Conservation and land management decisions often are based primarily on natural science, but could be more successful if human influences were effectively integrated into decision making. This is especially true for efforts to manage invasive plants, whose arrival is usually the product of deliberate human introduction. Risk-assessment models that predict the probability that a nonnative plant will naturalize or invade are useful tools for managing invasive plants. However, decisions based on such models could affect stakeholders differently. Careful assessment of risk-analysis methodologies should consider the importance of stakeholder participation. We surveyed the perceptions of four stakeholder groups (conservation professionals, master gardeners, professional horticulturists, and woodland landowners) in Iowa about invasive plants, general management approaches, and risk-assessment models. We also examined whether or not a stakeholder's nature relatedness plays a role in shaping his or her responses. Stakeholder perceptions varied less than expected across all four groups. Eighty-seven percent of respondents agreed invasive plants are a problem, and 88.4% agreed that we have a responsibility to manage them to protect natural areas. Support for the use of risk-assessment models also was high, with 78.7% of respondents agreeing that their use has potential to prevent plant invasions. Nature relatedness scores for all groups were correlated with respondent perspectives on invasive plants. Respondents believed biologically significant error rates (errors that might introduce a new invasive plant) should not exceed 5 to 10%. Respondents were more tolerant of horticulturally limiting errors (errors that restrict sale/use of a plant that would not have become invasive), reporting rates of 10 to 20% as acceptable. Researchers developing risk-assessment models might wish to aim for error rates within these bounds. General agreement among these stakeholder groups suggests potential support for future risk-management efforts related to invasive plants.

Scotch broom is an invasive leguminous shrub in California and other Pacific Northwest states, as well as New Zealand and Australia. It is highly competitive in forest and shrub communities and can significantly impact reestablishment of conifer forests. The objective of this experiment was to evaluate mechanical methods (Weed Wrench, lopping), several herbicides, and herbicide application techniques for control of Scotch broom in a premontane site in California. Three herbicides were evaluated (glyphosate, imazapyr, and triclopyr ester) for canopy reduction using foliar, drizzle, and basal bark treatments. All treatments were made in both fall and late spring. In addition, we conducted a cost analysis of the various herbicide treatments and application methods. Results indicate that both mechanical treatments were effective, but their optimum timing depended on soil moisture conditions. In addition, there were no significant differences among herbicides at both timings, among all rates, and for any application method. All herbicides provided effective control of Scotch broom. However, the cost analysis demonstrated that the drizzle application method with glyphosate was the most cost-effective treatment, due to low herbicide cost and reduced labor requirements. These results provide several options for Scotch broom control and give land managers considerable flexibility with timing, herbicide, and application technique in their management programs.

Differing life histories contribute to difficulties establishing perennial grasses on lands dominated by exotic annual grasses. In a greenhouse study, we investigated to what extent allowing the perennial grass bluebunch wheatgrass to emerge before the exotic annual grass downy brome would increase its competitive ability and whether modifying nitrogen (N) would affect competition. We conducted an addition-series factorial experiment. In three cohort treatments, the two species were seeded concurrently or bluebunch wheatgrass was at the two- or four-leaf stage when downy brome was planted. N treatments were low (ambient) or high (N added to maintain 10 mg kg−1 [0.1286 oz lb−1]). Larger bluebunch wheatgrass avoided suppression by downy brome regardless of N. Under concurrent sowing, doubling downy brome density decreased bluebunch wheatgrass biomass by 22.6% ± 2.38 SE. In contrast, when bluebunch wheatgrass had a four-leaf size advantage, the same increase in downy brome density decreased bluebunch wheatgrass biomass by 4.14% ± 2.31. Larger bluebunch wheatgrass also suppressed downy brome more effectively, but N enrichment decreased the suppressive ability of bluebunch wheatgrass.

Climate change, comprising an increase in carbon dioxide levels coupled with elevated temperature, may favor invasive plants, as they possess traits that will facilitate adaptation to a new climate. In particular, alien plants of subtropical origin introduced to a colder region are expected to increase the number and size of their populations and spread farther with climate change. Seedlings of three such woody alien species in New Zealand (Archontophoenix cunninghamiana, Psidium guajava, and Schefflera actinophylla) were grown in environmental chambers under the combination of two temperature (23.7 and 26 C [74.7 and 78.8 F]) and two CO2 (450 and 900 ppmv) regimes, simulating current conditions and conditions projected for the end of the century. Total biomass of S. actinophylla was 45% higher and total leaf area 35% larger under doubled CO2 compared to current CO2. Root : shoot ratio was higher under doubled CO2 across all species, and the number of branches was increased for P. guajava. The only significant interactive effect of elevated temperature and doubled CO2 was for relative growth rate of the height of S. actinophylla seedlings. This study provides strong evidence of more vigorous growth of S. actinophylla under future conditions, particularly increased CO2, whereas the other two species appear likely to maintain current growth rates. Better knowledge of the types of future conditions that may benefit such species, together with results of species distribution models and competition and eco-physiology studies will ensure robust weed risk assessments.

Japanese barberry is an important landscape shrub that has a demonstrated potential to be invasive in ∼30 states across the central and northern United States. Forty-six cultivars were evaluated for their potential to produce fruits and seeds in a randomized, replicated field planting. Seeds from a subset of cultivars were evaluated for their ability to germinate and survive as seedlings in a deciduous woodland. Seed production for cultivars varied from no seeds to more than 12,000 seeds plant−1 and the number of seeds per fruit ranged from 0.1 to 1.8. Five cultivars produced fewer than 100 seeds plant−1, and two cultivars failed to produce fruit. When plants were allowed to mature for 4 to 5 yr beyond the first evaluation time, cultivars exhibited significant increases in fruits per plant, producing as much as 35,000 fruits plant−1 (‘Sparkle’). ‘Golden Devine’ and ‘Red Chief’, fruitless cultivars at the first evaluation, produced 165 and 20 fruit plant−1, respectively, at the follow-up evaluation, demonstrating that long-term evaluation of cultivars is necessary to accurately assess sterility. Between 12.5 and 31% cultivar seed sown in a deciduous woodland germinated, and seedlings survived at rates between 5.6 and 29.3%. Coupling cultivar seed-production data with germination and survival data in a deciduous woodland suggests that even cultivars producing as few as 100 seeds annually have the potential to contribute a few seedlings each year to a natural area.

Plant species that receive significant human introduction effort and assistance generally are the most problematic invaders. Despite this, invasive ornamental species in urban settings have received relatively little attention if not invading natural areas. Here we consider Centranthus ruber in an urban setting in South Africa as a case study and explore when emerging invaders are able to cross the urban–wildland interface and what hinders early eradication in urban environments. Centranthus ruber was introduced into Cape Town, South Africa, more than a century ago as a garden ornamental, but until recently was not considered invasive. We determine the current and potential future distribution in South Africa, evaluate current management activities, and provide recommendations for control and legislation. By August 2013, we had found 64 populations, of which 31 were casual, 27 naturalized, and 6 invasive. This increased to more than 530 identified populations by the end of 2015, due to both spread and increased awareness. Centranthus ruber can invade near-pristine areas, with one population found in natural vegetation in the Table Mountain National Park. However, with only one slowly spreading population, the threat might be limited. We found no difference in plant mortality between chemical and mechanical clearing, but with mechanical clearing stimulating the soil seedbank, we recommend chemical methods. Using a species distribution model, we found large parts of South Africa, including the southwestern Cape where we conducted our surveys, to be climatically suitable for this species. Consequently, the category 1b regional listing in NEM:BA in the Western Cape is justified, but a listing in other parts of the country also might be appropriate. Based on our findings, we suggest that the extirpation of C. ruber in South Africa is possible, but without buy-in from residents in urban environments, reinvasion will render this impossible. This study stresses the importance of managing and legislating emerging invaders at the urban–wildland interface and the monitoring of common ornamental species with invasive traits.

Integrated weed management strategies (IWM) are being advocated and employed to control invasive plants species. In this study, we compared three management strategies (biological control alone [BC], BC with fire [BC + F], and BC with mowing [BC + M]) to determine if physical controls reduce seed production by Scotch broom and interfere with the action of the biological control agent—the Scotch broom seed weevil. We measured seed production and seed predation by the weevil at both pod and plant scale, and seed bank density over two field seasons. We found no difference in the number of seeds per pod among management strategies. However, combining management strategies (BC + M and BC + F) resulted in significant reductions in pods per plant, mature seeds per plant, and seed bank density relative to biological control alone. We did not find differences among management strategies in number of weevils per pod or proportion of seeds predated by the weevil at either pod or whole-plant scale. However, combining management strategies (BC + M and BC + F) resulted in a significant reduction in healthy mature seeds per plant relative to biological control alone. Although both integrated strategies outperformed biological control alone in reducing seed production and the seed bank, with no statistical difference between them, we propose that short-rotation prescribed fire could prove to be a more effective strategy for long-term management of Scotch broom due to its potential for slightly greater depletion of the seed bank.

Garlic mustard seeds are dormant at maturity, and 90 to 105 d of cold-moist stratification at 4 C have been used to induce germination. We studied methods for breaking dormancy and inducing germination without cold stratification, for use in laboratory and greenhouse experiments with garlic mustard. Seeds were collected from large infestations, stored at room temperature, and subjected to chemical and mechanical scarification treatments. For chemical scarification, seeds were immersed in 3% (v/v) H2O2 for 12, 24, or 48 h with constant stirring, or immersed in concentrated (95 to 97%) H2SO4 for 1 or 5 min with stirring. For mechanical scarification, seeds were placed in a sandpaper-lined tumbler for 1 or 3 s. Scarified seeds, along with non-scarified seeds, were placed in petri dishes on germination blotters saturated with gibberellic acid (GA3, 10−3 M) or deionized water, and incubated for 35 d at either 20/10 C or 15/6 C (12 hr/12 hr). None of the non-scarified seeds germinated, regardless of germination solution or temperature. Seeds germinated only following scarification, and only when imbibed in GA3 solutions. Seeds immersed in H2SO4 for 5 min or mechanically scarified for 3 s had the highest level of germination in GA3. Cumulative percent germination after 35 d was greater for seeds stored 30 mo (44 to 83%), than for seeds stored 6 (2 to 60%) or 18 mo (35 to 79%), regardless of scarification treatment. The germination results, along with scanning electron micrographs of seed coats, suggest that the intact garlic mustard seed coat is permeable to water but not GA3; therefore, both scarification and GA3 are needed to break dormancy and induce germination without cold stratification.

Beach vitex is a salt-tolerant, perennial, invasive shrub that has naturalized in coastal areas of the southeastern United States. Since its introduction in the 1980s, this Pacific Rim native has invaded many fragile beach-dune ecosystems along the Mid-Atlantic, Southern Atlantic, and Gulf of Mexico. Large-scale monocultures of beach vitex supplant native species through rapid vegetative reproduction and seed production. Fruits are capable of water-based dispersal, allowing for potential rapid range expansion in coastal areas. Ecosystem damage resulting from exclusion of native plant species by beach vitex and fears associated with potential negative effects on sea turtle nesting have served to promote the control and survey efforts presently underway in coastal areas of the Carolinas, Virginia, and Maryland.

Tamarisk (a.k.a. saltcedar, Tamarix spp.) is an invasive plant species that occurs throughout western riparian and wetland ecosystems. It is implicated in alterations of ecosystem structure and function and is the subject of many local control projects, including removal using heavy equipment. We evaluated short-term vegetation responses to mechanical Tamarix spp. removal at sites ranging from 2 to 5 yr post-treatment along the Virgin River in Nevada, USA. Treatments resulted in lower density and cover (but not eradication) of Tamarix spp., increased cover of the native shrub Pluchea sericia (arrow weed), decreased density and cover of all woody species combined, increased density of both native annual forbs and the nonnative annual Salsola tragus (prickly Russian-thistle), and lower density of nonnative annual grasses. The treated plots had lower mean woody species richness, but greater herbaceous species richness and diversity. Among herbaceous species, native taxa increased in richness whereas nonnative species increased in both species richness and diversity. Thus, efforts to remove Tamarix spp. at the Virgin River reduced vegetative cover contributing to fuel loads and probability of fire, and resulted in positive effects for native plant diversity, with mixed effects on other nonnative species. However, absolute abundances of native species and species diversity were very low, suggesting that targets of restoring vegetation to pre-invasion conditions were not met. Longer evaluation periods are needed to adequately evaluate how short-term post-treatment patterns translate to long-term patterns of plant community dynamics.

The alien invasive vines black and pale swallowwort are currently spreading across eastern North America, invading parklands, old fields, restored forest sites, and other natural areas. These plants spread by wind-borne seed and can form dense stands where they become established. Although their current geographic ranges overlap, there is little known overlap locally. Preliminary observations and anecdotal information have associated black swallowwort with low-pH inceptisols and pale swallowwort with high-pH alfisols. We conducted a common garden field experiment repeated over two years and a growth chamber germination experiment to assess whether seedling emergence and performance of these two swallowworts are affected by soil type and/or soil pH. Soil pH was artificially modified. In the common garden experiment, plants of both species grown on the Onondaga County soil type (an alfisol) produced a smaller root mass than on the Orange County soil (an inceptisol). Also, in one of two years more seedlings emerged and plants produced more follicles on the Onondaga County soil. Soil pH did not affect seedling emergence, although plants grown on low pH soils had a smaller root dry mass compared with plants grown on higher pH soils. Soil pH effects on stem length, stem dry mass, and follicle production were inconsistent among years. Species differences were also evident, with more pale swallowwort seedlings emerging than black swallowwort seedlings, whereas black swallowwort plants mostly had greater biomass and fecundity than pale swallowwort plants. In the growth chamber experiment, final percentage seed germination was greater on the Onondaga County soil than on the Orange County soil. The germination speed index as well as the probability to reach 50% germination for black swallowwort was higher on the Onondaga County soil than the Orange County soil, but only at lower pH levels. The germination speed index of pale swallowwort on the Orange County soil was higher than black swallowwort at low, but not high, pH levels. In contrast, black swallowwort had a higher probability of reaching 50% germination than pale swallowwort on the Orange County soil at higher pH levels. Contrary to our expectations, interactions between the two swallowwort species with their associated soil type or with their presumably preferred soil pH were weak, contradictory, or non-existent in both experiments. This suggests that these two species can colonize and grow well in a relatively wide range of soil pH conditions. From a management perspective, our results suggest that the current range and local overlap of these two species will continue to increase and that early detection rapid response (EDRR) programs should be established in susceptible regions not yet colonized by these two invasive vines.

Riparian plant invasions can result in near-monocultures along stream and river systems, prompting management agencies to target invasive species for removal as an ecological restoration strategy. Riparian plant invaders can alter resource conditions in the benthos and drive bottom-up shifts in aquatic biota. However, the influence of management activities on the structure and function of aquatic communities is not well understood. We investigated how removal of a riparian invader, Lonicera maackii (Amur honeysuckle), influenced aquatic macroinvertebrate community functional and taxonomic diversity in a headwater stream. We hypothesized that removal of L. maackii from invaded riparia would result in (H1) increased aquatic macroinvertebrate abundance, density, and diversity; (H2) a taxonomic and functional shift in community composition; and, in particular, (H3) increased functional diversity. Aquatic macroinvertebrates were sampled monthly from autumn 2010 to winter 2013 in headwater stream riffles with a dense riparian L. maackii invasion and those where L. maackii had been experimentally removed. We found macroinvertebrate density was significantly higher in the L. maackii removal reach (P<0.05) and that macroinvertebrate community structure and functional trait presence was distinct between stream reaches and across seasons (P<0.05). The removal reach exhibited greater functional richness during spring and summer and had more unique functionally relevant taxa (20% and 85%) compared with the L. maackii reach (5% and 75%) during summer and autumn seasons. Our results suggest bottom-up processes link restoration activities in the riparian corridor and aquatic biota through alterations of functional composition in the benthic community.

On the west coast of North America and in Australia, there have been parallel cases of sequential invasion and replacement of the shoreline plant American sea-rocket by European sea-rocket. A similar pattern has also occurred in New Zealand. For 30 to 40 yr, from its first recording in 1921, American sea-rocket spread throughout the eastern coastlines of the North and South Islands of New Zealand. European sea-rocket has so far been collected only on the North Island. From its first collection in 1937, European sea-rocket spread to the northern extremity of the island by 1973, and by 2010, it had reached the southernmost limit. In the region where both species have occurred in the past, American sea-rocket is now rarely found. This appears to be another example of congeneric species displacement.

Several states in the Midwestern United States are using risk assessment to determine the invasiveness of introduced plant species, and each assessment process is different. This may lead to differences in results for the same species between states, creating concern about credibility by those using the assessments. In this study, risk assessments for six Midwestern states were compared, examining format, content, and assessment committee membership. Case studies were conducted for four species for which at least five of the six states in the study completed a risk assessment; results were compared in the context of general differences in assessment content and those specific to each species. Furthermore, 14 species for which only four of the six states completed assessments were briefly examined for outcome differences only, and possible reasons for these inconsistencies. Overall, differences in assessments did not result in incompatible conclusions for the species compared, suggesting that unique assessments in each state can provide consistent and credible results. We propose that these Midwestern states share species resources with each other to further improve consistency between the assessments.

Prediction of invasive species distributions from survey data is widely recognized as a significant component of forest management and conservation planning. Leucaena leucocephala is the most aggressive invasive shrub and tree in the Hengchun peninsula in southern Taiwan. We analyzed geo-referenced data to identify potential variables of invasion and to predict likelihood of further invasion using boosted regression trees. Our results, which classified 92% of the cells correctly with regard to species presence and absence, indicated probability of invasion is correlated with climatic conditions (temperature and precipitation), landscape features (altitude; slope ratio and aspect; percentages of natural or secondary forest, agriculture land, developed area, and water bodies; and distances to the nearest forest edge and river), and anthropogenic factors (length of forest edge, and distances to the nearest road and agriculture land). The most influential variables are average annual temperature, altitude, precipitation, and slope. Continued range expansion by L. leucocephala is most likely to proceed (1) from the eastern and western portions toward the central portion of Hengchun township and (2) throughout the southern and toward the eastern portions of Manjhou township. Our model should provide useful information to aid forest managers in the development of long term monitoring and control strategies for L. leucocephala, in the early detection and eradication of newly established invasions, and also a framework for the integration and analysis of new presence and absence field data as they become available.

Successful invasive plant eradication is rare, because the methods used target the adult stage, not taking into account the development capacity of a large seedbank. Heating by microwave was considered, because it offers a means to quickly reach the temperature required for loss of seed viability and inhibition of germination. Previous results were not encouraging, because homogeneous and deep-wave penetration was not achieved, and the various parameters that can affect treatment effectiveness were incompletely addressed. This study aimed to determine, under experimental conditions, the best microwave treatment to inhibit invasive species seed germination in terms of power (2, 4, 6 kW) and duration (2, 4, 8 min) of treatments and depending on soil moisture (10%, 13%, 20%, 30%) and seed burial depth (2, 12 cm). Three invasive species were tested: Bohemian knotweed, giant goldenrod, and jimsonweed. The most effective treatments required relatively high power and duration (2kW8min, 4kW4min, 6kW2min, and 6kW4min; 4kW8min and 6kW8min were not tested for technical reasons), and their effectiveness diminished with increasing soil moisture with germination percentage between 0% and 2% for the lowest soil moisture, 0% and 56% for intermediate soil moisture, and 27% and 68% in control treatments. For the highest soil moisture, only 2kW8min and 4kW4min reduced germination percentage between 2% and 19%. Occasionally, germination of seeds located at the 12-cm depth was more strongly affected. Giant goldenrod seeds were the most sensitive, probably due to their small size. Results are promising and justify further experiments before developing a field microwave device to treat large volumes of soil infested by invasive seed efficiently and with reasonable energy requirements. Other types of soil, in terms of texture and organic matter content, should be tested in future experiments, because these factors influence soil water content and, consequently, microwave heating.

Risk assessments of biological invasions rarely account for native species performance and community features, but the assessment presented here could provide additional insights for management aimed at decreasing vulnerability or increasing resistance of a plant community to invasions. To gather information on the drivers of native plant communities’ vulnerability and resistance to invasion, we conducted a literature search and meta-analysis. Using the data we collected, we compared native and invasive plant performance between sites with high and low levels of invasion. We then investigated conditions under which native performance increased, decreased, or did not change with respect to invasive plants. We analyzed data from 214 publications summing to 506 observations. There were six main drivers of vulnerability to invasion: disturbance, decrease in resources, increase in resources, lack of biotic resistance, lack of natural enemies, and differences in propagule availability between native and invasive species. The two mechanisms of vulnerability to invasion associated with a strong decline in native plant performance were propagule availability and lack of biotic resistance. Native plants marginally benefited from enemy release and from decreases in resources, while invasive plants strongly benefited from both increased resources and lack of enemies. Fluctuation of resources, decreases and increases, were strongly associated with higher invasive performance, while native plants varied in their responses. These differences were particularly strong in instances of decreasing water or nutrients and of increasing light and nutrients. We found overall neutral to positive responses of native plant communities to disturbance, but natives were outperformed by invasive species when disturbance was caused by human activities. We identified ecosystem features associated with both vulnerability and resistance to invasion, then used our results to inform management aimed at protecting the native community.

Common reed (Phragmites australis) is a nonnative invasive perennial grass that is problematic in aquatic and riparian environments across the United States. Common reed often forms monotypic stands that displace native vegetation which provide food and cover for wildlife. To help maintain native habitats and manage populations of common reed in the United States, an understanding of its life history and starch allocation patterns are needed. Monthly biomass samples were harvested from sites throughout the Mobile River delta in southern Alabama, USA from January 2006 to December 2007 to quantify seasonal biomass and starch allocation patterns. Total biomass of common reed throughout the study was between 1375 and 3718 g m−2 depending on the season. Maximum aboveground biomass was 2200 ± 220 g m−2 in October of 2006 and 1302 ± 88 g m−2 in December of 2007. Maximum belowground biomass was seen in November of 2006 and 2007 with 1602 ± 233 and 1610 ± 517 g m−2 respectively. Biomass was related to ambient temperature, in that, as temperature decreased aboveground biomass (p = 0.05) decreased. Decreases in aboveground biomass were followed by an increase in belowground biomass (p < 0.01). Starch comprised 1 to 10% of aboveground biomass with peak temporary storage occurring in July and August 2006 and September to November of 2007. Belowground tissues stored the majority of starch for common reed regardless of the time of year. Overall, belowground tissues stored 5 to 20% of total starch for common reed with peak storage occurring in December 2006 and October 2007. Starch allocation to belowground tissues increased as temperatures decreased. Understanding seasonal life history patterns can provide information to guide management strategies by identifying the vulnerable points in biomass and starch reserves in common reed.

Understanding competition for soil nitrate between common shrub-steppe, potential reclamation species, and common invasive species is necessary to identify mechanisms associated with ecosystem invasion and can assist with developing weed management scenarios. We designed a field experiment to evaluate the differential competitive effects of the invasive annual grass downy brome, the invasive biennial forb dyer's woad, and the reclamation shrub prostrate kochia, on nitrate acquisition of the perennial grass crested wheatgrass, the native forb western yarrow, and the native shrub big sagebrush. Individual plants were grown in two-plant neighborhoods, and a K15NO3 tracer was injected into the soil between plants and recovered from leaf material after 5 to 11 d. We also evaluated neighbor effects on shoot and root growth, leaf carbon : nitrogen ratio, and leaf nitrogen concentrations to better understand how these traits are associated with differences in nitrate acquisition and nitrogen allocation among the three growth forms. Nitrate acquisitions by crested wheatgrass and western yarrow were significantly lower when competing with downy brome than with dyer's woad and prostrate kochia; however, competitors had similar, negative effects on nitrate acquisition by big sagebrush. Nitrate acquisition ratios between competing neighbors revealed that: (1) the grasses always acquired more nitrate than neighbors of a different growth form, (2) western yarrow was equally competitive with dyer's woad and prostrate kochia, and (3) all neighbors acquired more nitrate than big sagebrush. More successful competition for nitrate in the grasses was associated with greater specific root length. Compared to species of the same respective growth form, the two invasive weeds (downy brome and dyer's woad) and prostrate kochia always had significantly lower leaf carbon : nitrogen ratio, and greater leaf nitrogen concentration, which have been broadly correlated with leaf lifespan and nutrient use efficiency, and indicate differing strategies to persist in the semiarid shrub-steppe ecosystems.

Invasion of closed canopy forests by shade-tolerant alien plants has the potential to modify species composition, stand structure, ecosystem function, and long-term forest development patterns. Ligustrum sinense is a shade-tolerant alien shrub that has invaded bottomland forests throughout the southeastern United States. This species has received comparatively little attention in the literature despite its potential to drastically alter invaded sites. The overarching goal of our study was to document the relationships between Ligustrum sinense invasion and woody plant biodiversity and development patterns in an intact southeastern U.S. bottomland forest. The forest was dominated by Quercus nigra and Liquidambar styraciflua. Ligustrum sinense ranked fifth in basal area contribution, occurred in 97% of our plots, and represented 95% of all understory stems. Spearman's rho for dominance (based on basal area of stems > 5 cm diameter at breast height [dbh]) of L. sinense and woody plant species richness for each plot revealed a significant negative relationship (rs = −0.69, P < 0.01). A similar relationship was revealed between L. sinense density and woody plant species diversity (rs = −0.78, P < 0.01) and evenness (rs = −0.82, P < 0.01). Spearman's rho for L. sinense density and native understory stem density (individuals ≥ 1 m height, < 5 cm dbh) also revealed a significant negative association (rs = −0.48, P < 0.01). Under the current disturbance regime and without active management, we projected the forest would shift to support a stronger component of L. sinense and that structure would transition from tree to shrub dominance for sites within the forest.