower quality litter and humus as indicated by higher C∶N ratios. Moreover, this correlation supports our prediction that understory evergreen shrubs may have considerable effect on forest floor resource heterogeneity in mature stands.
During the period of 2003 to 2008, samples for isolation of dictyostelid cellular slime molds (dictyostelids) were collected from 17 localities throughout the state of Arkansas. The localities sampled included at least two examples in each of the six natural regions (Arkansas River Valley, Ozark Plateau, Ouachita Mountains, Gulf Coastal Plain, Crowley's Ridge and Mississippi Alluvial Plain) recognized for the State. The 167 samples collected from the 17 localities yielded a total of 2,082 individual clones representing 13 different species plus one form that could not be assigned to any described species. Six of the species recovered are reported from Arkansas for the first time, bringing the total number known from the State to 16. Polysphondylium pallidum was by far the most abundant species, comprising almost 50% of all isolates. Three other species (Dictyostelium minutum, P. violaceum and D. purpureum) made up approximately 30% of all remaining isolates, and the nine other species recovered were uncommon to rare. Two isolates of what appears to be Dictyostelium rhizopodium, a species in which the sorocarps have crampon bases, represent one of the northernmost known occurrences of a dictyostelid with this feature, which is characteristically found in species associated with tropical and subtropical regions of the world. Two species (D. caveatum and D. rosarium) reported previously from Arkansas were not isolated in the present study.
The inflorescences of kudzu, Pueraria montana, and the groundnut, Apios americana, have extrafloral nectaries at the base of each multiple-flowered fascicle. In P. montana, the EFNs lie under the lateral flowers and appear to become active and accessible only when the covering flower abscises and drops. In A. americana, there is one EFN per fascicle, representing an aborted secondary short-shoot. Five species of ants were observed visiting P. montana EFNs and six species at A. americana EFNs (four of which were found on both). EFN-related behaviors varied among ant species, but not within ant species between plants. The location and timing of these heretofore overlooked EFNs suggests a role in protecting early developing seeds. Thus, the low seed set reported for P. montana in its introduced range on the one hand and for A. americana in cultivation on the other might be explained by a shortage of ant mutualists in these atypical situations.
In 1710 and 1711, naturalist and author John Lawson sent collections of dried plants from eastern North Carolina to James Petiver in England. Two hundred and ninety five of these specimens survived and are maintained in the Sloane Herbarium of the Natural History Museum in London. Many of the specimens bear tags in Lawson's hand giving the date, location, and notes describing use or habitat. One hundred and one taxa are listed here along with discussion of some of the notes that connect Lawson's plant collecting to important events in his life and to the colonial history of North Carolina. The story concerning how these specimens were collected and maintained provides insight into the methods of botanical science in the early eighteenth century.
A vascular plant survey of Ledges State Park (Boone County, Iowa; 482 ha) was conducted from 2005 to 2008 during which 697 taxa were encountered. A search of the literature and the holdings of Iowa State University's Ada Hayden Herbarium (ISC) revealed 79 additional taxa found in the Park. This total of 776 taxa adds 306 to the floras published in two previous floristic studies of the Park. An annotated checklist was prepared that includes the origin, habitat preferences, and collection history for each taxon. This study reports 31 taxa not included in Eilers and Roosa's 1994 checklist of Iowa's vascular flora, including a population of Oenanthe that may represent a new species. Thirteen taxa documented from the Park are listed as endangered, threatened, or special concern by the Iowa Department of Natural Resources. The results of this survey provide knowledge of the extent of invasive species in the Park and facilitate analysis of floristic change. Survey results also provide a more thorough understanding of Iowa's flora, including updated species' distributions and the status of rare plants. The study reveals the need for a computer database of specimens in Iowa's herbaria and an online, regularly updated checklist of Iowa vascular plants. Like Ledges, many parks fulfill important conservation roles in providing a haven for sensitive species and uncommon plant communities. To ensure the future integrity of all of Iowa's state parks, we recommend increased support for scientific research and conservation.
Bupleurum L., with ca. 150 species, is one of the largest genera in the Apiaceae (Umbelliferae). The genus has a broad distribution in the Northern Hemisphere, and it is represented in North America by the native and possibly endemic species Bupleurum americanum J.M. Coult. & Rose, and by three introduced species: B. lancifolium Hornem., B. rotundifolium L., and B. odontites L. Here we report the occurrence of a new alien species of the genus in North America: Bupleurum gerardii All. We present a general characterization of the species and discuss the possible origin of the populations that have been found in Tennessee and Virginia. In addition, we confirm the records of B. odontites for the states of Maryland, Massachusetts and Oregon. All previous citations of B. odontites in Virginia refer to material of B. gerardii. The history of the discovery of this species in North America suggests that the treatment of sparingly naturalized taxa in floras is erratic and identifications of these species suspect.