Invasive species impose severe biological and economic costs worldwide. In forested ecosystems, invasive species supplant native species, resulting in decreased biodiversity. Furthermore, human-mediated disturbances may stress native forest species and benefit invasive species that thrive in disturbed habitats. Anthropogenic changes to the landscape have caused unprecedented increases in white-tailed deer (Odocoileus virginianus) numbers, which has resulted in the degradation of understory native plant communities. We suggest that deer-mediated disturbance to understory communities facilitates the success of invaders in forests. Many North American forests experience both exotic plant invasion and deer overabundance, but the two problems have never been empirically linked. In this paper, we quantify deer effects on native and exotic understory herbs in a western Pennsylvania forest. We show that the percentage of bare ground and the relative abundances of the invasive herbs, Alliaria petiolata and Microstegium vimineum are significantly greater, while native plants are significantly smaller with a lower proportion flowering in deer access vs. deer exclusion plots. Our data support the idea that invader success is due in part to both preferential foraging by deer on native herbs that reduces their size and flowering status and the creation of open patches when deer are present. We conclude that deer overabundance facilitates the success of invasive species in forested ecosystems and that management will benefit by considering these factors jointly.

Amphibian populations are known, or thought to be, declining worldwide. Although protected natural areas may act as reservoirs of biological integrity and serve as benchmarks for comparison with unprotected areas, they are not immune from population declines and extinctions and should be monitored. Unfortunately, identifying survey sites and performing long-term fieldwork within such (often remote) areas involves a special set of problems. We used the USDA Natural Resource Conservation Service Soil Survey Geographic (SSURGO) Database to identify, a priori, potential habitat for aquatic-breeding amphibians on North and South Manitou Islands, Sleeping Bear Dunes National Lakeshore, Michigan, and compared the results to those obtained using National Wetland Inventory (NWI) data. The SSURGO approach identified more target sites for surveys than the NWI approach, and it identified more small and ephemeral wetlands. Field surveys used a combination of daytime call surveys, nighttime call surveys, and perimeter surveys. We found that sites that would not have been identified with NWI data often contained amphibians and, in one case, contained wetland-breeding species that would not have been found using NWI data. Our technique allows for easy a priori identification of numerous survey sites that might not be identified using other sources of spatial information. We recognize, however, that the most effective site identification and survey techniques will likely use a combination of methods in addition to those described here.

Many forests, including the mixed-conifer forest of the Sierra Nevada, California, historically experienced a fire regime that generated considerable within- and among-fire environmental variability. Fire suppression has resulted in a heavier, more continuous fuel bed, which can cause today's prescribed fires to be considerably more homogeneous. To evaluate the potential importance of variability in fire severity on post-fire plant communities, I conducted an experiment to test whether understory species respond differently to sites burned under a heavy fuel load versus sites that burned under a light fuel load. Woody fuel was added or removed from small forest plots in order to manipulate the fire severity during prescribed fire. The fuel load manipulations affected which species survived fire as well as which species germinated after fire. Seven species (Chimaphila menziesii, Chrysolepis sempervirens, Osmorhiza chilensis, Pyrola picta, Phacelia hydrophylloides, Rubus parviflorus, and Smilacina racemosa) were unable to survive fire in either treatment. Four species (Bromus laevipes, Galium sparsiflorum, Rubus glaucifolius, and Symphoricarpos mollis) survived more often on sites that were burned under a light fuel load. Several fire-stimulated species (Calystegia malacophylla, Cryptantha sp., Gayophytum eriospermum, Solatium xanti, Arctostaphylos patula, Ceanothus parvifolius, and Lotus crassifolius) germinated after fire regardless of fuel load, but others (Claytonia perfoliata, Ceanothus cordulatus, Prunus emarginata, and Ribes tularense) appeared more often on the light fuel treatments. Seedlings of Abies concolor germinated more often on the sites that burned under heavy fuel conditions. The varying responses of different species suggest that small-scale variations in fuel load may cause heterogeneous patterns of surface fire severity, which in turn may contribute to maintaining floral diversity in the mixed-conifer forest understory. In order to conserve native understory plant diversity, fire management efforts to restore these forests might consider spatial heterogeneity in fire severity as a management objective.

Grassy openings have a high conservation value because they provide habitat for a number of rare and endemic species and contribute to landscape level biodiversity. However, these communities are at risk because tree encroachment causes the conversion of grassy openings into closed-canopy forest. Many land managers have taken an active position in maintaining these openings by introducing disturbances such as fire, grazing, or mowing to slow or halt the invasion of tree species. The objective of this study was to trace the closure of grassy openings, in the absence of active management, and identify whether the forest that developed was unique in tree and shrub composition and structure or whether it mirrored the surrounding forest matrix. Our study site was an area with historical grassy openings visible on a 1937 aerial photograph. We sampled the vegetation in these former openings, now closed-canopy forest, and compared them with paired plots on similar aspects and elevations but forested in the 1937 photographs. The tree and shrub composition in the former grassy openings was similar to the composition in the adjacent forested areas and was also similar to regional second-growth forests. Thus, we concluded that in the absence of active restoration, rare grassy openings convert to vegetation communities that are similar to the regional forest conditions.

We studied effects of fertilization and time of cutting on the regeneration of cutleaf teasel (Dipsacus laciniatus L.) at the Mascoutin Recreation Area at Clinton Lake, Dewitt County, Illinois, for two growing seasons. D. laciniatus is an exotic European invasive species that infests natural habitats across much of the United States and southern Canada. We established fourteen 5.0-m × 5.0-m paired plots, seven fertilized and seven unfertilized. Each set of paired plots was assigned one of seven cutting treatments, including no cutting, or one of six cutting times from 3 June to 10 August 2002. We measured stem height, number of heads per individual plant, number of seeds per head, and seed viability. We found no significant difference between plant heights or number of heads per individual in fertilized versus unfertilized plots. Reproductive success significantly increased when D. laciniatus had more time to grow after cutting. If cutting occurred before flower buds opened in early July, no significant difference in number of heads produced was found between cut and uncut D. laciniatus. If cutting occurred after flowers developed, then the stalk height, number of heads, seeds produced per plant, and total number of viable seeds all significantly decreased. Therefore, it appears that mowing areas containing cutleaf teasel in the Midwest may be an effective control, but only if performed after rosettes have committed to bolting, before seeds are viable, and late enough in the growing season to prevent reproductive regrowth.

Aconitum noveboracense A. Gray ex Coville (northern monkshood) is a federally threatened plant species of the blue-flowered Aconitum section (Napellus) that occurs in Iowa, Wisconsin, Ohio, and New York, with most populations in Iowa. Monitoring of 12 populations in Iowa over a 15-year period showed substantial periodic variation in all population parameters, although less variation in adult density. Variation among sites was only detected for the proportion of quadrats with fruiting plants, and overall, adult and juvenile density. Our analysis provided a mixed view of the status of this species. On one hand, after a substantial decline between the 1994/95 and 2001/02 sample intervals, overall population density and density of each life stage increased and nearly recovered between the 2001/02 and 2004/05 sample intervals. Conversely, all our measures of reproduction - number of fruits/plant, proportion of quadrats with fruiting plants, number of fruits/node - indicated reduced vigor, as in the same intervals these measures declined and did not recover. Soil temperature was highly correlated with juvenile and adult density. Measuring additional biotic and abiotic factors should be incorporated into future monitoring. Local-scale abiotic factors that could influence variation in adult and juvenile density include light levels, drought, distance to cold air vents, soil moisture, nutrient levels, and humidity. Biotic factors, particularly herbivores, pollinator availability, and garlic mustard (Alliaria petiolata (M. Bieb.) Cavara & Grande), are also likely to have an impact on the Iowa Aconitum populations.

Itasca State Park, located in the northern central portion of Minnesota, is challenged with maintaining a pine forest covertype, yet regeneration failures may allow much of the park to succeed to northern hardwoods. Efforts to improve pine regeneration and growth have included deer exclosures and prescribed burning to reduce competing vegetation. We revisited Itasca's Mary Lake deer exclosure 66 years after establishment to compare stand development, structure, and white pine (Pinus strobus L.) regeneration and growth with that of adjacent plots that have been: (1) untreated and (2) recently repeatedly under-burned. Overstory structure and composition was similar among all three treatments, and mid- and understory structures were similar in the treatments subject to deer browse. Sapling and midstory white pine were only present in the exclosure. White pine regeneration was present in all treatments and most abundant in the burned treatment, but was restricted to the smallest height class and consistently overtopped by the shrub layer. Regeneration, sapling, and midstory layer tree densities were highest within the deer exclosure, as was white pine height growth. The untreated plot lacked young pine and will likely succeed to northern hardwoods with a shrub understory. The three-fire sequence of the burned treatment increased the abundance of white pine regeneration at this site, but may require additional measures to control competing vegetation to allow that regeneration to ascend into the sapling layer.

White-tailed deer (Odocoileus virginianus Zimmerman) have been labeled a keystone herbivore in forests of the midwestern United States, particularly as deer have increased over the past century due to forest fragmentation, reduction of natural predators, reduced hunting, and mild winters. Deer browsing in the Apostle Islands National Lakeshore has had a pronounced effect on formerly large continuous patches of reproductive Canada yew (Taxus canadensis Marshall). In order to compare understory plant communities in 2005 to those at sites sampled in 1958, we resurveyed 32 forest sites on islands that remained free of deer throughout this period, on islands that retained deer, and on islands that gained or lost deer. Multivariate analyses reveal that deer have strong effects on the type of change in the forest understory. Plant communities on sites with long-term deer pressure are becoming increasingly different from those on sites that have never had deer. Four new understory species were detected at these sites, two other species increased by more than 20%, while eight decreased by more than 20%. While grasses and sedges were favored on sites that maintained or gained deer, perennial forbs declined conspicuously on these sites. The recovery of understories on islands where deer were removed suggests that such actions can effectively restore suitable habitat conditions for certain species sensitive to deer herbivory.

Biological invasion is a leading threat to the ecological integrity of forest ecosystems around the world. The objective of our study was to examine the relationship between the abundance of non-native species in the vegetation and the soil seed bank to abiotic factors and distance from the nearest forest edge. We identified and estimated the abundance of plant species in sixty-two 0.4 ha permanent plots in natural areas across the Shawnee National Forest in southern Illinois in late spring and summer 2002. The distance of each plot to the closest forest edge was determined using GIS. A 550 cm³ soil core was extracted from five random points within each of the plots in August 2002 to allow measurement of soil nutrient levels and estimates of the abundance of exotic and native species in the soil seed bank. Soils from these cores were placed in trays in a greenhouse on 10 January 2003. Seedlings emerging from the soil cores were identified and tallied every two weeks until no further seed germination was observed. The plots were located deep in the forest interior (up to 730 m), yet forest edge effects predominate. Distance from forest edges was negatively related to density of both native and non-native species in the seed bank. The largest numbers of non-natives in the seed bank were present in those plots closest to the forest edge. None of the nine important abiotic factors (K, Ca, P, Mg, pH, CEC, and OM, % silt, canopy opening) measured in this study was related to the seed bank density of the native and non-native species. Potassium was negatively and calcium was positively related to richness of understory native species and distance from forest edge. Phosphorus, Mg, pH, CEC, % silt, OM, and canopy opening were not related to the richness of native species and distance. Commelina communis, Lonicera japonica, Microstegium vimineum, and Rosa multiflora were non-native species present in the understory vegetation while Barbarea vulgaris, Cardamine hirsuta, Lactuca serriola, Lespedeza cuneata, M. vimineum, Mollugo verticillata, and Stellaria media were non-native species present in the seed bank. The discordance between non-native species richness in the seed bank and vegetation community indicates that management of invasive species must extend beyond eradication of non-natives in the aboveground vegetation. Land and forest managers should eradicate seedlings of non-native species before they reach seed production stage to decrease their accumulation in the seed bank even at sites located at a great distance from the forest edge.

Prairie dropseed (Sporobolus heterolepis [A. Gray] A. Gray) is a warm-season grass that is an important component of remnant tallgrass prairies of North America, but is rarely found in restorations. We conducted three experiments to determine germination rates of prairie dropseed under different conditions in an attempt to potentially increase its successful establishment under field conditions. In the first experiment, we evaluated the duration of cold-moist stratification on the germination of prairie dropseed. Seeds were cold-moist stratified for 0, 30, or 60-d at 4 °C and then placed in a dark growth chamber at 26 °C. The other two experiments consisted of seeds planted in three different soil media: 1:1:1 soil:peat:perlite mixture, non-compacted field soil, and compacted field soil. They were then exposed to full irradiance or 50% shade. Germination was highest for seeds cold-moist stratified for 30 or 60 d. Seeds planted in either non-compacted or compacted field soil had higher germination rates than the 1:1:1 mixture in both full irradiance and 50% shade. We conclude that prairie dropseed has higher germination percentage after a period of cold-moist stratification. While our results indicate that seeds germinate better in field soil, germination rates were low compared to the amount of viable seed. It also appears that seed of prairie dropseed germinate at relatively higher levels under partial shade.