Invasive species cover,soil type,and grazing interact to predict long‐term grassland restoration success

Grasslands are undergoing tremendous degradation as a result of climate change, land use, and invasion by non‐native plants. However, understanding of the factors responsible for driving reestablishment of grassland plant communities is largely derived from short‐term studies. In order to develop an understanding of the factors responsible for longer term restoration outcomes in California annual grasslands, we surveyed 12 fields in Davis, CA, U.S.A., in 2015 that were seeded with native species mixtures starting in 2004. Using field surveys, we investigated how invasive plant richness and cover, native plant richness and cover, aboveground biomass, grazing, soil type, and restoration species identity might provide utility for explaining patterns of restoration success. We found a negative relationship between invasive cover and restoration cover, which was attributed to the slow establishment of seeded species and subsequent dominance by weeds. The relationship between invasive cover and restoration cover was modified by grazing, likely due to a change in the dominance of exotic forbs, which have a more similar growing season to restoration species, and therefore compete more strongly for late season moisture. Finally, we found that soil type was responsible for differences in the identity and abundance of invasive plants, subsequently affecting restoration cover. This work highlights the value of focusing resources on reducing invasive species cover, limiting grazing to periods of adequate moisture, and considering soil type for successful long‐term restoration in California annual grasslands. Moreover, observations of long‐term restoration outcomes can provide insight into the way mechanisms driving restoration outcomes might differ through time.     

Adaptation of plant‐mycorrhizal interactions to moisture availability in prairie restoration

The strength and direction of plant response to inoculation with arbuscular mycorrhizal fungi (AM fungi) is dependent on both abiotic and biotic contexts, often generating patterns of AM fungal mediation of plant adaptation. However, knowledge of plant‐community level effects of these interactions in grassland restoration is limited. We conducted a field inoculation experiment by inoculating five plant species native to a drier prairie and five plant species native to a moister prairie with mycorrhizal fungal communities from each prairie type. Species were paired by genus or family to account for phylogenetic effects. The inoculated plants were transplanted to study plots seeded with a restoration seed mix. Plots were manipulated to create either moister or drier conditions similar to environments of the plant species and mycorrhizal communities. In both transplanted and seeded plant species, we found that only drier prairie‐range species benefited from moisture‐regime matched AM fungal inoculum. Other seeded prairie plant species demonstrated a negative response to inoculation, likely due to the earlier successional stage of these species. Additionally, nonseeded plants benefited from inoculation in different ways: native nonseeded plants had highest cover with drier prairie inoculum in drier conditions, while nonnative plants had highest cover with moister prairie‐origin inoculum. These results suggest that use of local AM fungi may be particularly important in restorations at drier sites, even at relatively small differences in moisture availability. Further, specific knowledge of relative responsiveness of seeded plant species and nonseeded plant species to AM fungal inoculation will be useful in planning restorations.     

The good with the bad: when ecological restoration facilitates native and non‐native species

Organisms interact with each other along a spectrum ranging from competition to facilitation. A theme in restoration ecology is tipping the balance of these interactions to favor desired species and site conditions, exemplified by restoring fertile islands and their nurse plant effects to encourage plant recruitment. We tested the effectiveness of outplanting nursery‐grown native perennials and vertical mulching (placing dead plant material upright in soil) for stimulating annual plant recruitment in a disturbed Mojave Desert shrubland in Joshua Tree National Park, California, U.S.A. Over 9 years, differences in annual species richness and cover between interspaces and below outplants and vertical mulch varied among years, potentially via inter‐annual fluctuations in precipitation or maturation of restoration sites. In the ninth year, which was the wettest, both native and non‐native cover averaged 3× higher below outplants than in interspaces. Overall among years at the microsite scale, non‐native annual plants more consistently exploited environments provided by outplants and vertical mulch structures than did native annuals. However, these restoration structures were important for native annual diversity. At the 40‐m² plot scale, disturbed plots that received outplanting supported greater richness of native annual species than disturbed unrestored plots. By facilitating both non‐native and native plants, reestablishing fertile islands to restore dryland ecosystems is a conundrum for restoration. Treatments reducing non‐native plants may need to accompany fertile island restoration to tip the balance of facilitative plant interactions in favor of native species.     

Initial soil amendments still affect plant community composition after nine years in succession on a heavy metal contaminated mountainside

Many efforts to restore disturbed landscapes seek to meet ecological goals over timescales from decades to centuries. It is thus crucial to know how different actions available to restoration practitioners may affect ecosystems in the long term, yet few such data exist. Here, we test the effects of seed and compost applications on plant community composition 9 years after their application, by taking advantage of a well‐controlled restoration experiment on a mountainside severely degraded by over 80 years of zinc smelting emissions. We asked whether plots have converged on similar plant communities regardless of initial seed and compost treatments, or if these initial treatments have given rise to lasting differences in whole plant communities or in the richness and abundance of native, exotic, and planted species. We found that compost types significantly affected plant communities 9 years later, but seed mix species composition did not. Observed differences in species richness and vegetative cover were negatively correlated, and both were related to the differences in plant communities associated with different compost types. These observed differences are due primarily to the number and abundance of species not in original seed mixes, of which notably many are native. Our results underscore the importance of soils in shaping the aboveground composition of ecosystems. Differences in soil characteristics can affect plant diversity and cover, which are both common restoration targets. Even in highly polluted and devegetated sites, compost and seed application can reinstate high vegetative cover and allow continued colonization of native species.     

Restoring a Mediterranean‐climate shrub community with perennial species reduces future invasion

Successful restoration of an invaded landscape to a diverse, invasion‐resistant native plant community requires determining the optimal native species mix to add to the landscape. We manipulated native seed mix (annuals, perennials, or a combination of the two), while controlling the growth of non‐native species to test the hypothesis that altering native species composition can influence native establishment and subsequent non‐native invasion. Initial survival of native annuals and perennials was higher when seeded in separate mixes than when combined, and competition between the native perennials and annuals led to lower perennial cover in year 2 of mixed‐seeded plots. The plots with the highest perennial cover had the highest resistance to invasion by Brassica nigra. To clarify interactions among different functional groups of natives and B. nigra, we measured competitive interactions in pots. We grew one native annual, one native perennial, and B. nigra alone or with different competitors and measured biomass after 12 weeks. Brassica nigra was the strongest competitor, limiting the growth of all native species, and was not impacted by competition with native annuals or perennial seedlings. Results from the potted plant experiment demonstrated the strong negative influence of B. nigra on native seedlings. Older native perennials were the strongest competitors against invasive species in the field, yet perennial seedling survival was limited by competition with native annuals and B. nigra. Management action that maximizes perennial growth in early years may lead to a relatively more successful restoration and the establishment of an invasion‐resistant community.     

Establishment of Restoration Trajectories for Upland Tundra Communities on Diamond Mine Wastes in the Canadian Arctic

Mining in the arctic amplifies restoration challenges due to inherent environmental conditions by removing soil, vegetation, and the propagule bank, adding coarse textured wastes with low water holding capacity and nutrients, and introducing salt and metal contamination. Short‐term reclamation focuses on rebuilding soil and providing rapid native plant cover for erosion control, supporting longer term reestablishment of ecological processes for sustainable tundra communities that provide essential wildlife habitat. This study evaluated methods to restore soil and plant communities 5 years after implementation of treatments at a diamond mine in the Canadian arctic. Five substrates including mine waste materials (processed kimberlite, glacial till, gravel, and mixes), four amendments (inorganic fertilizer, salvaged soil, sewage sludge, and water treatment sludge), five native species seed mixes and natural recovery were investigated. Soil and plant response were assessed annually. Soil chemistry was ameliorated with time. Chromium, cobalt, and nickel concentrations in processed kimberlite remained high and potentially toxic to plants. Adding fine textured materials such as glacial till to mine wastes improved nutrient and water retention, which in turn enhanced revegetation. Sewage and inorganic fertilizer increased available nitrogen and phosphorus, plant density and cover. Soil amendment increased species richness. Seeding was essential to establish a vegetation cover. After 5 years, seed mix composition and diversity had no effect on plant community development; soil and plant community properties among treatments changed considerably, providing evidence that restoration in the arctic is dynamic yet slow and success cannot be determined in the short term.     

Are two strategies better than one? Manipulation of seed density and soil community in an experimental prairie restoration

Restoration practitioners have a variety of practices to choose from when designing a restoration, and different strategies may address different goals. Knowledge of how to best use multiple strategies could improve restoration outcomes. Here, we examine two commonly suggested strategies in a single tallgrass prairie restoration experiment: increased forb sowing density and prairie soil inoculation. We designed a study with two different forb seeding densities. Within these densities, we transplanted seedlings into 1‐m² plots that had been grown in either a whole prairie soil inoculum or sterilized prairie soil. After 4 years, we found positive effects of both high forb sowing density and inoculation treatments on the ratio of seeded to nonseeded plant cover in these plots, and negative effects of both treatments on nonseeded plant diversity. No effects of either treatment were seen on seeded plant diversity. Each strategy also affected the plant community in different ways: high forb sowing density increased seeded forb richness and decreased native nonseeded plant cover, while inoculation decreased non‐native cover, and tended to increase average successional stage of the community. These effects on restoration outcome were typically independent of each other, with the result that plots with both manipulations had the most positive effects on restoration outcomes. We thus advocate the combined use of these restoration strategies, and further studies which focus on both seeding and soil community manipulation in restoration.     

Post‐fire vegetation dynamics in nutrient‐enriched and non‐enriched sclerophyll woodland

Abstract Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low‐nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run‐off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: ‘Are there differences in post‐fire resprouting and germination of native and exotic species in nutrient‐enriched communities, compared with communities not disturbed by nutrient enrichment?’ We found that in non‐enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient‐enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient‐enriched. In nutrient‐enriched areas after fire, the diversity of native species was lower than in the non‐enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non‐enriched areas. We suggest that although fire can be a useful tool for short‐term removal of exotic plant biomass from nutrient‐enriched areas, it does not promote establishment of native species that were not already present.     

Revegetation Methods for High-Elevation Roadsides at Bryce Canyon National Park, Utah

Establishment of native plant populations on disturbed roadsides was investigated at Bryce Canyon National Park (BCNP) in relation to several revegetation and seedbed preparation techniques. In 1994, the BCNP Rim Road (2,683–2,770 m elevation) was reconstructed resulting in a 23.8‐ha roadside disturbance. Revegetation comparisons included the influence of fertilizer on plant establishment and development, the success of indigenous versus commercial seed, seedling response to microsites, methods of erosion control, and shrub transplant growth and survival. Plant density, cover, and biomass were measured 1, 2, and 4 years after revegetation implementation (1995–1998). Seeded native grass cover and density were the highest on plots fertilized with nitrogen and phosphorus, but by the fourth growing season, differences between fertilized and unfertilized plots were minimal. Fertilizers may facilitate more rapid establishment of seeded grasses following disturbance, increasing soil cover and soil stability on steep and unstable slopes. However the benefit of increased soil nutrients favored few of the desired species resulting in lower species richness over time compared to unfertilized sites. Elymus trachycaulus (slender wheatgrass) plants raised from indigenous seed had higher density and cover than those from a commercial seed source 2 and 4 years after sowing. Indigenous materials may exhibit slow establishment immediately following seeding, but they will likely persist during extreme climatic conditions such as cold temperatures and relatively short growing seasons. Seeded grasses established better near stones and logs than on adjacent open microsites, suggesting that a roughened seedbed created before seeding can significantly enhance plant establishment. After two growing seasons, total grass cover between various erosion‐control treatments was similar indicating that a variety of erosion reduction techniques can be utilized to reduce erosion. Finally shrub transplants showed minimal differential response to fertilizers, water‐absorbing gels, and soil type. Simply planting and watering transplants was sufficient for the greatest plant survival and growth.     

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.     

Community‐level plant–soil feedbacks explain landscape distribution of native and non‐native plants

Plant–soil feedbacks (PSFs) have gained attention for their potential role in explaining plant growth and invasion. While promising, most PSF research has measured plant monoculture growth on different soils in short‐term, greenhouse experiments. Here, five soil types were conditioned by growing one native species, three non‐native species, or a mixed plant community in different plots in a common‐garden experiment. After 4 years, plants were removed and one native and one non‐native plant community were planted into replicate plots of each soil type. After three additional years, the percentage cover of each of the three target species in each community was measured. These data were used to parameterize a plant community growth model. Model predictions were compared to native and non‐native abundance on the landscape. Native community cover was lowest on soil conditioned by the dominant non‐native, Centaurea diffusa, and non‐native community cover was lowest on soil cultivated by the dominant native, Pseudoroegneria spicata. Consistent with plant growth on the landscape, the plant growth model predicted that the positive PSFs observed in the common‐garden experiment would result in two distinct communities on the landscape: a native plant community on native soils and a non‐native plant community on non‐native soils. In contrast, when PSF effects were removed, the model predicted that non‐native plants would dominate all soils, which was not consistent with plant growth on the landscape. Results provide an example where PSF effects were large enough to change the rank‐order abundance of native and non‐native plant communities and to explain plant distributions on the landscape. The positive PSFs that contributed to this effect reflected the ability of the two dominant plant species to suppress each other's growth. Results suggest that plant dominance, at least in this system, reflects the ability of a species to suppress the growth of dominant competitors through soil‐mediated effects.     

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.     

Ecological outcomes of agroforests and restoration 15 years after planting

Large‐scale forest restoration relies on approaches that are cost‐effective and economically attractive to farmers, and in this context agroforestry systems may be a valuable option. Here, we compared ecological outcomes among (1) 12–15‐year‐old coffee agroforests established with several native shade trees, (2) 12–15‐year‐old high‐diversity restoration plantations, and (3) reference old‐growth forests, within a landscape restoration project in the Pontal do Paranapanema region, in the Atlantic Forest of southeastern Brazil. We compared the aboveground biomass, canopy cover, and abundance, richness, and composition of trees, and the regenerating saplings in the three forest types. In addition, we investigated the landscape drivers of natural regeneration in the restoration plantations and coffee agroforests. Reference forests had a higher abundance of trees and regenerating saplings, but had similar levels of species richness compared to coffee agroforests. High‐diversity agroforests and restoration plantations did not differ in tree abundance. However, compared to restoration plantations, agroforests showed higher abundance and species richness of regenerating saplings, a higher proportion of animal‐dispersed species, and higher canopy cover. The abundance of regenerating saplings declined with increasing density of coffee plants, thus indicating a potential trade‐off between productivity and ecological benefits. High‐diversity coffee agroforests provide a cost‐effective and ecologically viable alternative to high‐diversity native tree plantations for large‐scale forest restoration within agricultural landscapes managed by local communities, and should be included as part of the portfolio of reforestation options used to promote the global agenda on forest and landscape restoration.     

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.     

Plant community response following the removal of the invasive Lupinus arboreus in a coastal dune system

The removal of invasive species is common in restoration projects, yet the long‐term effects of pest management programs are seldom assessed. We present results of a long‐term program to remove the invasive species Lupinus arboreus (lupin) from sand dunes in New Zealand. We evaluate the response of plant communities to lupin removal, by comparing total plant cover, the cover of non‐native and native plant species, and species richness between sand dune sites where lupin removal has occurred, not occurred, and where lupin has never been present. Neither lupin presence nor removal had a significant impact on the foredune environment. Following removal, total and other non‐native plant cover remained higher, and the cover of several native sand dune species remained lower compared with uninvaded sites in the deflation and backdune environments. These changes can be attributed to persistent effects associated with the invasion of lupin, but have also developed in response to lupin removal. The results of this study have implications for restoration projects in sand dunes. Pest management alone is unlikely to be sufficient to restore plant communities. Given the difficulties in restoring plant communities once an invasive species has established, managers should prioritize actions to prevent the spread of invasive species into uninvaded areas of sand dunes. Finally, the response to lupin invasion and removal differed between dune habitats. This highlights the importance of tailoring a pest management program to restoration goals by, for example, prioritizing areas in which the impacts of the invading species are greatest.     

Response of Native and Exotic Grasses to Increased Soil Nitrogen and Recovery in a Postfire Environment

Native plant recovery following wildfires is of great concern to managers because of the potential for increased water run‐off and soil erosion associated with severely burned areas. Although postfire seeding with exotic grasses or cultivars of native grasses (seeded grasses) may mitigate the potential for increased run‐off and erosion, such treatments may also be detrimental to long‐term recovery of other native plant species. The degree to which seeded grasses dominate a site and reduce native plant diversity may be a function of the availability of resources such as nitrogen and light and differing abilities of native and seeded grasses to utilize available resources. We tested the hypothesis that seeded grasses have higher growth rates than native grasses when nitrogen and light availability is high in a greenhouse experiment. To determine how differing resource utilization strategies may affect distribution of native and seeded grasses across a burned landscape, we conducted botanical surveys after a wildfire in northern New Mexico, U.S.A., one and four years after the fire. In the greenhouse study we found seeded grasses to produce significantly more biomass than native grasses when nitrogen and light availability was high. Seeded grasses increased in cover from 1–4 years after the fire only in areas where total soil nitrogen was higher. Increased cover of seeded grasses did not affect recovery of native grasses, but it did lead to reduced native species richness at small scales. The potential negative long‐term consequences of seeding with exotic grasses should be considered in postfire rehabilitation treatments.     

Aboveground and Belowground Impacts Following Removal of the Invasive Species Baby's Breath (Gypsophila paniculata) on Lake Michigan Sand Dunes

The removal of invasive species is often one of the first steps in restoring degraded habitats. However, studies evaluating effectiveness of invasive species removal are often limited in spatial and temporal scale, and lack evaluation of both aboveground and belowground effects on diversity and key processes. In this study, we present results of a large 3‐year removal effort of the invasive species, Gypsophila paniculata, on sand dunes in northwest Michigan (USA). We measured G. paniculata abundance, plant species richness, plant community diversity, non‐native plant cover, abundance of Cirsium pitcheri (a federally threatened species endemic to this habitat), sand movement, arbuscular mycorrhizal spore abundance, and soil nutrients in fifteen 1000 m² plots yearly from 2007 to 2010 in order to evaluate the effectiveness of manual removal of this species on dune restoration. Gypsophila paniculata cover was greatly reduced by management, but was not entirely eliminated from the area. Removal of G. paniculata shifted plant community composition to more closely resemble target reference plant communities but had no effect on total plant diversity, C. pitcheri abundance, or other non‐native plant cover. Soil properties were generally unaffected by G. paniculata invasion or removal. The outlook is good for this restoration, as other non‐native species do not appear to be staging a “secondary” invasion of this habitat. However, the successional nature of sand dunes means that they are already highly invasible, stressing the need for regular monitoring to ensure that restoration progresses.     

Inoculation with native soil improves seedling survival and reduces non-native reinvasion in a grassland restoration

Losses of grasslands have been largely attributed to widespread land-use changes, such as conversion to row-crop agriculture. The remaining tallgrass prairie faces further losses due to biological invasions by non-native plant species, often with resultant ecosystem degradation. Of critical concern for conservation, restoration of native grasslands has been met with little success following eradication of non-native plants. In addition to the direct and indirect effects of non-native invasive plants on beneficial soil microbes, management practices targeting invasive species may also negatively affect subsequent restoration efforts. To assess mechanisms limiting germination and survival of native species and to improve native species establishment, we established six replicate plots of each of the following four treatments: (1) inoculated with freshly collected prairie soil with native seeds; (2) inoculated with steam-pasteurized soil with native seeds; (3) noninoculated with native seeds; or (4) noninoculated/nonseeded control. Inoculation with whole soil did not improve seed germination; however, addition of whole soil significantly improved native species survival, compared to pasteurized soil or noninoculated treatments. Inoculation with whole soil significantly decreased reestablishment of non-native invasive Bothriochloa bladhii (Caucasian bluestem); at the end of the growing season, plots receiving whole soil consisted of approximately 30% B. bladhii cover, compared to approximately 80% in plots receiving no soil inoculum. Our results suggest invasion and eradication efforts negatively affect arbuscular mycorrhizal hyphal and spore abundances and soil aggregate stability, and inoculation with locally adapted soil microbial communities can improve metrics of restoration success, including plant species richness and diversity, while decreasing reinvasion by non-native species.     

Response to soil biota by native, introduced non-pest, and pest grass species: is responsiveness a mechanism for invasion?

Soil biota have been credited with helping to maintain native plant diversity in multiple systems. Recent evidence suggests that introduced species may be less responsive to soil communities than most native species. If response to soil communities is correlated with invasive ability, we predict that introduced pest species should be less responsive to soil communities than introduced non-pest species or natives. In this study we test whether response to soil biota from two diverse grassland communities differs between four introduced pest, six introduced non-pest, and five native species in grasses in Yolo County, California. We found no variation in plant size or response to soil biota between introduced pest and introduced non-pest species, and these were combined in subsequent analyses. Overall, all introduced species grew significantly faster than native species. Native species showed greater variation in response to soil communities than both groups of introduced species, and native species’ response varied with soil community. Variation among native species’ response to soil nutrients and biota through processes like soil feedbacks may be key to maintaining diversity across landscapes in uninvaded environments. Introduced species appear less responsive to landscape variability in soil communities, which may allow them to establish and dominate plant communities in multiple habitats.