Non-native Plant Species Richness Research Articles

Non-native plant species richness and influence of greenhouses and human populations in the conterminous United States

BackgroundOne issue in invasive plant ecology is identification of the factors related to the invasion process that increase number of non-native species. When invasion by non-native species increases, so does the probability that some non-native species will become harmful, or classified as invasive species, which disrupt natural ecosystems with attendant economic and social costs. I quantified patterns of how non-native species richness varied with vegetation types and human populations. To evaluate the relative importance of different predictor variables for invasion pathways in the conterminous United States, I modeled non-native plant species richness by county compared to current and historical human populations; greenhouses and nurseries; railroads, pipelines, transmission lines, and oil and gas wells; and land covers of impervious surface, development intensity categories, agriculture, and vegetation types. I also modeled these variables within vegetation types, excluding vegetation variables.ResultsTo summarize patterns, non-native plant species richness increased from 72 to 200 with increasing human population density classes. Forests and forest land use mosaics had the greatest mean number of non-native plant species, ranging from 121 to 166, whereas grasslands and grassland mosaics had the least number of non-native plant species, about 70. For modeling variable importance, all combined variables had R2 values of 56% (random forests regressor) and 54% (cubist regressor) for predictions of withheld observations of non-native plant species richness, with greenhouse density and percent forestlands as most influential variables. Single variables of greenhouses (R2 = 29%), historical and current human populations (R2 = 27% and 23%), impervious surface (25%), and medium intensity development (23%) were most associated with non-native plant species richness. For vegetation types, greenhouse and historical human population densities were influential variables particularly in forestlands, shrublands, and wetlands.ConclusionsBased on these models, human population measures and horticultural locations of greenhouses and plant nurseries may have stronger relationships than measures of land use disturbance and transport with non-native plant species richness.

Functional traits explain non-native plant species richness and occupancy on northern New Zealand islands

Plant functional traits can greatly influence invasion success on islands. However, interrelationships between traits and invasion success are rarely integrated with the island biogeography theory. Here, we explored relations between functional traits and plant distributions to assess which traits are associated with invasion success (i.e. high island occupancy), test whether non-native richness and seed mass of species with distinct growth forms and dispersal modes vary differently with island characteristics (e.g. area, isolation, exposure to ocean-borne disturbances, distance from the nearest urban area, and whether islands were managed for conservation), and whether results differ from native species. We assembled a database of 264 northern New Zealand offshore islands, amalgamating species lists from field surveys and previously published data, and comprising 822 native and 855 non-native species. Non-native graminoids occurred on islands more frequently than forbs and woody species, and long-distance dispersal modes (wind, animal, unspecialized) more than species with short-distance dispersal modes. Most differences among trait categories of non-native species were associated with human-related variables (i.e. distance from the nearest urban area, and whether islands were conservation areas). Non-native plant species with high island occupancy were less commonly associated with human-related variables than non-native species with low island occupancy. Instead, they were more similar in their distributional patterns to native species within the same trait category, suggesting comparable processes regulate both sets of species. Our results illustrate that integrating trait-based approaches in the island biogeography framework can be a useful tool in understanding and predicting plant invasions.

Patterns in urban butterflies and spontaneous plants across a University campus in Japan

University campuses often contain contiguous areas of urban green space (UGS) which are otherwise scarce in large cities and, thus, may provide critical habitat for numerous species. In this study, we evaluate butterfly and plant diversity at Chiba University in Japan from five UGS types, including intensive green roofs, meadows, roadsides, open spaces, and community gardens. Surveying non-destructively every two weeks from June to November 2010, we identified 707 individual butterflies to 25 species from five families, including red-listed species (e.g. Parantica sita Kollar, 1844). However, one species, Pseudozizeeria maha Kollar, 1848, represented over 50% of all individuals surveyed. Butterflies in the family Papilionidae showed strong preference for roadside habitat, indicating the importance of ‘butterfly flyways’ and contiguous habitat corridors on University campuses. Butterfly richness and abundance was significantly different between UGS types and highest in the community garden and roadsides. We recorded 70 garden plant species and 117 spontaneous plant species (which grew opportunistically, without design input), of which 58% were native. Total plant richness was positively correlated with butterfly species richness, and non-native spontaneous plant species richness was positively correlated with butterfly richness, abundance, diversity, and evenness. Additionally, 76% of the spontaneous species identified were determined to be used by butterflies as larval hosts or for adult feeding. Identification of spontaneous plant species and use of selective weeding should be included in landscape management planning on campuses to promote butterflies, which can act as ambassadors for biodiversity conservation and help connect people to nature.

Length of cultivation determines native and non-native weed richness in crop fields worldwide

Socio-economic factors often determine the extent to which different global regions have been invaded by non-native plant species, yet few studies examine whether such variables are similarly important for native species richness. In contrast to previous studies that have assembled regional floras for comparison, we examine global patterns of non-native and native plant species richness within a single, globally distributed ecosystem: cultivated wheat fields. Native species richness increased with the historic length of wheat cultivation, total wheat harvested area and arable land area in a country. In contrast, non-native weed species richness declined with increasing length of wheat cultivation, higher fertilizer inputs, and lower absolute latitude. The low percentage of native species in countries with a short history of wheat cultivation suggests that the invasion of crop fields by native plants takes longer than the migration of non-native weed species pre-adapted to crop fields in other parts of the world. Seed contaminants in grain imports are probably one of the main sources of non-native weeds, especially for regions with more recent wheat cultivation histories. To date there has been a tendency for research on agricultural weeds to be dissociated from that of plant invasions, yet we show how cultivation history has shaped the weed flora and why non-native weeds are perceived as such a problem in New World agriculture, as well as confirming at a global scale the role of crop husbandry and agricultural extent on weed floras.

Plant diversity drives global patterns of insect invasions

During the last two centuries, thousands of insect species have been transported (largely inadvertently) and established outside of their native ranges worldwide, some with catastrophic ecological and economic impacts. Global variation in numbers of invading species depends on geographic variation in propagule pressure and heterogeneity of environmental resistance to invasions. Elton’s diversity-invasibility hypothesis, proposed over sixty years ago, has been widely explored for plants but little is known on how biodiversity affects insect invasions. Here we use species inventories from 44 land areas, ranging from small oceanic islands to entire continents in various world regions, to show that numbers of established insect species are primarily driven by diversity of plants, with both native and non-native plant species richness being the strongest predictor of insect invasions. We find that at large spatial scales, plant diversity directly explains variation in non-native insect species richness among world regions, while geographic factors such as land area, climate and insularity largely affect insect invasions indirectly via their effects on local plant richness.

Assessing threats of non-native species to native freshwater biodiversity: Conservation priorities for the United States

Non-native species pose one of the greatest threats to native biodiversity, and can have severe negative impacts in freshwater ecosystems. Identifying regions of spatial overlap between high freshwater biodiversity and high invasion pressure may thus better inform the prioritization of freshwater conservation efforts. We employ geospatial analysis of species distribution data to investigate the potential threat of non-native species to aquatic animal taxa across the continental United States. We mapped non-native aquatic plant and animal species richness and cumulative invasion pressure to estimate overall negative impact associated with species introductions. These distributions were compared to distributions of native aquatic animal taxa derived from the International Union for the Conservation of Nature (IUCN) database. To identify hotspots of native biodiversity we mapped total species richness, number of threatened and endangered species, and a community index of species rarity calculated at the watershed scale. An overall priority index allowed identification of watersheds experiencing high pressure from non-native species and also exhibiting high native biodiversity conservation value. While priority regions are roughly consistent with previously reported prioritization maps for the US, we also recognize novel priority areas characterized by moderate-to-high native diversity but extremely high invasion pressure. We further compared priority areas with existing conservation protections as well as projected future threats associated with land use change. Our findings suggest that many regions of elevated freshwater biodiversity value are compromised by high invasion pressure, and are poorly safeguarded by existing conservation mechanisms and are likely to experience significant additional stresses in the future.

Forest habitat invasions – Who with whom, where and why

Abstract Even though temperate forests have lower non-native plant species richness and cover in comparison to some other habitats, such as anthropogenically influenced habitats or some grassland habitats, several recent studies from Central Europe suggest that there has been an increase in the numbers and proportions of non-native species in forests. Previous studies on the level of invasion in forest habitats were usually conducted on a relatively coarse scale, often excluding plantations of non-native trees or analyzing them together as a group regardless of the different biological properties of different species. Therefore, a more detailed analysis would be helpful to obtain better insight into the processes taking place in forests, focusing not only on the analysis of the invasion level of different forest types at a finer scale (e.g., in various types of floodplain, beech or coniferous) but also on the character of the non-native plants found there (invasive status, frequencies and habitat preferences). In this study, we aimed to (i) compare the invasion level of various forest habitats (including forests dominated by non-native trees) in Slovakia with regard to different residence times and invasive status of non-native species, (ii) analyze whether forest habitats possess specific non-native species combinations, and (iii) determine the preferences of non-native plants with respect to specific forest habitats and the co-occurrence of other plant species with the most frequent non-native species. Our study confirmed that almost all forest habitats contained at least one non-native species. Native forests at lower elevations and closer to rivers were more invaded, while broadleaved, mixed and especially coniferous forests at higher elevations and ecologically strictly limited forests were less (or un-) invaded. Significant differences between various types of riparian and coniferous forests, emphasized the importance of the more detailed discrimination of the forest habitats in comparison with previous studies. Non-native tree plantations, which are among the most invaded forests, also deserve special attention. Some non-native trees form stable communities with typical native and non-native species, where non-native dominants can act as drivers of further changes in the vegetation composition, facilitating spread of other co-occurring non-native shrubs and herbs. Taking into consideration the potential negative impacts of some non-native plants on species composition, forest microclimate and soil chemistry, it would be advisable for foresters to factor this into forest management because their choice of planted species may both positively and negatively influence the level of invasion in managed forests.

Plant community composition and structural characteristics of an invaded forest in the Galápagos

Non-native species have invaded habitats worldwide, greatly impacting the structure and function of native communities and ecosystems. To better understand mechanisms of invasion impacts and how to restore highly impacted and transformed ecosystems, studies are needed that evaluate invader effects on both biotic communities and structural characteristics. On Santa Cruz Island in Galapagos we compared biotic (plant species richness, diversity, and community composition) and structural (canopy openness, forest height, and leaf litter) characteristics of a relic forest dominated by an endemic and highly threatened tree and a forest dominated by an invasive tree. The forests are located within the historical distribution of the endemic tree, which now occupies only 1% of its original extent. We found that the invaded forest had 42% lower native plant species richness and 17% less plant diversity than the endemic tree dominated forest. Additionally, with the invader there was 36% greater non-native plant species richness, 37% higher non-native plant diversity, and highly dissimilar plant composition when compared to the endemic-dominated forest. Additionally, the invaded forest had a more open and taller tree canopy and greater leaf litter cover than native forest. The presence of the invasive tree and the associated forest structural changes were the primary factors in models that best explained higher non-native diversity in the invaded forest. Our correlational results suggest that an invasive tree has significantly altered plant assemblage and forest structural characteristics in this unique ecosystem. Experiments that remove the invader and evaluate native plant community responses are needed to identify thresholds for practical restoration of this threatened and biologically unique native forest.

Railway embankments as new habitat for pollinators in an agricultural landscape.

Pollinating insect populations, essential for maintaining wild plant diversity and agricultural productivity, rely on (semi)natural habitats. An increasing human population is encroaching upon and deteriorating pollinator habitats. Thus the population persistence of pollinating insects and their associated ecosystem services may depend upon on man-made novel habitats; however, their importance for ecosystem services is barely understood. We tested if man-made infrastructure (railway embankments) in an agricultural landscape establishes novel habitats that support large populations of pollinators (bees, butterflies, hoverflies) when compared to typical habitats for these insects, i.e., semi-natural grasslands. We also identified key environmental factors affecting the species richness and abundance of pollinators on embankments. Species richness and abundance of bees and butterflies were higher for railway embankments than for grasslands. The occurrence of bare (non-vegetated) ground on embankments positively affected bee species richness and abundance, but negatively affected butterfly populations. Species richness and abundance of butterflies positively depended on species richness of native plants on embankments, whereas bee species richness was positively affected by species richness of non-native flowering plants. The density of shrubs on embankments negatively affected the number of bee species and their abundance. Bee and hoverfly species richness were positively related to wood cover in a landscape surrounding embankments. This is the first study showing that railway embankments constitute valuable habitat for the conservation of pollinators in farmland. Specific conservation strategies involving embankments should focus on preventing habitat deterioration due to encroachment of dense shrubs and maintaining grassland vegetation with patches of bare ground.

Quantifying the landscape influence on plant invasions in Mediterranean coastal habitats

Landscape pattern might be an important determinant of non-native plant invasions because it encompasses components influencing the availability of non-native plant propagules and disturbance regimes. We aimed at exploring the relative role of patch and landscape characteristics, compared to those of habitat type and regional human influence on non-native plant species richness. For this purpose, we identified all non-native plant species in 295 patches of four coastal habitat types across three administrative regions in NE Spain differing in the degree of human influence. For each patch, we calculated several variables reflecting habitat patch geometry (size and shape), landscape composition (distribution of land-cover categories) and landscape configuration (arrangement of patches). The last two groups of variables were calculated at five different spatial extents. Landscape composition was by far the most important group of variables associated with non-native species richness. Natural areas close to diverse and urban landscapes had a high number of non-native species while surrounding agricultural areas could buffer this effect. Regional human influence was also strongly associated with non-native species richness while habitat type was the least important factor. Differences in sensitivity of landscape variables across spatial extents proved relevant, with 100 m being the most influential extent for most variables. These results suggest that landscape characteristics should be considered for performing explicit spatial risk analyses of plant invasions. Consequently, the management of invaded habitats should focus not only at the stand scale but also at the highly influential neighbouring landscape. Prior to incorporate landscape characteristics into management decisions, sensitivity analyses should be taken into account to avoid inconsistent variables.

Determinants of non-native plant species richness and composition across small Mediterranean islands

The main aim of this paper is to assess the drivers of non-native plant species richness and composition on a set of 37 small Mediterranean islands in Italy. We compiled the list of the non-native flora and distinguished species according to their establishment status. The non-native flora of the islands studied consists of 154 species, 105 of which are established on at least one island. Regression tree analysis revealed that the main determinants of both total non-native and established non-native species richness are the variables linked to tourist development and the sprawl of artificial surfaces. The variation partitioning approach shows that the variation in total non-native flora composition is driven above all by environmental variables, whereas when established taxa are considered, human-mediated factors account for most of the explained variation. Mediterranean islands have recently experienced changes in the type and intensity of human activities, leading to a decline in rural landscape and the development of tourist facilities. Our results indicate that tourism and the increase in the extension of artificial surfaces are also the main drivers of non-native plant species occurrence and establishment. These factors outweigh the effects of abiotic variables such as climate and lithology in determining the number of non-native species, whether it be total or established, as well as variations in the composition of established species. High human pressure and ornamental introductions associated with tourist activities appear to be the key elements that need to be considered when planning strategies aimed at managing plant invasions in Mediterranean islands.

Tamarisk Removal in Grand Canyon National Park: Changing the Native-Non-native Relationship as a Restoration Goal

The removal of non-native species is often an important restoration goal in natural areas, including national parks. There is often a positive correlation between non-native and native plant species richness, so that areas with the greatest number of native species support the greatest number of non-natives. This pattern may create both challenges and opportunities for restoration. Native species may be inadvertently damaged or killed during mechanical or chemical treatments targeted toward non-natives. However, greater numbers of native species may better colonize subsequent openings. We used data from an ongoing active management project in Grand Canyon National Park to test three predictions of plant community response to invasive tamarisk ( Tamarix spp.) removal. We investigated patterns of native and non-native species abundance and richness, compositional shifts, and the relationship between native and non-native species before and after treatments. In general, native species richness and abundance did not increase, but species composition following tamarisk removal tended to become more similar to that in uninvaded stands. Native and non-native species richness and abundance were positively correlated before tamarisk removal. While treatment successfully reduced cover of tamarisk after one to three years, our results suggest that it may not increase richness of native species during the same period. Furthermore, investigating native and non-native species relationships may be a useful tool for exploring hypotheses and consequences of restoration via invasive species removal.

Large Herbivore Grazing and Non-Native Plant Invasions in Montane Grasslands of Central Argentina

ABSTRACT: Grazing by large herbivores has the potential to facilitate invasion of natural grasslands by non-native plant species. Often, both herbivore identity and plant community type modulate this effect. The objective of this study was to evaluate the impact of grazing on non-native plant species richness and cover in montane grasslands of central Argentina as related to herbivore identity (horse or cattle) and plant community type. The study was conducted in piedmont valleys of the Ventania Mountains. The area is occupied by two major types of plant communities: short-needlegrass and tall-tussock grasslands. Short-needlegrass grasslands occupy poor soils and have higher plant species diversity compared to tall-tussock grasslands which typically grow on rich soils. Part of the study area is devoted to cattle husbandry, part is inhabited by feral horses, and part has been free of grazing by large herbivores for the last 15 years. We compared non-native species richness and cover at three levels of graz...

Diversity–invasibility relationships across multiple scales in disturbed forest understoreys

Non-native plant species richness may be either negatively or positively correlated with native species due to differences in resource availability, propagule pressure or the scale of vegetation sampling. We investigated the relationships between these factors and both native and non-native plant species at 12 mainland and island forested sites in southeastern Ontario, Canada. In general, the presence of non-native species was limited: <20% of all species at a site were non-native and non-native species cover was <4% m−2 at 11 of the 12 sites. Non-native species were always positively correlated with native species, regardless of spatial scale and whether islands were sampled. Additionally, islands had a greater abundance of non-native species. Non-native species richness across mainland sites was significantly negatively correlated with mean shape index, a measure of the ratio of forest edge to area, and positively correlated with the mean distance to the nearest forest patch. Other factors associated with disturbance and propagule pressure in northeastern North America forests, including human land use, white-tailed deer populations, understorey light, and soil nitrogen, did not explain non-native richness nor cover better than the null models. Our results suggest that management strategies for controlling non-native plant invasions should aim to reduce the propagule pressure associated with human activities, and maximize the connectivity of forest habitats to benefit more poorly dispersed native species.

Non-native plant invasions of United States National Parks

The United States National Park Service was created to protect and make accessible to the public the nation’s most precious natural resources and cultural features for present and future generations. However, this heritage is threatened by the invasion of non-native plants, animals, and pathogens. To evaluate the scope of invasions, the USNPS has inventoried non-native plant species in the 216 parks that have significant natural resources, documenting the identity of non-native species. We investigated relationships among non-native plant species richness, the number of threatened and endangered plant species, native species richness, latitude, elevation, park area and park corridors and vectors. Parks with many threatened and endangered plants and high native plant species richness also had high non-native plant species richness. Non-native plant species richness was correlated with number of visitors and kilometers of backcountry trails and rivers. In addition, this work reveals patterns that can be further explored empirically to understand the underlying mechanisms.

DIVERSITY–INVASIBILITY ACROSS AN EXPERIMENTAL DISTURBANCE GRADIENT IN APPALACHIAN FORESTS

Research examining the relationship between community diversity and invasions by nonnative species has raised new questions about the theory and management of biological invasions. Ecological theory predicts, and small-scale experiments confirm, lower levels of nonnative species invasion into species-rich compared to species-poor communities, but observational studies across a wider range of scales often report positive relationships between native and nonnative species richness. This paradox has been attributed to the scale dependency of diversity-invasibility relationships and to differences between experimental and observational studies. Disturbance is widely recognized as an important factor determining invasibility of communities, but few studies have investigated the relative and interactive roles of diversity and disturbance on nonnative species invasion. Here, we report how the relationship between native and nonnative plant species richness responded to an experimentally applied disturbance gradient (from no disturbance up to clearcut) in oak-dominated forests. We consider whether results are consistent with various explanations of diversity-invasibility relationships including biotic resistance, resource availability, and the potential effects of scale (1 m2 to 2 ha). We found no correlation between native and nonnative species richness before disturbance except at the largest spatial scale, but a positive relationship after disturbance across scales and levels of disturbance. Post-disturbance richness of both native and nonnative species was positively correlated with disturbance intensity and with variability of residual basal area of trees. These results suggest that more nonnative plants may invade species-rich communities compared to species-poor communities following disturbance.

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

Plant litter may play an important role in herbaceous plant communities by limiting primary production and influencing plant species richness. However, it is not known how the effect of litter interacts with fertilization. We tested for the role of litter and fertilization in a large-scale experiment to investigate effects on diversity and biomass of plant species, growth forms, native vs. non-native groups, and abiotic ecosystem components (e.g., soil moisture, PAR). We manipulated plant litter (removed vs. left in situ) and nutrient availability (NPK-fertilized vs. unfertilized) for 4 years in 314-m2 plots, replicated six times, in an old-field grassland. While many of our species-level results supported previously published studies and theory, our plant group results generally did not. Specifically, grass species richness and forb biomass was not affected by either fertilization or plant litter. Moreover, plant litter removal significantly increased non-native plant species richness. Relative to native plant species, all of our experimental manipulations significantly increased both the biomass and the species richness of non-native plant species. Thus, this grassland system was sensitive to management treatments through the facilitation of non-native plant species. We coupled biotic and abiotic components within a nonmetric multidimensional scaling (NMS) analysis to investigate treatment effects, which revealed that specific treatments altered ecosystem development. These results suggest that fertilization and plant litter may have larger impacts on plant communities and on ecosystem properties than previously understood, underscoring the need for larger-scale and longer-term experiments.

Plant Community Response to the Decline of Diffuse Knapweed in a Colorado Grassland

Long-term reductions in invasive plant species are few, and studies documenting the response of plant communities to such reductions are equally rare. We quantified plant species richness and cover during a nine-year period at a grassland site in central Colorado where the introduction of biological control insects reduced the invasive non-native forb diffuse knapweed (Centaurea diffusa). This reduction opened up 25 percent of the relative plant cover for other plant species. Based upon repeated inventories of plant species from four transects at the site we found no changes in native or nonnative plant species richness. Although we documented a modest increase from 2.4 percent to 8.6 percent in the relative cover of native forbs as knapweed declined, we observed no significant shifts in the relative cover of total native and total non-native vegetation. Two introduced grasses, field brome (Bromus arvensis [= B. japonicus]) and intermediate wheatgrass (Thinopyrum intermedium) showed significant increases. Native warm- and cool-season grasses at the site were unable to exploit the vacuum left by the decline of the knapweed. We found little evidence of native grassland restoration following the reduction of a non-indigenous, invasive plant. Our findings support the conclusion that the reduction of a regionally abundant, non-native plant species alone is not sufficient to promote restoration of the formerly dominant native plant species, and that further management activities are necessary.

RAPID ASSESSMENT OF POSTFIRE PLANT INVASIONS IN CONIFEROUS FORESTS OF THE WESTERN UNITED STATES

Fire is a natural part of most forest ecosystems in the western United States, but its effects on nonnative plant invasion have only recently been studied. Also, forest managers are engaging in fuel reduction projects to lessen fire severity, often without considering potential negative ecological consequences such as nonnative plant species introductions. Increased availability of light, nutrients, and bare ground have all been associated with high-severity fires and fuel treatments and are known to aid in the establishment of nonnative plant species. We use vegetation and environmental data collected after wildfires at seven sites in coniferous forests in the western United States to study responses of nonnative plants to wildfire. We compared burned vs. unburned plots and plots treated with mechanical thinning and/or prescribed burning vs. untreated plots for nonnative plant species richness and cover and used correlation analyses to infer the effect of abiotic site conditions on invasibility. Wildfire was responsible for significant increases in nonnative species richness and cover, and a significant decrease in native cover. Mechanical thinning and prescribed fire fuel treatments were associated with significant changes in plant species composition at some sites. Treatment effects across sites were minimal and inconclusive due to significant site and site x treatment interaction effects caused by variation between sites including differences in treatment and fire severities and initial conditions (e.g., nonnative species sources). We used canonical correspondence analysis (CCA) to determine what combinations of environmental variables best explained patterns of nonnative plant species richness and cover. Variables related to fire severity, soil nutrients, and elevation explained most of the variation in species composition. Nonnative species were generally associated with sites with higher fire severity, elevation, percentage of bare ground, and lower soil nutrient levels and lower canopy cover. Early assessments of postfire stand conditions can guide rapid responses to nonnative plant invasions.

Effects of Deer Browsing on Native and Non-native Vegetation in a Mixed Oak-Beech Forest on the Atlantic Coastal Plain

Abstract We studied the effects of browsing by Odocoileus virginianus (white-tailed deer) on the native and non-native vegetation in a mixed oak-beech forest in Rock Creek Park, Washington, DC. We compared the thickness and cover of vegetation up to 2 m in height, and species richness of native and non-native plants in 17 exclosed (1 × 4 m) and 17 control plots from 2001–2004. Over the four-year period, foraging by deer suppressed the thickness of vegetation ≤ 1 m in height, reduced the cover of herbaceous, woody, and native plants, and generally decreased the species richness of native and woody plants. Browsing had no effects on the species richness of non-native plants, but generally reduced the prevalence of Celastrus orbiculatus (oriental bittersweet). Of the dominant canopy species, browsing affected Quercus spp. (oak) regeneration, but had no apparent effects on Fagus grandifolia (American beech). These results indicate that white-tailed deer are having a detrimental effect on the structure and spe...