Pollination Ecology and Seed Production of Rhododendron Ponticum in Native and Exotic Habitats

Alien plants may be reproductively limited in exotic habitats because of a lack of mutualistic pollinators. However, if plants are adequately served by generalist pollinators, successful reproduction, naturalisation and expansion into exotic habitats may occur. Rhododendron ponticum is very successful, ecologically damaging invasive plant in Britain and Ireland, but is in decline in its native Iberian habitat. It spreads locally by sending out lateral branches, but for longer distance dispersal it relies on sexually produced seeds. Little is known about R. ponticum's pollination ecology and breeding biology in invaded habitats. We examined the flower-visiting communities and maternal reproductive success of R. ponticum in native populations in southern Spain and in exotic ones in Ireland. R. ponticum in flowers are visited by various generalist (polylectic) pollinator species in both native and exotic habitats. Although different species visited flowers in Ireland and Spain, the flower visitation rate was not significantly different. Insects foraging on R. ponticum in Spain carried less R. ponticum pollen than their Irish counterparts, and carried fewer pollen types. Fruit production per inflorescence varied greatly within all populations but was significantly correlated with visitation at the population level. Nectar was significantly depleted by insects in some exotic populations, suggesting that this invasive species is providing a floral resource for native insects in some parts of Ireland. The generality of the pollination system may be factor contributing to R.ponticum's success in exotic habitats.     

Reducing Competitive Suppression of a Rare Annual Forb by Restoring Native California Perennial Grasslands

Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m² experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m²), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m²) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.     

Response of a Native Perennial Grass Stand to Disturbance in California's Coast Range Grassland

To assess the potential for enhancing an existing stand of native perennial grasses on a California Coast Range Grassland site, we experimentally manipulated the seasonal timing and presence of grazing for 3 years (1994 through 1996) and of autumn burning for 2 years (1994 and 1995) and measured species cover for 6 years (1993 through 1998). We subjected the species matrix to classification (TWINSPAN) and ordination (CCA) and tested the ordination site scores as well as diversity indices with linear mixed effects models. Four distinct plant community groups emerged from the classification. Two of these were dominated by annual grasses and two by perennial grasses. No treatment effects were observed on diversity. For composition, temporal and spatial random effects were important mixed effects model parameters, as was the fixed effect covariate, pre‐treatment CCA site score, indicating the importance of random environmental variation and initial starting conditions. Incorporation of these random effects and initial condition terms made for more powerful tests of the fixed effects, grazing season, and burning. We found no significant burning effects. Grazing removal imparted a shift in plant community from more annual‐dominated toward more perennial‐dominated vegetation. Individual perennial grass species responded differently according to genus and species. Nassella spp. increased gradually over time regardless of grazing treatment. Nassella pulchra (purple needlegrass) increase was greatest under spring grazing and N. lepida (foothill needlegrass) was greatest with grazing removal. Danthonia californica (California oatgrass) had little response over time under seasonal grazing treatments, but increased with grazing removal. Under relatively mesic weather conditions it appears that grazing removal from Coast Range Grasslands with existing native perennial grass populations can increase their cover. However if N. pulchra is the sole existing population, spring season‐restricted grazing should be equally effective at enhancing cover of the native grass species.     

Emergence of the Introduced Grass Agropyron cristatum and the Native Grass Bouteloua gracilis in a Mixed-grass Prairie Restoration

Abstract Prairie restoration at the northern edge of the Great Plains can be frustrated by previously established non‐native perennial grasses. We compared the emergence of a widely introduced grass, Agropyron cristatum, and a common native grass, Bouteloua gracilis, in a 4‐year‐old field experiment in which the Agropyron‐dominated vegetation had either been left intact or treated annually with herbicide. This was done at two levels of water supply, reflecting conditions expected in wet and dry years, to examine the effects of among‐year variability in precipitation. Water addition significantly increased the emergence of both surface‐sown and buried (1 cm deep) seeds. Herbicide treatment of neighbors did not increase the emergence of experimentally added seeds. Emergence was much greater for buried (80%) than surface‐sown seeds (20%). Significantly more Bouteloua than Agropyron germinated from experimentally buried seeds. Whereas only a single seedling of Bouteloua emerged from the existing seed bank, the mean density of Agropyron seedlings emerging from the seed bank was 930/m² (range, 0 to 6,455/m²). Surprisingly, the emergence of Agropyron from the seed bank was not decreased by 4 years of herbicide treatment, possibly because herbicide may release Agropyron from intraspecific competition and allow increased seed production to compensate for decreased plant abundance. In summary, we found few differences between Agropyron and Bouteloua in spring and summer emergence at high or low water availability. The persistence of Agropyron stands despite repeated herbicide application may be partly due to increased seed production.     

Restoration of California Native Grasses and Clovers: The Roles of Clipping,Broadleaf Herbicide,and Native Grass Density

One of the major challenges confronting grassland restoration of highly invaded communities is increasing the diversity of native species. There is surprisingly little research investigating how reconstructed native grasslands respond to common management techniques and how these techniques influence the relative establishment of both native grasses and forbs. Despite the diversity and wide distribution of native clovers in California, few practitioners incorporate them into grassland restoration plans. Conversely, non‐native clovers have been seeded extensively onto California rangelands. This study addresses the following questions: (1) Using readily available management tools, is there a strategy that can benefit the growth of both planted native bunchgrasses and seeded clovers? (2) Do native bunchgrasses compete with establishing clovers and non‐native grasses? (3) Do native and non‐native clovers differ in their response to management treatments or in their productivity? Plots were established to test three factors in different combinations over 3 years: (1) early spring clipping, (2) initial broadleaf herbicide, and (3) native bunchgrass planting density. Native and non‐native clovers were seeded in years 2 and 3. Early spring clipping did not have a significant effect on native bunchgrass cover, yet it did result in greater growth of native and non‐native clovers. The direction of the response to broadleaf herbicide changed between years for native bunchgrasses and was consistently negative for native clovers. Plots with higher native grass densities did not adversely affect the seeded clovers, yet non‐native grass cover was reduced. Native and non‐native clovers exhibited similar responses to clipping and established at similar densities.     

Exotic Grass Invasions: Applying a Conceptual Framework to the Dynamics of Degradation and Restoration in Australia’s Tropical Savannas

Plant invasions can cause severe degradation of natural areas. The ability of an ecosystem to recover autogenically from degradation following weed control is in part determined by the type and magnitude of changes to both biotic and abiotic processes caused by the invasion and how these interact with structural and functional components of the ecosystem. Recently, a number of conceptual frameworks have been proposed to describe the dynamics of degradation and regeneration in degraded ecosystems. We assessed the utility of one of these frameworks in describing the degradation and restoration potential of Australia’s tropical savannas following exotic grass invasion. First, we identified easily measured structural characteristics of putative states. We found that a continuous cover of the exotic grasses Gamba grass (Andropogon gayanus Kunth.) and Perennial mission grass (Pennisetum polystachion (L.) Schult.) under an intact tree canopy was a common state with an understorey characterized by reduced species richness and abundance and a change in the relative contribution of functional groups. Further degradation led to a state where the canopy was severely reduced and the impacts on the understorey were more severe. In both states, the seed bank was substantially less degraded than the understorey vegetation. Guided by the framework, we combined our study with other studies to construct a conceptual model for degradation in exotic grass‐invaded savannas.     

The Mark of Zorro: Effects of the Exotic Annual Grass Vulpia myuros on California Native Perennial Grasses

Native perennial grasses were once common in California prairies that are now dominated by annual grasses introduced from Europe. Competition from exotics may be a principal impediment to reestablishment of native perennial grasses. Introduced annual grasses, such as Vulpia myuros (zorro fescue), are often included with native perennial species in revegetation seed mixtures used in California. To examine the potential suppressive effect of this graminoid, we evaluated the growth and performance of a mixture of California native perennial grasses and resident weeds when grown with varying densities of V. myuros. The annual fescue exhibited a strongly plastic growth response to plant density, producing similar amounts of above‐ground biomass at all seeding densities. Perennial grass seedling survival and above‐ ground biomass decreased and individuals became thinner (i.e., reduced weight‐to‐height ratio) with increasing V. myuros seeding density. V. myuros also significantly suppressed above‐ground biomass and densities of weeds and had a more negative effect on weed densities than on native perennial grass densities. Biomass of native grasses and weeds was not differentially affected by increasing densities of V. myuros. Overall, because V. myuros significantly reduced the survival and performance of the mixture of native perennial grasses and this effect increased with increasing V. myuros density, we conclude that including this exotic annual in native seed mixtures is counterproductive to restoration efforts.     

Identifying Native Vegetation for Reducing Exotic Species during the Restoration of Desert Ecosystems

There is currently much interest in restoration ecology in identifying native vegetation that can decrease the invasibility by exotic species of environments undergoing restoration. However, uncertainty remains about restoration's ability to limit exotic species, particularly in deserts where facilitative interactions between plants are prevalent. Using candidate native species for restoration in the Mojave Desert of the southwestern U.S.A., we experimentally assembled a range of plant communities from early successional forbs to late‐successional shrubs and assessed which vegetation types reduced the establishment of the priority invasive annuals Bromus rubens (red brome) and Schismus spp. (Mediterranean grass) in control and N‐enriched soils. Compared to early successional grass and shrub and late‐successional shrub communities, an early forb community best resisted invasion, reducing exotic species biomass by 88% (N added) and 97% (no N added) relative to controls (no native plants). In native species monocultures, Sphaeralcea ambigua (desert globemallow), an early successional forb, was the least invasible, reducing exotic biomass by 91%. However, the least‐invaded vegetation types did not reduce soil N or P relative to other vegetation types nor was native plant cover linked to invasibility, suggesting that other traits influenced native‐exotic species interactions. This study provides experimental field evidence that native vegetation types exist that may reduce exotic grass establishment in the Mojave Desert, and that these candidates for restoration are not necessarily late‐successional communities. More generally, results indicate the importance of careful native species selection when exotic species invasions must be constrained for restoration to be successful.     

Effects of Flow Restoration and Exotic Species Removal on Recovery of Native Fish: Lessons from a Dam Decommissioning

Flow diversion and invasive species are two major threats to freshwater ecosystems, threats that restoration efforts attempt to redress. Yet, few restoration projects monitor whether removal of these threats improve target characteristics of the ecosystem. Fewer still have an appropriate experimental design from which causal inferences can be drawn as to the relative merits of removing exotic fish, restoring flow, or both. We used a dam decommissioning in Fossil Creek, Arizona, to compare responses of native fish to exotic fish removal and flow restoration, using a before‐after‐control‐impact design with three impact treatments: flow restoration alone where exotics had not been present, flow restoration and exotic fish removal, and flow restoration where exotics remain and a control reach that was unaffected by restoration actions. We show that removal of exotic fish dramatically increased native fish abundance. Flow restoration also increased native fish abundance, but the effect was smaller than that from removing exotics. Flow restoration had no effect where exotic fish remained, although it may have had other benefits to the ecosystem. The cost to restore flow ($12 million) was considerably higher than that to eradicate exotics ($1.1 million). The long‐term influence of flow restoration could increase, as travertine dams grow and re‐shape the creek increasing habitat for native fish. But in the 2‐year period considered here, the return on investment for extirpating exotics far exceeded that from flow restoration. Projects aimed to restore native fish by restoring flow should also consider the additional investment required to eradicate exotic fish.     

Exotic Slugs Pose a Previously Unrecognized Threat to the Herbaceous Layer in a Midwestern Woodland

Developing effective restoration strategies requires first identifying the underlying factors limiting native plant recovery. The slug Deroceras reticulatum is an important herbivore in Europe, a global agricultural pest, and is introduced and abundant throughout eastern North America, but little information is available on the effect of this exotic herbivore on the forest herbaceous layer. Here, we test the palatability of 12 forest herbs to the introduced slug D. reticulatum and use field surveys to determine the degree to which slugs are damaging plants in the field. In laboratory feeding trials, slugs readily consumed most plants, but avoided the grass Elymus virginicus, the invasive forb Alliaria petiolata (garlic mustard), and thicker leaved plants. In the field, we documented significant slug damage, with close to 50% or more of plant leaves damaged by slugs on five of the six native species tested. Slug damage in the field was predicted by laboratory‐determined acceptability, but was significantly greater on short‐statured rosette species than on erect plants for a given acceptability value. Our results identify introduced slugs as an important, but overlooked obstacle to forest herb restoration and potential drivers of larger scale understory compositional change. The relaxed herbivore pressure on A. petiolata, relative to native competitors, suggests that invasive plant removal alone may not result in the recovery of native flora. Rather, restoration of unpalatable native species should accompany invasive plant control in slug invaded areas. Erect forbs, thick‐leaved plants, and graminoids should have the greatest success where introduced slugs are abundant.     

Promoting Native Vegetation and Diversity in Exotic Annual Grass Infestations

Exotic plant invasions are especially problematic because reestablishment of native perennial vegetation is rarely successful. It may be more appropriate to treat exotic plant infestations that still have some remaining native vegetation. We evaluated this restoration strategy by measuring the effects of spring burning, fall burning, fall applied imazapic, spring burning with fall applied imazapic, and fall burning with fall applied imazapic on the exotic annual grass, medusahead (Taeniatherum caput‐medusae (L.) Nevski), and native vegetation at six sites in Oregon for 2 years post‐treatment. Medusahead infestations included in this study had some residual native perennial bunchgrasses and forbs. Burning followed by imazapic application provided the best control of medusahead and resulted in the greatest increases in native perennial vegetation. However, imazapic application decreased native annual forb cover the first year post‐treatment and density the first and second year post‐treatment. The spring burn followed by imazapic application produced an almost 2‐fold increase in plant species diversity compared to the control. The fall burn followed by imazapic application also increased diversity compared to the control. Results of this study indicate that native plants can be promoted in medusahead invasions; however, responses vary by plant functional group and treatment. Our results compared to previous research suggest that restoration of plant communities invaded by exotic annual grass may be more successful if efforts focus on areas with some residual native perennial vegetation. Thus, invasive plant infestations with some native vegetation remaining should receive priority for restoration efforts over near monocultures of invasive plant species.     

植物外来种的生态风险评估和管理

生物入侵是指物种借助于自身力量或外界力量 ,传入到其进化史上未曾分布过的地域 ,并能繁衍后代的过程。植物外来种的入侵可以通过多种途径 :如野生动物、风、水和人类的活动等传播 ,尤其是人类活动的影响使生物入侵的范围、频率和强度超过自然入侵。目前已有部分外来的植物被人们确定为生物污染剂。生物污染剂不同于化学污染剂 ,后者可以随时间而减弱或分解掉 ,而前者则有持久性、倍增性和传播性。有些入侵性的外来植物可以对自然资源造成不可挽救的破坏 ,使经过几千年协同进化的植物、动物、土壤和水分的生态平衡被破坏。当本地植物被外来…     

Competitive Control of an Exotic Mangrove Species: Restoration of Native Mangrove Forests by Altering Light Availability

Recently, many studies have focused on the possibility of restoring mangrove ecosystems by introducing fast‐growing mangroves. However, methods for managing an exotic fast‐growing species to restore mangrove ecosystems and at the same time preventing invasion by introduced species remains unclear. Sonneratia apetala Buch‐Ham is one example of an exotic mangrove with both high ecological value and potential risk for invasion after introduction. To investigate the possibility of reducing the potential for invasion by altering light availability, we simulated different irradiances of S. apetala understory in the greenhouse. For each irradiance treatment, three levels of competition between S. apetala and native mangroves Aegiceras corniculatum (L.) were used: no competition, intraspecific competition and interspecific competition. Compared with A. corniculatum, S. apetala showed a significantly higher growth rate for both height and biomass accumulation under full irradiation. Compared to the full irradiation treatment, the shading treatment significantly reduced the height, total biomass and biomass allocation to leaves of S. apetala by 61.31, 71.0, and 76.2%, respectively, whereas the growth of A. corniculatum was not affected. The results suggested that lowering light availability could inhibit the growth of S. apetala and increase the competitiveness of A. corniculatum. Planting introduced fast‐growing mangroves at a density of approximately 2,000 plants/hm² is an effective strategy for preventing potential invasion and restoring wetland habitats. By taking advantage of the differences in shade tolerance between fast‐growing exotic mangroves and native mangroves, introduction of fast‐growing mangroves in coastal areas could have huge potential for reforesting mangrove ecosystems.     

Native and Non‐Native Community Assembly through Edaphic Manipulation: Implications for Habitat Creation and Restoration

Chemical and physical (abiotic) conditions can be determining factors of community assembly and invasibility, but can this observation be used as a practical tool for habitat creation? Serpentine soils, in particular, have three abiotic components thought to confer invasion resistance: a low Ca:Mg ratio, low water‐retention capacity, and high concentrations of heavy metals. Consequently, not only do some serpentine‐adapted native plants persist only on serpentine soils, but also the community members that depend upon those plants become dependent upon serpentine as well. In an effort to provide additional habitat for the threatened and serpentine‐restricted Bay checkerspot butterfly (Euphydryas editha bayensis), we experimentally altered a non‐serpentine site to mimic the abiotic conditions of serpentine. Attempts to lower the Ca:Mg ratio of soils through the addition of MgSO₄ were unsuccessful. We then altered soil depth through the addition of gravel beds to determine the effects of water stress on native and non‐native community composition. We found that shallow soils had lower water content and correspondingly had significantly lower non‐native species richness and cover. The results present promising means, but also cautionary information, for habitat creation efforts and demonstrate the possible utility of edaphic manipulation in abating non‐native plant invasions. None of the experimental plots supported communities capable of sustaining E. editha populations, emphasizing that the manipulation of physical conditions is only likely to be successful in coordination with other restoration techniques.     

Herbicides Can Negatively Affect Seed Performance in Native Plants

Herbicides are widely used to control invasive non‐native plants in wildlands, yet there is little information on their non‐target effects, including on native plants that are intended to benefit from the treatment. Effects at the seed stage have been particularly understudied, despite the fact that managers commonly seed native plants immediately after herbicide application. We conducted a greenhouse experiment to explore the effects of two broadleaf‐specific herbicides (aminopyralid and picloram) on seedling emergence and biomass for 14 species that grow in dry grasslands of NW North America. For each species, we placed 50 seeds in soil‐filled pots that were sprayed with a water control or one of the herbicides at one of two rates (1× and 0.01× of the recommended rate). After 5 weeks, we assessed seedling emergence and dry aboveground biomass per pot. At the recommended rate (1×), both her bicides significantly suppressed seedling emergence and lowered biomass. At the diluted rate (0.01×), the effect of picloram was comparable to the effect at the recommended rate, whereas aminopyralid had no effect. There was no difference in effects of herbicides on native versus non‐native species. Although both herbicides are considered to be broadleaf‐specific, monocots were just as vulnerable as dicots at the recommended rate. Our results show that herbicides can harm non‐native and native plants at the seed stage, alike. Land managers should avoid spraying if recruitment of native species from the seedbank is a goal and should not seed directly after spraying .     

Balance of Competitive and Facilitative Effects of Exotic Trees on a Native Patagonian Grass

The balance between facilitation and competition in plants changes with species characteristics and environmental conditions. Facilitative effects are common in natural ecosystems, particularly in stressful environments or years. Contrarily, in artificial associations of plants, such as agroforestry systems, some authors have suggested that even when facilitative effects may occur, net balance of tree effects on grasses is usually negative, particularly in dry environments. The aim of this study was to determine the net effect of the exotic ponderosa pine on the native grass Festuca pallescens (St. Ives) Parodi in agroforestry systems in Patagonia. Soil water content, plant water status, and relative growth were measured in the grass growing in different treatments (determined by tree cover level) during two growing seasons with contrasting climatic conditions. Facilitative effects of trees over grass water status were recorded only when water availability was high. A net negative effect was detected on dates when soil water content was very low and evaporative demand was high. The strength of these negative effects depended on tree density and climatic conditions, being higher in treatments with lower tree canopy cover. These results indicate that the positive effect of trees could only be expected under relatively low stress conditions. However, relative growth of grasses was always similar in plants growing in forested plots than in open grassland. Differences in biomass allocation for grasses growing in shade and open habitats may reconcile these contrary results. Our results highlight the importance of the physiology of a species (relative drought and shade tolerance) in determining the response of a plant to a particular interacting species.     

Patterns of Growth and Soil-water Utilization in some Exotic Annuals and Native Perennial Bunchgrasses of California

In western California, exotic cool-season annuals appear tohave widely replaced native perennial bunchgrasses as the herbaceouscommunity dominants in grasslands, oak savannas, and oak woodlands.We argue that because these two herbaceous plant types possessvery different life histories, this invasion may have correspondinglyaltered seasonal patterns of soil-water availability. To beginto assess this hypothesis, in this study we compared exoticcool-season annuals and native perennial bunchgrasses in termsof growth, biomass allocation, rooting distribution, root morphology,and soil-water utilization. Exotic cool-season annuals completed their life cycle earlyin the dry season through rapid growth apparently made possibleby a high proportional allocation to shoots in combination withthe efficient production of roots of high specific root length.Further, annuals tended to concentrate root growth and soil-waterutilization in the upper soil profile. In contrast, native perennialbunchgrasses allocated a high proportion of their biomass tothe production of a deep root system, which allowed them tocontinue soil-water utilization well into the dry season andcontribute to the formation of a very dry soil profile. Takentogether, these contrasting patterns suggest that the invasionof exotic cool-season annuals might have produced a correspondingincrease in the amount of water present at depth in the soilprofile during the dry season. Brachypodium distachyon ; Bromus diandrus ; Cynosurus echinatus ; Elymus glaucus ;Nassella pulchra ; Trifolium hirtum ; soil-water utilization; specific root length; growth analysis; rooting depth     

Arbuscular Mycorrhizal Assemblages in Native Plant Roots Change in the Presence of Invasive Exotic Grasses

Plant invasions have the potential to significantly alter soil microbial communities, given their often considerable aboveground effects. We examined how plant invasions altered the arbuscular mycorrhizal fungi of native plant roots in a grassland site in California and one in Utah. In the California site, we used experimentally created plant communities composed of exotic (Avena barbata, Bromus hordeaceus) and native (Nassella pulchra, Lupinus bicolor) monocultures and mixtures. In the Utah semi-arid grassland, we took advantage of invasion by Bromus tectorum into long-term plots dominated by either of two native grasses, Hilaria jamesii or Stipa hymenoides. Arbuscular mycorrhizal fungi colonizing roots were characterized with PCR amplification of the ITS region, cloning, and sequencing. We saw a significant effect of the presence of exotic grasses on the diversity of mycorrhizal fungi colonizing native plant roots. In the three native grasses, richness of mycorrhizal fungi decreased; in the native forb at the California site, the number of fungal RFLP patterns increased in the presence of exotics. The exotic grasses also caused the composition of the mycorrhizal community in native roots to shift dramatically both in California, with turnover of Glomus spp., and Utah, with replacement of Glomus spp. by apparently non-mycorrhizal fungi. Invading plants may be able to influence the network of mycorrhizal fungi in soil that is available to natives through either earlier root activity or differential carbon provision compared to natives. Alteration of the soil microbial community by plant invasion can provide a mechanism for both successful invasion and the resulting effects of invaders on the ecosystem.     

Effects of Native and Non-Native Grassland Plant Communities on Breeding Passerine Birds: Implications for Restoration of Northwest Bunchgrass Prairie

One common problem encountered when restoring grasslands is the prominence of non-native plant species. It is unclear what effect non-native plants have on habitat quality of grassland passerines, which are among the most imperiled groups of birds. In 2004 and 2005, we compared patterns of avian reproduction and the mechanisms that might influence those patterns across a gradient of 13 grasslands in the Zumwalt Prairie in northeastern Oregon that vary in the degree of non-native plant cover (0.9–53.4%). We monitored the fate of 201 nests of all the breeding species in these pastures and found no association of percent non-native cover with nest densities, clutch size, productivity, nest survival, and nestling size. Regardless of the degree of non-native cover, birds primarily fed on Coleoptera, Orthoptera, and Araneae. But as percent non-native cover in the pastures increased, Orthoptera made up a greater proportion of diet and Coleoptera made up a smaller proportion. These diet switches were not the result of changes in terrestrial invertebrate abundance but may be related to decreases in percent bare ground associated with increasing cover of non-native vegetation. Measures of nest crypticity were not associated with cover of non-native vegetation, suggesting that predation risk may not increase with increased cover of non-native vegetation. Thus, the study results show that increased non-native cover is not associated with reduced food supplies or increased predation risk for nesting birds, supporting the growing body of evidence that grasslands with a mix of native and non-native vegetation can provide suitable habitat for native grassland breeding birds.     

Spacing and Competition Between Planted Grass Plugs and Preexisting Perennial Grasses in a Restoration Site in Oregon

Planting native species into restoration settings where other natives already occur is a common practice. However, the competitive consequences of such plantings are rarely studied. Planting density also affects restoration costs. Here we examined the effects of established individuals of Lemmon's needlegrass (Achnatherum lemmonii) on plugs of bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis) in a restoration site in Oregon. All three of these grasses are local native perennials. Plugs were planted at 6, 12, and 18 cm from established A. lemmonii bunchgrasses and also in plots without A. lemmonii neighbors. Plug survival was uniformly high, averaging more than 98%. Plugs planted at 6 cm from established grasses showed significantly lower growth and reproduction than plugs planted at 18 cm, which had similar values to plugs not planted in the vicinity of A. lemmonii. These results suggest that interplanting distances of as little as 18 cm were sufficient to greatly reduce competitive effects on newly planted plugs, at least in early establishment at this site.