This preliminary exploration of marine lichenized fungi (lichens) as bioindicators of water pollution examined the distribution of intertidal lichen communities in the Boston Harbor Islands National Recreation Area with respect to recorded pollution throughout the harbor. We found significant negative associations between pollution measurements and the health of the lichen community based on cover and species richness. We also observed significant differences in species composition between areas of higher pollution and areas of lower pollution, though not enough data are available to establish the pollution sensitivity or tolerance of individual species. We note that difficulties in the collection and identification of marine lichens hamper efforts to use them broadly as bioindicators. This study suggests that marine lichens could prove useful as bioindicators, but more research is needed to understand the differential effects of pollution on individual species as well as to establish practical procedures both for quantifying marine lichen community health and for widespread bioindication using marine lichens. Finally, one species collected during this study, Verrucaria ceuthocarpa, represents a first report for the Boston Harbor Islands National Recreation Area.

Urban forests of northeastern North America are often seen as degraded ecosystems with little ecological diversity or value. This is especially true given that native tree species declines in these forests have resulted from low recruitment caused by abundant exotic species, mortality from pathogens and pests, and severe deer browse. This study assessed tree composition and size structure of species found at the Robert B. Gordon Natural Area for Environmental Studies, an urban 51 ha forest fragment located 36 km west of Philadelphia, Pennsylvania. The study quantified and compared tree species from 15 plots located in mid- to late-successional forest stands. Species were categorized as native or exotic and resistant or nonresistant to deer browse. We quantified tree densities per species and measured diameter at breast height of all individuals > 2.5 cm and used this information to quantify relative importance values and assign trees to size classes. Natives Liriodendron tulipifera and Fagus grandifolia, and exotic Acer platanoides, dominated composition (i.e., 45.3% of total relative importance), with L. tulipifera most dominant. Natives had significantly greater densities than exotics in all size classes that included both categories, except for a 10–20 cm class, regardless of whether F. grandifolia, a prolific root sprouter, was included or excluded from comparisons. When F. grandifolia was excluded, nonresistant species had significantly greater densities than resistant ones in classes ranging from the smallest to larger classes. The prominence of nonresistant species in the smallest classes was unexpected given intense deer browsing.

In northeastern North America, alpine snowbank communities are rare plant assemblages that form in sheltered sites above treeline where late-lying snow provides insulation from late-season frosts and a longer-lasting source of water. We measured snowpack and studied community composition and plant traits at the species and community scales across the snowmelt gradient at snowbank sites on Mt. Washington, New Hampshire. We used nonmetric multidimensional scaling ordination and analysis of similarity to examine community composition across the snowmelt gradient and measured plant traits (height, leaf dry matter content, leaf area, and specific leaf area) of four focal species (Carex bigelowii, Chamaepericlymenum canadense, Clintonia borealis, and Maianthemum canadense). We assessed trait variability of the four focal species across the snowmelt gradient and evaluated community-weighted mean trait values and phenotypic plasticity between snowbank core and edge habitats. Analysis of similarity indicated that vascular plant diversity increased (p < 0.001), lichen and bryophyte cover decreased (p < 0.001; p < 0.025), and community-weighted mean leaf area increased (p < 0.001) in the core of snowbank communities where melting dates were later. Analysis of similarity indicated that vascular plant communities varied significantly across the snowmelt gradient. The transition in community composition and trait values across the snowmelt gradient are indicative of changing environmental conditions and ecosystem functions, though more research is needed to determine the extent to which phenotypic plasticity and ecotypic uniqueness influence trait expression of snowbank species. Genetic analysis may be necessary to evaluate population dynamics among isolated alpine communities, which may be vulnerable to climate change or displacement by exotic or lowland species.

Crowley's Ridge is a low, narrow, eroded ridge that rises above the uniformly flat alluvial floodplain in the northeastern quadrat of Arkansas. The ridge is geologically unique because it consists largely of wind-blown soil (loess) deposited during the late Pleistocene. During June 2008, quantitative data on the composition and structure of all strata of forest vegetation were collected from ten 0.1 ha plots at two general localities on the southern portion of Crowley's Ridge. Acer saccharum (sugar maple) was the leading dominant in the large/ medium-sized tree stratum, followed by Quercus rubra (northern red oak), Q. velutina (black oak) and Q. stellata (post oak), all with importance value indices > 10. Other species present included Carya alba (mockernut hickory), Fraxinus americana (white ash), Fagus grandifolia (American beech), and Liriodendron tulipifera (tulip-tree). Except for post oak, these trees tend to be characteristic of the classic Mixed Mesophytic Forest Region of the southeastern United States. In six of the 10 plots, the combined importance values of species typically associated with mixed mesophytic forests represented 84% to 100% of the large/ medium-sized tree stratum. Twenty-three different species were recorded in this stratum, a level of diversity that is comparable to a mixed mesophytic forest. As such, the data presented herein indicate that at least some forests on Crowley's Ridge apparently represent the westernmost examples of this forest type.