Russian-olive is a small tree or large multistemmed shrub that was introduced to Canada and the United States from Eurasia in the early 1900s. It was provisioned in large numbers during the last century to prairie farmers as a shelterbelt plant and remains a popular and widely available ornamental. Now invasive within some riparian ecosystems in the western United States, Russian-olive has been declared noxious in the states of Colorado and New Mexico. With traits including high shade tolerance and a symbiotic association with nitrogen-fixing bacteria, Russian-olive has the potential to dominate riparian vegetation and thus radically transform riparian ecosystems. Especially alarming is its capacity to influence nutrient dynamics within aquatic food webs. Our objective is to draw attention to Russian-olive as a potential threat to riparian ecosystems within Canada, especially in the southwest, where invasion is becoming commonplace. We review what is known about its biology and about the threats it poses to native organisms and ecosystems, and we summarize management and control efforts that are currently underway. We conclude by proposing a research agenda aimed at clarifying whether and how Russian-olive poses a threat to riparian ecosystems within western Canada.

Nomenclature: Russian-olive; Elaeagnus angustifolia L. ELGAN.

Introduced accidentally from South America, deeproot sedge is rapidly expanding in a variety of habitats throughout the southeastern United States. Of particular concern is its rapid expansion, naturalization, and formation of monocultures in Texas coastal prairie, one of the most imperiled temperate ecoregions in North America. The objective of this research was to examine how deeproot sedge responds to prescribed fire, to the herbicide imazapic, and to treatment combinations of both. Combinations of prescribed fire and imazapic treatments and imazapic-only treatments effectively reduced deeproot sedge cover and frequency. However, plots exposed to dormant season fires (with no imazapic) had greater deeproot sedge cover after burn treatments were applied, indicating that coastal prairie management using only dormant season prescribed fire will not work toward reduction or management of this exotic invasive species. Although deeproot sedge cover was often reduced in fire–imazapic treatment combinations, it was still present in treatment plots. Moreover, desirable functional plant groups (i.e., native bunchgrasses) did not respond positively to the fire–imazapic treatments, but in some instances, woody plant coverage increased. Repeated, long-term approaches using integrated and coordinated efforts with multiple treatment options will be necessary to restore community structure to desired compositional levels. Such integrated approaches should be effective in reducing deeproot sedge frequency, cover, and extent to more manageable levels throughout its introduced geographic range.

Nomenclature: Imazapic; deeproot sedge; Cyperus entrerianus Boeck.

Management Implications: This research is the first attempt, to our knowledge, to quantify the utility of prescribed fire, herbicide, and combinations thereof, to control deeproot sedge in coastal prairie. Prescribed fire alone, particularly during the time when most prescribed fires are performed (winter), did not work to reduce deeproot sedge cover or frequency. Specifically, combining imazapic and prescribed fire, with a long-term management goal of reimplementation of growing-season prescribed fire, should reduce deeproot sedge cover and frequency. Imazapic application can be effective throughout the growing season, both alone and in combination with prescribed fire, in reducing both the extent and the frequency of deeproot sedge. Both long- and short-term control will be dependent on effective monitoring of both aboveground plant and seed-bank response. As deeproot sedge produces a tremendous biomass (kg ha⁻¹) of highly germinable seeds, seed bank management will remain a key element in restoration of invaded sites. This research provides some of the first evidence that deeproot sedge control may be achieved through integrated management with both imazapic and prescribed fire.

Nonnative invasive plants (NNIP) have far-reaching effects on native ecosystems worldwide. Understanding the role of generalist seed dispersers in spreading NNIP across the landscape is important to the conservation of native ecosystems and to the management of NNIP. We studied white-tailed deer (Odocoileus virginianus) as a seed disperser in a mixed maritime pine (Pinus spp.) forests on Parris Island, SC, with particular interest in the dispersal of Chinese tallowtree [Triadica sebifera (L.) Small], a highly invasive tree species in the southeastern United States, which is a management concern on Parris Island, SC. We collected deer scat pellet groups along transects in two forest types: those that had recently been treated with silvicultural timber harvest (thinned) and those that have not been so treated (unthinned). Using two pellet-treatment methods, directly planting or rinsing and sorting, we determined that, out of 25 species grown under greenhouse conditions, 28% (n  =  7) were nonnative, small-seeded, herbaceous species. However, T. sebifera was not identified in either of the two treatment methods. Recent forest thinning significantly affected the number of species determined in deer pellet groups (F  =  8.37; df  =  1; P < 0.01), with more native plant species identified in unthinned (x̄  =  25 ± 11) than in thinned (x̄  =  3 ± 10) forest stands (F  =  5.33; df  =  1; P  =  0.02). Our results indicate that white-tailed deer are actively dispersing nonnative seeds but not those of T. sebifera or other woody NNIP.

Nomenclature: Chinese tallowtree; Triadica sebifera (L.) Small; pine; Pinus spp.; white-tailed deer; Odocoileus virginianus.

Management Implications: Our study investigated whether white-tailed deer (Odocoiles virginianus) were active dispersers of Chinese tallowtree (Triadica sebifera) and other nonnative invasive plants (NNIP) in mixed maritime pine (Pinus spp.) forests at Parris Island Marine Corps Recruit Depot (MCRD), Parris Island, SC. Dispersal by generalist herbivores can lead to the establishment of NNIP in new, potentially uninvaded locations resulting in changes in ecological trajectories that can directly affect management activities. We determined that white-tailed deer were not dispersing T. sebifera but were active dispersers of other nonnative plants. White-tailed deer are ubiquitous, generalist herbivores that are overabundant in many areas of the eastern United States. When overabundant, or when native plant resources are lacking during periods of nutritional stress, white-tailed deer will alter their forage choices and select alternative plant species. Forest management activities (i.e., timber harvesting operations, prescribed burning, etc.) may provide the necessary conditions for nonnative plant establishment through increased solar radiation and mineral soil exposure and should be considered if mitigating invasive species spread.

The expansion of populations of invasive species continues to compromise the ecological and economic integrity of our natural resources. The negative effects of invasive species on native biota are widely reported. However, less is known about how the duration (i.e., age of oldest invaders) and intensity (i.e., density and percent cover) of an invasion influences native plant diversity and abundance at the microsite scale. We examined the influence of density, percent cover, and age of Amur honeysuckle (a nonnative invasive shrub), and several environmental factors on native plant taxa at 12 mixed hardwood forests in Indiana, USA. Overall, study sites with the greatest taxonomic diversity (Shannon's Diversity; H′), richness (S), percent cover, and density of native vegetation also had the lowest percent cover of Amur honeysuckle in the upper vertical stratum (1.01 to 5 m). Based on linear mixed model analyses, percent cover of Amur honeysuckle in the upper vertical stratum was consistently and negatively correlated with H′, S, total percent cover, and woody seedling density of native taxa at the microsite scale (P < 0.05). Duration of Amur honeysuckle at the microsite scale was not significant when percent cover of Amur honeysuckle in the upper vertical stratum was included in models. However, duration of Amur honeysuckle invasion was significantly correlated with dependent variables and with upper-stratum honeysuckle cover, suggesting that older Amur honeysuckle in a microsite resulted in greater light competition from above for native understory plant species. Beyond increased cover and shading, our results do not provide evidence of duration-related effects from long-term dominance of honeysuckle in our sampled mixed hardwood forest sites.

Nomenclature: Amur honeysuckle; Lonicera maackii (Rupr.) Herder.

Management Implications: Nonnative invasive plants continue to pose one of the most serious threats to ecosystems worldwide. While the negative effects of invasive plants have been well documented, it is still unclear how the combined effect of duration of invasion and intensity (amount of occupied growing space) of an invader can influence native diversity at the microsite scale. We addressed this knowledge gap by examining how the duration and intensity of Amur honeysuckle invasion influenced the diversity and abundance of native plants in hardwood ecosystems of Indiana. Our results indicated that while percent cover of Amur honeysuckle in the upper vertical stratum (1.01 to 5 m) exhibited a strong negative correlation with native plant diversity and abundance at the microsite scale, duration of Amur honeysuckle invasion was not important when honeysuckle percent cover was included in the statistical models. However, when only duration of invasion was considered, it did show a significant negative correlation with native plant diversity and abundance and upper-stratum honeysuckle cover. It therefore appears that microsites where Amur honeysuckle has persisted longer contain a greater percent cover of this invasive shrub, resulting in greater light competition from above and reduced diversity and abundance of native flora. Information about the combined effects of Amur honeysuckle invasion intensity and duration can help forest managers prioritize control efforts in areas where existing sources of native plant propagules are present in microsites where Amur honeysuckle invasion is less intense. Also, our results suggest that the rate of community recovery after honeysuckle removal may not be heavily influenced by cumulative effects related to the duration of invasion. Such information is important for management efforts to support the long-term recovery of native plant communities in invaded ecosystems. Such information may be critical to the long-term recovery of native plant communities in these invaded ecosystems.

Ventenata dubia is an exotic winter annual grass that has invaded Conservation Reserve Program (CRP) lands, improved pastures, intensively managed hay fields, and rangelands within the Intermountain Pacific Northwest (PNW). Currently, producers are attempting to develop V. dubia management strategies with little knowledge of its life history traits. We conducted several studies to characterize V. dubia life history patterns. Preliminary germination trials were completed to describe primary and secondary dormancy characteristics. Field studies were conducted to evaluate (1) seed bank persistence patterns, (2) seedling emergence patterns under V. dubia litter, and (3) seedling emergence and phenological development patterns within timothy hay, CRP, and rangeland habitats. Preliminary germination trials suggest that the after-ripening period required for loss of dormancy does not exceed 30 d and that dormancy breakdown peaks at approximately 90 d, after which germination occurs over a wide range of temperatures (9 to 29 C). A small fraction (< 1%) of the seed bank remained germinable up to 3 yr after burial at 2 cm depth in a grassland habitat. Seedling emergence and survival was significantly greater under high V. dubia litter layers (100% cover) compared with bare surface during the drier study year because of higher soil moisture levels maintained under litter. Across habitat types, mean seedling emergence (50% of total) occurred between 33 and 94 growing degree days (GDD) after soil moisture rose above the permanent wilting point in the fall. Seedling emergence periodicity varied among habitat types in relation to spring seedling emergence, ranging from 0 to 13% of total emergence per year. Phenological development differed across sites and years by up to several hundred GDDs but was closely aligned to Julian days. This collection of studies improves our understanding of V. dubia life history traits and will aid integrated weed management strategies in the Intermountain PNW.

Nomenclature: North Africa grass; Ventenata dubia (Leers) Coss.; timothy; Phleum pratense L.

Management Implications: Ventenata dubia is an exotic annual grass that has invaded established CRP lands, improved pastures, intensively managed hay fields, and rangelands within the Intermountain PNW. Significant economic and ecological impacts have resulted from V. dubia invasions across perennial grass habitats in recent years, underscoring the need for development of integrated control strategies. Control of V. dubia using selective herbicides within perennial grass stands, as well as cultural control strategies, will benefit from greater understanding of V. dubia life history patterns.

Within the Intermountain PNW, V. dubia seedling emergence occurs after fall rains have increased soil moisture above the PWP in timothy hay, CRP, and rangeland habitats. The greatest proportion of fall seedling emergence occurs within 6 wk of initial emergence. Spring seedling emergence is more likely in timothy hay and rangeland habitats where fall environmental conditions are less conducive for seedling emergence and survival in the Intermountain PNW. At a local scale, seedling emergence and survival is likely mediated by the amount of residue at the soil surface. Higher V. dubia litter levels will increase seedling emergence and survival compared with bare surface during drier or colder fall growing seasons. A small fraction of V. dubia seed banks (< 1%) may remain persistent, or germinable, for up to 3 yr at shallow soil depths (2 cm).

These life history traits should inform V. dubia management strategies in the Intermountain PNW. Ventenata dubia may be controlled with early postemergence herbicide applications in late fall. However,

Downy brome inhibits revegetation efforts following ecosystem disturbance. Imazapic is a commonly used herbicide for downy brome management, but more information is needed regarding effective application timing for restoration efforts. We wished to determine (1) if native species establishment exhibited a tradeoff between downy brome competition and injury from herbicide and (2) if this differed between pre- and postemergent applications of imazapic. We used a standard replacement series design and overlaid herbicide treatments. Nine weeks after planting, aboveground biomass was harvested and relative yield (RY) indices calculated. Both imazapic applications reduced downy brome biomass by 91% or more (P < 0.05). Imazapic caused drastic reductions in native biomass but less than what was caused by downy brome competition (P < 0.05). Natives were less injured by a pre- than postemergent application (P < 0.05). In situations where downy brome may impact restoration efforts, pre-emergent applications of imazapic at 70 g ai ha⁻¹ (0.06 lb ai ac⁻¹) may reduce downy brome with less negative impacts on newly-seeded native grasses than post-emergent applications. Ensuring sufficient proportions of native species seeds on restoration sites may reduce downy brome.

Nomenclature: Imazapic; blue grama; Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths; downy brome; Bromus tectorum L.; needle-and-thread; Hesperostipa comata (Trin. & Rupr.) Barkworth; western wheatgrass; Pascopyrum smithii (Rydb.) Á. Löve).

Management Implications: Downy brome, a highly competitive invasive grass in the western US, inhibits revegetation efforts following disturbance. While mature perennial grasses may be good competitors against downy brome, seedlings are not. Downy brome control and reseeding efforts may be equally important to revegetation success. Imazapic is a commonly used herbicide for downy brome management, but more information is needed regarding effective application timing for restoration efforts.

We reduced downy brome biomass by 91% or more with a relatively low imazapic rate applied either pre- or post-emergent. Since both application timings provided similar downy brome reduction, managers should focus on the application timing that maximizes native perennial grass production. While imazapic reduced perennial grass growth, downy brome competition caused greater reductions. A pre-emergent application led to less perennial grass biomass reduction overall. Thus, if seeding natives in the fall, it may be beneficial to preemptively apply imazapic instead of reacting after downy brome seedling emergence. Ensuring sufficient proportions of native seeds at a site may also help reduce downy brome. Native seedlings exerted competitive interference upon downy brome and reduced downy brome biomass more than expected from reductions in downy brome seeding.

Our study continues to highlight the need to control downy brome infestations at early stages prior to the loss of mature native perennial grasses – not only to facilitate brome control, but to facilitate perennial grass dominance. Established perennial grasses are better able to withstand the stressors imposed by herbicide and downy brome competition. When the reseeding of native perennials is necessary, it may be desirable to use high seeding rates to increase the proportion of natives in the seedbank or methods to reduce downy brome seedbanks and competition.

Invasion by nonnative plants may have ecosystem-wide effects, altering the decomposition rate of plant material via changes in litter quality or altered environment (abiotic conditions, associated biotic community), or both. Yet, the relative importance of these factors for decomposition rates is not clear. We studied decomposition using the leaves of related shrub species (nonnative Sorbaria sorbifolia and Rosa rugosa, native Rubus idaeus) with comparable physiognomy but different leaf characteristics and origin (alien vs. native) in patches formed by S. sorbifolia and Rubus idaeus in southwestern Finland. Decomposition of cellulose in the topsoils of the patches was also studied. Using litter bags, we found that S. sorbifolia leaf litter decomposed slowest and Rosa rugosa leaves fastest irrespective of patch type. Topsoils in S. sorbifolia patches were richer in carbon, nitrogen, and calcium than those of Rubus idaeus, but these differences did not affect decomposition rates. Very little decomposition appeared to happen during the winter but during the summer, microclimate had minor but significant effects on decomposition rates. Our results highlight the key role of litter source in the decomposition of plant material. Between-patch differences in abiotic conditions appear to play a minor role relative to litter quality.

Nomenclature: False spirea; Sorbaria sorbifolia (L.) A. Braun; rugosa rose; Rosa rugosa Thunb.; red raspberry; Rubus idaeus L.

Management Implications: Decomposition of plant material is crucial for nutrient cycling. Invasive woody species may alter decomposition rates by altering litter quality and by altering the environmental conditions below the plants. We compared the leaf decomposition of a native and two nonnative shrubs in environments created by the native and one of the nonnative shrubs to estimate the relative importance of leaf source (species identity) and environment (microclimatic conditions, soil nutrient levels) for leaf decomposition rates. All shrubs belonged to the same family (Rosaceae) and had comparable physiognomy and leaf biomass production, which helped to minimize the influence of confounding factors. Our results demonstrate how the decomposition rate of leaves depends on species-specific differences in the quality of leaves rather than on the minor differences in the environments created by the patch-forming shrubs. The predominant importance of leaf source has been stressed also in some previous studies, suggesting that our conclusions can be generalized to a wider group of woody species. Although our conclusions can be regarded as preliminary rather than conclusive due to the small number of studied species, our results suggest that evaluations based solely on changes in leaf litter quality (and quantity) may capture the essential changes in leaf decomposition rates after an invasion of a nonindigenous plant. However, our results also indicate that species-specific differences in leaf quality prevent generalizations across all species, so the consequences of plant invasions for decomposition rates should be evaluated at the level of plant species.

To assess the potential invasiveness of common eucalyptus species planted for pulpwood, mulch wood or bioenergy crops, field surveys of eucalyptus seedling recruitment were conducted in north and central Florida locations within seed bearing eucalyptus stands and in the proximate plant communities where seed dispersal may occur. Plant communities included non-grazed pasture, intensively site-prepared forestland, abandoned forest road and upland mixed pine- hardwood forest. No eucalyptus seedlings were found in any of the 310 1-m² survey plots across the two locations. Second, seed addition studies were conducted to determine the relative potential for seedling emergence and survival among Eucalyptus amplifolia, E. camaldulensis and E. grandis added into plots at two seed densities, under disturbed and nondisturbed conditions, in the understory of the eucalyptus stands and in each of the aforementioned proximate plant communities. Overall, the probability of emergence of added seed was very low (P  =  0.0 to 0.0032), and seed density effects were not significant. Emergence was significantly greater in disturbed conditions compared to nondisturbed conditions for seedlings originating from natural seed rain from the eucalyptus canopy in central Florida. The amount of time that seedlings survived was greater for E. camaldulensis compared to the other species but no seedlings survived more than 13 wk. These data indicate that under specific favorable conditions, eucalyptus seedlings may establish within or proximate to planted stands, but the overall level of invasiveness demonstrated by E. amplifolia and E. grandis is low for north or central Florida. The demonstrated role of disturbance in facilitating eucalyptus seedling recruitment suggests that a stable perennial plant community (native grasses) should be established instead of bare soil buffer zones to mitigate spread.

Nomenclature: Cabbage gum (Eucalyptus amplifolia Naudin); yellow mallee (Eucalyptus incrassata Labill.); river red gum (Eucalyptus camaldulensis Dehnh.); rose gum [Eucalyptus grandis W. Hill ex Maiden].

Management Implications: Because of its potential for fast growth and high fiber yields, eucalyptus plantations are being established in the southeastern US Coastal Plain as a source of pulpwood, mulch wood and possibly biofuel. Two quantitative study approaches used within seed bearing Eucalyptus amplifolia stands and their proximate native and modified plant communities in north and central Florida found low invasive potential overall. Surveys at the two locations found no eucalyptus recruitment, suggesting limited success for seedling establishment. The subsequent study evaluated the invasive potential of three commercially important eucalyptus species by adding seed at two densities to disturbed (forest litter or vegetation removed to expose mineral soil) and nondisturbed sites. The combined research findings demonstrated that eucalyptus seedling establishment and survival were generally low at the northern and central Florida locations, although greater numbers of seedlings were observed in disturbed conditions, within the eucalyptus stands and for E. camaldulensis as compared to E. grandis or E. amplifolia. Seed addition at 500 or 1000 expected germinants per m² did result in seedling establishment, but no seedlings survived more than 13 wk. Whereas these results do not support previous weed risk assessment conclusions of high invasion risk for E. camaldulensis, they suggest that caution is warranted regarding the cultivation of E. camaldulensis, especially concerning practices that might increase soil disturbance near eucalyptus stands. The demonstrated role of disturbance in facilitating eucalyptus seedling recruitment suggests that perennial

Aminopyralid is the most commonly used herbicide for the control of yellow starthistle and other invasive thistles in annual grasslands of California. Although the effects of aminopyralid on native plant communities over a 2-yr period have been evaluated in prairies dominated by perennial species in the northern central states, similar evaluations have not been conducted in grassland communities of California, which are generally composed of a high diversity of native and nonnative annual species. In this study we monitored the effects of 53 and 123 g ae aminopyralid ha⁻¹ on individual species cover and species richness over three growing seasons in two locations on California annual grassland. Treated plots were compared to untreated plots in randomized complete-block designs. Results were largely consistent between the two trials. In the first season after treatment, both rates of aminopyralid reduced dicot cover significantly, particularly members of the Asteraceae and Fabaceae. Treated plots also showed reduced species richness. However, these differences were less pronounced in the second season after treatment, particularly at the low rate. By the third season after treatment in both sites, there were no longer any significant effects on cover or species richness at the low herbicide rate. On California annual grasslands, winter applications of low rates of aminopyralid have been shown to give excellent control of yellow starthistle, providing long-term benefits to grassland ecosystems. Results of the current study suggest that negative impacts of aminopyralid on the desirable native forb community are transitory.

Nomenclature: Aminopyralid; yellow starthistle; Centaurea solstitialis L.

Management Implications: Although land managers should, and generally do, consider the impact of invasive plant control methods on the desired vegetation and the ability to achieve their management goals, they often do not have the necessary information on the long-term effects of these control options. The primary control method for yellow starthistle and other invasive species, particularly thistles, is the herbicide aminopyralid. It is well recognized that members of the Asteraceae, Fabaceae, Apiaceae, and a few other families are particularly sensitive to aminopyralid. In this repeated study, we monitored the effect of high and low registered rates of aminopyralid on species cover and richness on California grasslands dominated by annual grasses and forbs. Our results demonstrated a significant impact on forb cover in the first season after treatment with both herbicide rates, but the response was transitory and by the third season after treatment there were no longer any negative impacts on the native plant community, including nearly all sensitive species. Although we do not know the long-term effect of aminopyralid when it is applied in multiple years, we previously showed that following a summer prescribed burn with a winter aminopyralid application provided nearly complete control of yellow starthistle without requiring multiple years of aminopyralid treatment. Under this integrated approach, it may be possible to achieve the desired control of invasive thistles with only a transitory effect on nontarget native plants.