The relationship between plant community composition and invasibility has been studied extensively but seldom in the context of ecosystem restoration. Experimental riparian restoration plots differing in species composition and density were established and evaluated for susceptibility to invasion by giant reed, a common riparian invader in California, and natural recruitment by riparian species over time. Plots were planted in 2002 with cuttings of common threesquare (a sedge), seepwillow (a shrub), and Goodding's willow (a tree) at two densities in monoculture and all possible mixture combinations. Giant reed rhizomes were introduced into half of the plots in the spring of 2003, while the remaining plots were allowed to undergo natural recruitment for an additional year. In late winter 2004, giant reed rhizomes were planted in the remaining plots. Both planting groups were followed for one growing season to evaluate giant reed establishment, survival, and growth. Community composition affected giant reed performance, particularly in 2003 before natural recruitment occurred. In that year, plots containing seepwillow + willow had the lowest giant reed shoot production, growth, and survival. All plots containing seepwillow were resistant to colonization by natural recruitment in 2004, but none of the planting treatments affected giant reed success in that year. Giant reed was more successful overall in 2004 despite deeper shade and drier soils. This pattern could be attributed to larger initial rhizome size in 2004, which allowed giant reed to overcome environmental stress during establishment. Planting density did not impact giant reed or natural recruitment independently, but may affect environmental parameters and warrants further study as a potential contributor to restoration success. Our results indicate that choice of species composition in restoration might impact giant reed invasion success initially, but community resistance might not be sustainable and maintenance-free over time.

Few individuals or governments have suggested that invasions by nonindigenous species are relevant to the broader issue of human security, despite a growing awareness of the ecological, economic, and societal impacts associated with invasive nonindigenous species (INIS). We propose that by framing management actions in a human and environmental security context, the threats (and benefits) posed by INIS to individuals and communities can be explicitly articulated and debated. This framework allows multiple stakeholders to bring their concerns to bear upon specific policy, and attempts to integrate broad environmental concerns within its parameters. We use the case of ecosystem-based management of invasive nonindigenous plants as an example of the utility of a human security framework. The dominant management approach to these species remains focused on the individual species, despite increasing calls for the implementation of ecosystem-based management strategies. Ecosystem-based management is supported by generalized and widely accepted mechanisms of plant community dynamics, such as succession, disturbance, and interspecific competition, but these scientific arguments do not consistently carry weight at the policy level and with the broader public. A human security framework may provide an approach for overcoming this resistance by placing the debate over management within the social and political context of the wider community. Overall, human security can allow applied ecologists to be better positioned to meet the challenges of communicating the need for science-based management.

Chinese privet is a major invasive shrub within riparian zones throughout the southeastern United States. We removed privet shrubs from four riparian forests in October 2005 with a Gyrotrac® mulching machine or by hand-felling with chainsaws and machetes to determine how well these treatments controlled privet and how they affected plant community recovery. One year after shrub removal a foliar application of 2% glyphosate was applied to privet remaining in the herbaceous layer. Three “desired-future-condition” plots were also measured to assess how well treatments shifted plant communities toward a desirable outcome. Both methods completely removed privet from the shrub layer without reducing nonprivet shrub cover and diversity below levels on the untreated control plots. Nonprivet plant cover on the mulched plots was > 60% by 2007, similar to the desired-future-condition plots and higher than the hand-felling plots. Both treatments resulted in higher nonprivet plant cover than the untreated controls. Ordination showed that after 2 yr privet removal plots were tightly grouped, suggesting that the two removal techniques resulted in the same plant communities, which were distinctly different from both the untreated controls and the desired-future-condition. Both treatments created open streamside forests usable for recreation and other human activities. However, much longer periods of time or active management of the understory plant communities, or both, will be required to change the forests to typical mature forest plant communities.

The distribution and abundance of invasive species can be strongly influenced by habitat suitability and by corridors that facilitate dispersal. We synthesize results from a large-scale invasive plant survey with a patch-scale expansion experiment. The large-scale survey involved transects up to 250 m away from of all roads in a 32,000 ha forest. The patch experiment involved initiating invasions in different habitat types (roadside, wetland, disturbed, and intact forests), and then fitting statistical models to patch spread rates. The large-scale survey highlighted the importance of roads in predicting the presence of invasive plants, also revealing that one invasive plant, Microstegium vimineum, has spread rapidly since its purported introduction in 1994. The patch-scale experiments focused on Microstegium and demonstrated that spread rates are higher in roadsides than in forested and wetland patches, even in the absence of major disturbances. These results highlight the importance of landscape features when designing prevention and management practices aimed at limiting invasive plant abundance and spread.

The herbicide imazapic is registered for use on rangelands and provides effective short-term control of certain invasive annual grasses. However, details about optimal application rates for downy brome and susceptibility of simultaneously seeded species are lacking. Thus, we investigated downy brome and seeded species responses to variable rates of imazapic (0, 35, 70, 105, and 140 g ai/ha) in two plant communities (salt desert shrub and Wyoming big sagebrush). In autumn 2003, plots were treated with imazapic and seeded with one of five perennial plant materials (Siberian wheatgrass [‘Vavilov’ and the experimental source Kazak]; prostrate kochia [‘Immigrant’ and the experimental source 6X], and Russian wildrye [‘Bozoisky II’]). Downy brome cover and seeded species establishment were evaluated in spring 2004 and 2006. Downy brome cover in 2004 decreased with increasing imazapic rate at both sites, although more so at the Wyoming big sagebrush site. In 2006, no difference in downy brome cover existed among herbicide rates at the Wyoming big sagebrush site. At the salt desert shrub site, the high rate of imazapic reduced downy brome cover by about 25% compared to untreated plots. ‘Vavilov’ Siberian wheatgrass was the only seeded species with lower downy brome cover in 2006 than 2004. Seeded species establishment increased with imazapic rate in the salt desert shrub community, but in the Wyoming big sagebrush community it peaked at intermediate rates and declined at higher rates. Variation in downy brome control and seeded species establishment might have been associated with differences in precipitation, soil organic matter, and disturbance history between sites. Overall, imazapic was useful for helping establish desirable perennial species, but unless downy brome is reduced below a critical threshold, favorable precipitation can return sites to pretreatment levels within two years.

Many land managers are faced with trying to optimize management of invasive plant species based on budget constraints and lack of knowledge of the true potential of the species. Generally, “early detection rapid response” (EDRR) is the assumed best management strategy and tends to drive management regardless of the invasion stage or possible variation in the invasion potential of the population. We created a simulation model to evaluate the optimal management strategy to reduce the rate of invasion of nonindigenous plant species. The strategies were specifically chosen to assess the value of information from monitoring populations. We compared four management strategies and a no-management control over a 20-yr period in the context of a management area: (1) managing a fixed number of populations at random each year (EDRR random), (2) managing an equivalent number of populations along a road each year (EDRR road), (3) managing half of the fixed populations that were determined by monitoring to be sources of new populations (monitoring every year), and (4) managing an equivalent set of source populations only on even years, leaving the odd years for monitoring (monitoring every other year). EDRR random location without regard to population invasion potential, and monitoring every year targeting management on populations determined to be invasive (sources for new populations), were the most successful strategies for reducing the increase in total number of populations. The model simulations suggest that managers could dedicate 50% of their management time to monitoring without risk of accelerating invasions or reducing the impact of their weed management program.

Heterogeneity in disturbance regimes, propagule pools, and factors affecting plant performance are a ubiquitous feature of wildlands. We tested a conceptual framework, termed augmentative restoration, aimed at identifying and selectively repairing or replacing damaged processes based on their predicted influence on the three causes of succession: site availability, species availability, and species performance. This framework was tested at three sites each with a different cause of succession naturally occurring in an ephemeral wetland dominated by invasive plants that had varying levels of disturbance (site availability), remnant native plants (species availability), and water availability (species performance). Our hypotheses were (1) seeding combined with watering would augment meadow vole disturbance to increase desired species composition, (2) shallow tilling combined with watering would augment remnant native species, and (3) shallow tilling combined with seeding would augment mesic soils to increase desired species composition. Shallow tilling, watering, and seeding were applied in a factorial arrangement at all three sites. These eight treatment combinations were applied in a split-plot design with four replications to generate 32 whole plots (2 m2). The herbicide 2,4-D was applied on half of each whole plot to influence relative species performance. In two of the three sites, using augmentative restoration to guide our management approaches improved our decision as to the treatment combinations that would maximize seedling establishment. Selectively augmenting successional processes that remain intact by repairing or replacing processes occurring at inadequate levels can improve implementation of successional management and provide a refined process-based framework for restoration across heterogeneous landscapes. Besides the clear economic advantages of lower management inputs associated with augmentative restoration, avoiding unnecessary management inputs has the additional advantage of minimizing unintended negative impacts on ecosystem processes.

Tamarisk species are shrubs or small trees considered by some to be among the most aggressively invasive and potentially detrimental exotic plants in the United States. Although extensively studied in the southern and interior west, northwestern (Oregon, Washington, and Idaho) distribution and habitat information for tamarisk is either limited or lacking. We obtained distribution data for the northwest, developed a habitat suitability map, and projected changes in habitat due to climate change in a smaller case study area using downscaled climate data. Results show extensive populations of tamarisk east of the Cascade Mountains. Despite the perceived novelty of tamarisk in the region, naturalized populations were present by the 1920s. Major population centers are limited to the warmest and driest environments in the central Snake River Plain, Columbia Plateau, and Northern Basin and Range. Habitat suitability model results indicate that 21% of the region supports suitable tamarisk habitat. Less than 1% of these areas are occupied by tamarisk; the remainder is highly vulnerable to invasion. Although considerable uncertainty exists regarding future climate change, we project a 2- to 10-fold increase in highly suitable tamarisk habitat by the end of the century. Our habitat suitability maps can be used in “what if” exercises as part of planning, detection, restoration, management, and eradication purposes.

Chemical, mechanical, and biological methods are used to manage invasive plants, but their effectiveness at removing specific plant invaders while preserving native communities varies widely. Chemical methods are used most extensively but the nontarget effects of some herbicides can have lasting effects on native plants. Nonchemical methods are needed for sites containing rare or threatened native species and where the cost of herbicides is prohibitive. Here we evaluate multiple nonchemical methods for removing Japanese stiltgrass, a nonnative annual grass that is rapidly invading eastern U.S. forests. We applied mowing, hand weeding, and spring and fall fire treatments to replicated plots at three forested sites in southern Indiana and compared the response of Japanese stiltgrass and native plants to untreated reference plots. Mowing and fall fires applied just before seed set were the most effective methods for removing Japanese stiltgrass. Mowing decreased invader cover by 70% and biomass by 95%, whereas fall fires reduced cover by 79% and biomass by 90% compared to reference plots. Spring fire reduced Japanese stiltgrass cover, but not biomass, and hand weeding did not significantly reduce invader cover or biomass compared to untreated plots. There were no significant differences in the response of the overall native plant community or of specific native plant functional groups to the removal treatments. In summary, mowing and properly timed fall fires may be effective nonchemical methods for managing Japanese stiltgrass invasions and restoring native communities. Future research should focus on evaluating the responses of Japanese stiltgrass, native species, and other plant invaders to removal treatments conducted over successive growing seasons across a range of invaded habitats.

Total nonstructural carbohydrate (TNC) reserves support growth, formation of reproductive structures, and sprouting of plant tissues, and nitrogen (N) is essential for amino acid synthesis and photosynthetic enzyme production. Timing of weed management to periods when these critical resources are most limiting might improve efficacy. We examined seasonal changes in carbohydrate and nitrogen concentrations in Brazilian egeria (Egeria densa), a common submersed aquatic weed, from two locations in the United States. Plants were collected from a coastal Oregon reservoir and from California's Central Valley in the Sacramento–San Joaquin Delta. Starch comprised between 35 to 51% of the TNC in lower stems and root crowns. Seasonal changes in resource concentrations were not consistent between years within a population or for the same plant part between different populations. Lowest TNC concentrations were observed earlier in the growing season (March) in Disappointment Slough than in Big Creek (May to June). Conversely, highest concentrations were observed in October in Disappointment Sough and from August to March in Big Creek. Nitrogen concentrations were highest in stem tips in both populations, with more distinct seasonal changes in the California population. These data suggest western populations of E. densa might exhibit less-discernible low points in root crown and lower stem energy storage for targeting management activities to vulnerable phenological stages. Brazilian egeria has high phenological plasticity despite its low genetic diversity and lack of specialized reproductive and perennating structures, which allows the plant to invade and dominate submersed plant communities in areas with mild winters.

Since the 1950s, many south Texas rangelands have been seeded with buffelgrass, a perennial C4 bunchgrass native to Africa that is believed to contribute to reductions in biodiversity. Forb species represent a critical habitat component throughout the breeding period for many wildlife species as seed (summer to fall), as green vegetative material (spring to summer), and as habitat for arthropods (spring to summer). Reductions in richness and diversity of crucial ecosystem components such as forbs and arthropods have large implications for grassland birds and other wildlife. We sampled annual and perennial forbs within 1-m2 quadrats on 15 study plots (1 ha; n = 20 quadrats/plot) at Chaparral Wildlife Management Area, in LaSalle and Dimmit counties, Texas, during 2005 and 2006. Study plots were divided into five light-buffelgrass plots (0 to 5% buffelgrass canopy coverage), five moderate-buffelgrass plots (5 to 25% buffelgrass canopy coverage), and five heavy-buffelgrass plots (> 25% buffelgrass canopy coverage). Buffelgrass in study plots was composed of naturalized plants, and was not deliberately planted. During 2005 we observed that plots with > 25% buffelgrass had a 73% reduction in forb canopy of native species, a 64% reduction in native forb species richness, and a 77% reduction in native forb stem density compared to plots with 0 to 5% buffelgrass. These trends in native forb reduction (−79% native forb canopy, −65% forb species richness, −80% forb stem density) were nearly identical in 2006, even with greatly reduced rainfall. Simple linear regression revealed negative relationships between buffelgrass cover, total exotic grass cover (buffelgrass and Lehmann lovegrass), and total grass cover and the richness, coverage, and density of forbs/m2. Reductions in diversity may have larger implications regarding ecosystem function and available useable space and densities of desired bird species such as northern bobwhite.

Invasive aquatic weeds negatively affect biodiversity, fluvial dynamics, water quality, and water storage and conveyance for a variety of human resource demands. In California's Sacramento–San Joaquin River Delta, one submersed species—Brazilian egeria—and one floating species—waterhyacinth—are actively managed to maintain navigable waterways. We monitored the spatial and temporal dynamics of these species and their communities in the Sacramento-San Joaquin River Delta using airborne hyperspectral data and assessed the effect of herbicide treatments used to manage these species from 2003 to 2007. Each year, submersed aquatic plant species occupied about 12% of the surface area of the Delta in early summer and floating invasive plant species occupied 2 to 3%. Since 2003, the coverage of submersed aquatic plants expanded about 500 ha, whereas the coverage of waterhyacinth was reduced. Although local treatments have reduced the coverage of submersed aquatic plants, Delta-wide cover has not been significantly reduced. Locally, multiyear treatments could decrease submersed aquatic plants spread, given that no residual plants outside the treated area were present. In contrast, the spread of waterhyacinth either has been constant or has decreased over time. These results show that (1) the objectives of the Egeria densa Control Program (EDCP) have been hindered until 2007 by restrictions imposed on the timing of herbicide applications; (2) submersed aquatic plants appeared to function as ecosystem engineers by enabling spread to adjacent areas typically subject to scouring action; (3) repeated herbicide treatment of waterhyacinth has resulted in control of the spread of this species, which also appears to have facilitated the spread of waterprimrose and floating pennywort. These results suggest that management of the Delta aquatic macrophytes may benefit by an ecosystem-level implementation of an Integrated Delta Vegetation Management and Monitoring Program, rather than targeting only two problematic species.

Water use by saltcedar, an invasive phreatophyte, is of significant concern in many riparian zones in the western United States. Diurnal groundwater fluctuations were analyzed to estimate evapotranspiration and water salvage (water available for other ecological functions) in saltcedar stands over a 6-yr period on a site along the Pecos River in Texas. Seasonal stand-level saltcedar water loss at an untreated control site ranged from 0.42 to 1.18 m/yr. Seasonal water salvage following application of imazapyr ranged from 31% 4 yr after treatment to 82% 2 yr after treatment. Significant water savings may be achieved by chemical saltcedar control, dependent upon water use by replacement vegetation and saltcedar regrowth. A regrowth management strategy is essential to maintain long-term water salvage.

Sulfur cinquefoil, a perennial invasive weed of many different habitats in the United States, reproduces and spreads predominately through seed production, making seed bank survival and successful germination essential steps in the invasive process. To evaluate its potential to invade water-stressed environments, field and growth chamber studies were conducted in two areas of sulfur cinquefoil seed ecology: (1) monitoring the seed bank population and (2) determining the effect of salt and water stresses on germination of two sulfur cinquefoil seed populations differing in site characteristics of precipitation, temperature, and soil conditions. Field sampling demonstrated that a 2-yr average seed rain of 73,700 seeds m−2 resulted in an average 26,600 seeds m−2 annual increase in the seed bank. Regression analysis showed seed rain accounted for only 7 and < 1% of the variation in seedling density in 2003 and 2004, respectively. Seeds from the two populations showed a difference in the level of decrease in germination in response to increasing water and salt stresses. Managers should be aware that some populations of sulfur cinquefoil may be able to survive under drier or saltier conditions than previously thought. It appears that several years of control of mature sulfur cinquefoil would dramatically reduce the sulfur cinquefoil seed bank.

Seed persistence is poorly quantified for invasive plants of subtropical and tropical environments and Lantana camara, one of the world's worst weeds, is no exception. We investigated germination, seedling emergence, and seed survival of two lantana biotypes (Pink and pink-edged red [PER]) in southeastern Queensland, Australia. Controlled experiments were undertaken in 2002 and repeated in 2004, with treatments comprising two differing environmental regimes (irrigated and natural rainfall) and sowing depths (0 and 2 cm). Seed survival and seedling emergence were significantly affected by all factors (time, biotype, environment, sowing depth, and cohort) (P < 0.001). Seed dormancy varied with treatment (environment, sowing depth, biotype, and cohort) (P < 0.001), but declined rapidly after 6 mo. Significant differential responses by the two biotypes to sowing depth and environment were detected for both seed survival and seedling emergence (P < 0.001). Seed mass was consistently lower in the PER biotype at the population level (P < 0.001), but this variation did not adequately explain the differential responses. Moreover, under natural rainfall the magnitude of the biotype effect was unlikely to result in ecologically significant differences. Seed survival after 36 mo under natural rainfall ranged from 6.8 to 21.3%. Best fit regression analysis of the decline in seed survival over time yielded a five-parameter exponential decay model with a lower asymptote approaching −0.38 (% seed survival = [(55 − (−0.38)) · e (k · t)] + −0.38; R 2 = 88.5%; 9 df). Environmental conditions and burial affected the slope parameter or k value significantly (P < 0.01). Seed survival projections from the model were greatest for buried seeds under natural rainfall (11 yr) and least under irrigation (3 yr). Experimental data and model projections suggest that lantana has a persistent seed bank and this should be considered in management programs, particularly those aimed at eradication.

Broom snakeweed is one of the most widespread range weeds in western North America. Although a native plant, it increases with disturbance such as overgrazing, fire, and drought, and can dominate sites. The objective of this study was to test the hypothesis that defoliation of broom snakeweed alone, and along with associated grasses, would reduce its vigor and increase its mortality in bunchgrass plant communities. The study was conducted at two locations: near Nephi, UT in an invaded crested wheatgrass stand and at Howell, UT in a bluebunch wheatgrass/Wyoming big sagebrush community. Clipping treatments consisted of (1) untreated Control; (2) All Clip—clipping all herbaceous vegetation 2 cm above the soil surface, and current season foliar growth of snakeweed; (3) Grass Clip—clipping all grass and forb plants; (4) Snakeweed Clip—clipping current season foliar growth. Treatments were randomly assigned to 1-m2 plots and clipped in May or late August. Plots were measured and clipped at the respective seasons annually from 2004 to 2007. Defoliation of snakeweed in spring in the Snakeweed Clip treatment caused higher mortality and lower size and vigor of remaining plants than the other treatments at the end of the study. Clipping all vegetation also reduced snakeweed density at Nephi, but not at Howell. There was little regrowth of bluebunch wheatgrass at Howell in the All Clip treatment; thus, it was likely to have not competed with snakeweed regrowth for limited soil moisture. Bluebunch wheatgrass cover declined at Howell in the All and Grass Clip treatments. Crested wheatgrass was not adversely affected by spring defoliation in the All and Grass Clip treatments, and it increased in the Snakeweed Clip treatment. There were few differences in the fall defoliations. Spring defoliation of snakeweed put it at a competitive disadvantage with both intact perennial bunchgrasses and regrowth crested wheatgrass, thus enhancing its mortality.

Diflufenzopyr is a synergist that improves broadleaf weed control when mixed with certain auxinic herbicides. In nonagricultural settings, it is only available in a premix with dicamba, which is labeled for noncrop sites, pasture, hay, and rangeland. Our objectives were to determine the influence of diflufenzopyr + dicamba when applied with auxinic herbicides for Russian knapweed control. Studies were conducted near Ethete, WY, from 2005 to 2008 in a pasture heavily infested with Russian knapweed. Treatments were applied in the fall (September) and included aminopyralid, clopyralid, clopyralid + 2,4-D, clopyralid + triclopyr, and picloram at standard and reduced rates, with and without diflufenzopyr + dicamba. At 12 and at 24 mo after treatment (MAT), diflufenzopyr + dicamba did not influence Russian knapweed control when applied with standard rates of aminopyralid, clopyralid, clopyralid + 2,4-D, clopyralid + triclopyr, or picloram. All of these treatments except clopyralid + 2,4-D consistently provided ≥ 80% control 24 MAT. Reduced-rate herbicide interactions with diflufenzopyr + dicamba were also not significant at 12 MAT. However, at 24 MAT, aminopyralid applied with diflufenzopyr + dicamba controlled Russian knapweed 83% compared with 59% when aminopyralid was applied alone. Russian knapweed control with all other reduced-rate treatments, except picloram, fell below 80%. These results indicate that diflufenzopyr + dicamba does not generally improve Russian knapweed control at 12 or 24 MAT with either standard or reduced rates of typical fall, auxinic herbicide treatments.

We used a growth chamber experiment with first-year garlic mustard plants to explore the effects of three garlic mustard removal techniques (treatment with glyphosate, pulling out the entire plant, and clipping the shoot) on growth of the native herb pale jewelweed and its associated mycorrhizal fungi. We also explored the effects of activated carbon and mycorrhizal inocula amendments. We monitored plant height, intra- and extraradical mycorrhizal structures, root growth, and the fractal dimension of the root system. Removing as much garlic mustard root tissue as possible by hand pulling plants led to larger jewelweed plants than other removal methods. Activated carbon and mycorrhizal inocula did not improve plant growth.