Non-native Plant Invasions Research Articles

The UF/IFAS Assessment of Nonnative Plants in Florida's Natural Areas: History, Purpose, and Use

Nonnative invasive plant species pose a significant threat to Florida’s natural areas. The UF/IFAS Assessment of Nonnative Plants in Florida’s Natural Areas uses literature-based risk assessment tools to predict the invasion risk of both nonnative species that occur in the state as well as species proposed for introduction. The UF/IFAS Assessment team has evaluated more than 900 species, including 208 species proposed for introduction or new uses. The team is actively identifying and evaluating potentially problematic nonnative species (and sub-specific or hybrid taxa). Recommendations and supporting information from the UF/IFAS Assessment can be found at http://assessment.ifas.ufl.edu.

Role of Horses as Potential Vectors of Non-Native Plant Invasion: An Overview

Non-native plant invasions can lead to staggering ecological and economic costs. Thus, land managers are concerned about vectors of seed and propagule introduction onto public lands. Because horses are one of several potential vectors of non-native seed dispersal, we summarize and interpret existing literature and identify potential impacts of horse use on non-native plant spread in natural areas. Several studies indicate non-native seeds can germinate after digestion by horses. In addition to their ability to carry viable non-native seeds in their feces, the literature indicates horses can trample native vegetation, cause soil disturbance, and increase soil nitrogen availability in some habitats. The combination of disturbance, which is known to increase invasibility, and introduction of seeds in horse feces could promote non-native plant invasions in wildlands. However, in situ studies have not demonstrated direct causal links between horses and plant invasions. More research is required to determine where, and to what extent, establishment and spread of non-natives occurs in situ as a direct result of disturbances and seed introduction by horses. Guidelines or regulations regarding horse use already exist in some recreational areas. Where none exist, we recommend development of best management practices, such as weed education programs for equestrians, use of Certified Weed Free Feed, and placement of manure bunkers at horse camps and trailheads.Lauren D. Quinn, Adda Quinn, Mietek Kolipinski, Bonnie Davis, Connie Berto, Mark Orcholski, and Sibdas Ghosh. 2010. “Role of Horses as Potential Vectors of Non-Native Plant Invasion: An Overview.” Natural Areas Journal 30(4):408-416

Allelopathic effects of switchgrass on redroot pigweed and crabgrass growth

Non-native invasive plant species influence plant community composition and competitively eradicate native species. However, there is doubt regarding how global invasive species increase and explosively interfere with native plants. Invasive plants always have strong allelopathic potential. In this study, allelopathic effects of switchgrass on redroot pigweed and crabgrass growth were investigated by field and laboratory experiments. Within a 0.4-m distance of switchgrass, density and shoot biomass of native species were significantly suppressed in the field, with 95.1% and 93.0% inhibition on density of redroot pigweed and crabgrass and with 99.0% and 97.7% inhibition on shoot biomass, respectively, during the third growing season. Significant inhibitory effects on shoot and root biomass were observed at the 5:5 (switchgrass–native species) proportion in glass bottles, by 41.57% and 51.21% for shoot and root biomass of redroot pigweed and by 33.42% and 56.95% for shoot and root biomass of crabgrass, respectively. Results of a glass bottle experiment showed that shoot and root biomass of redroot pigweed and crabgrass could be significantly inhibited by contact with switchgrass root. Results of a Petri dish experiment showed that aqueous extracts of switchgrass significantly inhibited germination process of both species at high concentrations, with 90.74% and 18.62% inhibition on germination rate and plumule length of redroot pigweed and with 63.59%, 16.38%, and 19.92% inhibition on germination rate, plumule, and radicle lengths of crabgrass, respectively, at the concentration of 0.1 g·mL−1. This report demonstrated that switchgrass had allelopathic effects on redroot pigweed and crabgrass growth.

Non-Invasive Characterization of Single-, Double- and Triple-Viral Diseases of Wheat With a Hand-Held Raman Spectrometer.

Plant diseases can reduce crop yield by up to 100%. Therefore, timely and confirmatory diagnosis of plant diseases is strongly desired. Typical pathogen assaying methods include polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). These approaches are quite useful but are also time-consuming and destructive to the sample. Raman spectroscopy (RS) is a modern analytical technique that enables non-invasive plant disease detection. In this study, we report on Raman-based detection of wheat diseases caused by wheat streak mosaic virus (WSMV) and barley yellow dwarf virus (BYDV). Our results show that RS can be used to differentiate between healthy wheat and wheat infected by these two viruses. We also show that RS can be used to identify whether wheat is infected by these individual viruses or by a combination of WSMV and BYDV, as well as WSMV, BYDV, and Triticum mosaic virus (TriMV). We found that wheat spectra showed non-linear spectroscopic responses to coinfection by different viruses. These results suggest that RS can be used to probe pathogen-specific changes in plant metabolism. The portable nature of this approach opens the possibility of RS directly in the field for confirmatory diagnostics of viral diseases.

The influence of warming and biotic interactions on the potential for range expansion of native and nonnative species.

Plant species ranges are expected to shift in response to climate change, however, it is unclear how species interactions will affect range shifts. Because of the potential for enemy release of invasive nonnative plant species from species-specific soil pathogens, invasive plants may be able to shift ranges more readily than native plant species. Additionally, changing climatic conditions may alter soil microbial functioning, affecting plant–microbe interactions. We evaluated the effects of site, plant–soil microbe interactions, altered climate, and their interactions on the growth and germination of three congeneric shrub species, two native to southern and central Florida (Eugenia foetida and E. axillaris), and one nonnative invasive from south America (E. uniflora). We measured germination and biomass for these plant species in growth chambers grown under live and sterile soils from two sites within their current range, and one site in their expected range, simulating current (2010) and predicted future (2050) spring growing season temperatures in the new range. Soil microbes (microscopic bacteria, fungi, viruses and other organisms) had a net negative effect on the invasive plant, E. uniflora, across all sites and temperature treatments. This negative response to soil microbes suggests that E. uniflora’s invasive success and potential for range expansion are due to other contributing factors, e.g. higher germination and growth relative to native Eugenia. The effect of soil microbes on the native species depended on the geographic provenance of the microbes, and this may influence range expansion of these native species.

Songbird Use of Native and Invasive Fruit in the Northeastern USA

ABSTRACTFruit is consumed by songbirds, yet whether or not it comprises an important component of habitat quality depends on the extent to which it is used by birds. In addition, there is evidence fruits of exotic invasive species may be nutritionally inferior to fruits of native species, so the influence of plant invasion on bird body condition is of interest to managers. Birds that consume invasive fruits may also serve as seed vectors, and consumption of fruits of invasive species may exacerbate invasion. Thus, the extent to which songbirds consume fruits of native versus invasive plant species, influence of plant invasion on bird body condition, and extent to which birds exhibit foraging behaviors that elevate their potential to act as dispersers of invasive species have important implications for habitat management. To understand bird use of native and invasive fruits and the potential role of birds in dispersing invasive plants, we observed bird foraging, measured body condition indices of birds captured in mist nets, measured available fruits of native and invasive plants, and calculated indices of seed dispersal for bird species based on fruit handling and consumption, within 16 shrubland sites in western Massachusetts, USA. Our findings indicate that birds use fruit extensively (57% of foraging events), use varied among species, and frugivorous species at our sites generally chose the fruit of native species, especially Prunus, over fruits of invasive species. Body condition indices were negatively related to the proportion of invasive fruit in most cases. In general, birds were better dispersers for native fruits than for invasive fruits. Our findings support the value of native fruit resources as a component of habitat quality, and, conversely, suggest that nonnative plant invasion may lead to reduced habitat quality for songbirds. © 2020 The Wildlife Society.

Habitat and soil associations of a fossorial toad in a Sonoran Desert riparian forest

Despite occupying small land areas, riparian systems provision a large number of vertebrates, including amphibians, one of the most threatened vertebrate taxa. We associated capture rates of a fossorial desert anuran (Scaphiopus couchii) to non-native plant invasion and shrub encroachment via soil traits and habitat physiognomy in native, invaded, and shrub-encroached riparian habitats in the Sonoran Desert. We measured habitat and anurans at 18 sites along the San Pedro and Gila Rivers in three stand types based on dominant trees, cottonwood-willow forest (Populus-Salix), mesquite woodland (Prosopis), and non-native saltcedar stands (Tamarix). Dominant tree species were useful descriptors of habitat physiognomy. Spadefoots were associated with xeroriparian habitat at Prosopis sites and nearly absent from Tamarix sites. Soil moisture and texture heavily influenced spadefoot partitioning across forest types. Altering in-stream flow has modified riparian areas by causing xerification, Prosopis expansion, and proliferation of non-native species. The effects of Prosopis encroachment on this fossorial anuran may be less than Tamarix invasion, which could be deleterious to many anurans. We suggest monitoring vulnerable amphibians and conservation measures to preserve native riparian habitat.

Computer Vision and Spectral Analysis Technologies for Non-Invasive Plant Studying

Computer vision and spectral analysis of digital images are technologies that allow the use of automated and robotic systems for non-invasive plant studying, production and harvesting of agricultural products, phenotyping and selection of new plant species. (Research purpose) The research purpose is in analyzing the application of modern digital non-invasive methods of plant research using computer (technical) vision and prospects for their implementation. (Materials and methods) Authors have reviewed the works on the use of non-invasive methods for obtaining information about the state of plants. The article presents classification and analyze of the collected materials according to the criteria for collecting and analyzing digital data, the scope of application and prospects for implementation. Authors used the methods of a systematic approach to the research problem. (Results and discussion) The article presents the main directions of using computer vision systems and digital image analysis. The use of computer vision technologies in plant phenotyping and selection reduces the labor cost of research, allowing the formation of digital databases with a clear structure and classification by morphological features. It was found that the introduction of neural networks in the process of digital image processing increases the accuracy of plant recognition up to 99.9 percent, and infectious diseases up to 80 percent on average. (Conclusions) The article shows that in studies using hyperspectral optical cameras and sensors are used cameras with an optical range from 400 to 1000 nanometers, and in rare cases, hyperspectral camera systems with a total coverage of the optical range from 350 to 2000 nanometers. These optical systems are mainly installed on unmanned aerial vehicles to determine vegetation indices, foci of infection and the fertility of agricultural fields. It was found that computer vision systems with hyperspectral cameras could be used in conjunction with fluorescent plant markers, which makes it possible to solve complex problems of crop recognition without involving computational resources.

Disease in Invasive Plant Populations.

Non-native invasive plants can establish in natural areas, where they can be ecologically damaging and costly to manage. Like cultivated plants, invasive plants can experience a relatively disease-free period upon introduction and accumulate pathogens over time. Diseases of invasive plant populations are infrequently studied compared to diseases of agriculture, forestry, and even native plant populations. We evaluated similarities and differences in the processes that are likely to affect pathogen accumulation and disease in invasive plants compared to cultivated plants, which are the dominant focus of the field of plant pathology. Invasive plants experience more genetic, biotic, and abiotic variation across space and over time than cultivated plants, which is expected to stabilize the ecological and evolutionary dynamics of interactions with pathogens and possibly weaken the efficacy of infectious disease in their control. Although disease is expected to be context dependent, the widespread distribution of invasive plants makes them important pathogen reservoirs. Research on invasive plant diseases can both protect crops and help manage invasive plant populations.

Biogeographical comparison of terrestrial invertebrates and trophic feeding guilds in the native and invasive ranges of Carpobrotus edulis

Plant invasions impact on biodiversity by altering the composition of native communities by disrupting taxonomic and functional diversity. Non-native plants are often released from their natural enemies, which might result in a reduction of the attack of primary consumers. However, they can also be exposed to the attack of new herbivores that they might not be able to tolerate. Hence, invertebrate communities can be influenced by invasive non-native plants, which in turn modify interactions and change environmental conditions. In this study, we examined the compositional and trophic diversity of invertebrate species, comparing ecosystems with and without the plant species Carpobrotus edulis in coastal areas in its native (South Africa) and introduced (Iberian Peninsula) ranges. Results show that C. edulis has a clear impact on invertebrate communities in its non-native range, reducing their abundance in invaded areas, and particularly affecting certain trophic groups. Invasive C. edulis also alters the invertebrate diversity by not only reducing abundance but also by altering species composition. Overall, the physical dominance of C. edulis modifies the co-occurrence of invertebrate assemblages, reducing the number of trophic groups and leading to substantial effects on primary consumers. Results suggest that the lack of natural enemies might be an important driver of the expansion of C. edulis in its introduced range. Further work is needed to examine long-term changes caused by non-native plants on invertebrate assemblages and the subsequent modification of biological interactions.

Temperate deciduous forests embedded across developed landscapes: Younger forests harbour invasive plants and urban forests maintain native plants

Abstract Temperate deciduous forests in the United States are located in the most densely populated states across the northern and mid-Atlantic east coast. Land development and associated human activities result in small forests that are susceptible to anthropogenic influences, such as urbanization and non-native plant invasion. The overall objective of this study was to assess spatial and temporal drivers of forest vegetation structure and diversity in small forests embedded across developed landscapes. We assessed woody plant composition across spatial gradients (i.e., urbanization and non-native plant invasion) and a temporal gradient (i.e., time since canopy closure) across 38 forests along the east coast of the United States in northern Delaware and southeastern Pennsylvania. Surprisingly, we found the invasion gradient was not related to the urban gradient across our forests. Across all forests, the canopy consisted of native species (98% of all trees), whereas the forest understory was most vulnerable to non-native plant invasion (65% of all woody plant stems). Greater native species richness in forest canopies and understories with increasing urbanization supports the conclusion that urban forests maintain native species and are not inherently degraded ecosystems. Non-native plant invasion has a strong influence on understory plant communities, and the duration of intact forest canopy had a strong negative correlation with non-native plant invasion suggesting intact forests can resist invasion. Synthesis. This is the first study to compare simultaneously the importance of invasion and urbanization in determining plant community composition in forests embedded across developed landscapes, and to discover that younger forests harbor more invasive plants and urban forests maintain native plants.

Assessment of the Female Fertility of 26 Commercial Lantana camara Cultivars and Six Experimental Lines

Lantana camara is an important plant for the environmental horticultural industry, yet it can be invasive, cross-pollinating with native lantana and dispersing fruit (and seeds) to natural and agricultural lands. Identification and development of sterile cultivars is much needed to meet industry and consumer needs for noninvasive plant materials. Previously we evaluated the male fertility of 32 L. camara cultivars/breeding lines at five ploidy levels. This study was to assess their female fertility and understand the relationship between female fertility and ploidy level and the production of unreduced female gametes (UFGs) in L. camara. These cultivars/breeding lines significantly varied in percent fruiting plants (6.3% to 100.0%), percent fruiting peduncles (0.3% to 98.8%), fruit per peduncle (0.003 to 7.173), seed germination (0% to 57.1%), and female fertility index (0.003 to 2.998). Certain diploids (e.g., ‘Denholm White’) were highly female-sterile. Eleven of the 13 triploids evaluated were UFG-producing and rather fertile. The two non-UFG-producing triploids had the female fertility index of 0.005, thus most sterile. Tetraploids, especially those producing UFGs, were prolific fruit producers. These results show that ploidy level and UFG production play a significant role in determining fruit (seed) production capacity and female fertility of L. camara. None of the commercial triploid cultivars evaluated reached desirable levels of male and female sterility, indicating a strong need to develop new lantana cultivars that are male- and female-sterile. Our results suggest that production and selection of triploids can be effective to sterilize L. camara, but it is imperative to select diploids and tetraploids that do not produce UFGs as the breeding parents.

Plant cover restoration to inhibit seedling emergence, growth or survival of an exotic invasive plant species

ABSTRACT We conducted a mesocosm restoration experiment to test the efficacy of early summer sowing of seed mixtures for inhibiting the emergence, growth and/or survival of giant hogweed (Heracleum mantegazzianum) seedlings. H. mantegazzianum is invasive in Europe and North America, where it has a negative effect on plant diversity and represents a serious health hazard, due to the photodermatitis it may cause. We tested five plant mixtures comprising a selection of North American native or naturalized non-invasive plant species. Compared to the unseeded control mesocosm, all plant covers reduced seedling emergence, growth and survival of H. mantegazzianum. There were large differences between mixtures regarding inhibition effects. The nature of the effects depended on species composition, with one mixture more effective in preventing establishment, another essentially affecting seedling growth and survival. Total plant cover, irrespective of seed mixtures, appeared to have a major effect on H. mantegazzianum. Other factors that may have played a role included the litter from the seeded plants and the allelopathic effect of Canada goldenrod (Solidago canadensis). Our study adds to the growing body of evidence promoting the restoration of a plant cover as a means to prevent reinfestation by invasive species following a control operation.

Lesser leaf herbivore damage and structural defense and greater nutrient concentrations for invasive alien plants: Evidence from 47 pairs of invasive and non-invasive plants

Empirical evidence of enemy release is still inconsistent for invasive alien plant species, although enemy release is the key assumption for both the enemy release hypothesis (ERH) and the evolution of increased competitive ability hypothesis (EICA). In addition, little effort has been made to test this assumption in terms of defense investment using a multi-species comparative approach. Using a phylogenetically controlled within-study meta-analytical approach, we compared leaf herbivore damage, structural defenses and nutrients between 47 pairs of invasive versus native and/or non-invasive alien plants in China. The invasive relative to the co-occurring native or non-invasive (native and non-invasive alien) plants incurred lesser leaf herbivore damage, had lesser leaf concentrations of cellulose, hemicellulose, lignin and carbon, lesser leaf density and carbon or lignin to nitrogen ratio but greater nutrients, which may facilitate success of the invasive plants. The lesser structural investment did not result in lesser leaf construction costs for the invaders, which may be associated with their greater leaf nitrogen concentration. However, the invasive plants were not significantly different from the non-invasive alien plants in any trait. Our results provide strong evidence for ERH, also are consistent with EICA, and indicate that enemy release may be an important factor in alien plant invasions.

Repeated, high-severity wildfire catalyzes invasion of non-native plant species in forests of the Klamath Mountains, northern California, USA

Non-native plant invasions are often catalyzed by wildfires and may alter the structure, function, and composition of ecosystems. Of particular concern are non-native annual grasses that promote increased fire frequency and compete with native vegetation for early season moisture. While these effects are well studied in non-forested ecosystems, relatively few studies document invasions of non-native annual grasses in forested ecosystems. We document non-native plant invasion following repeated high-severity wildfire in mixed-conifer/hardwood forests dominated by Douglas-fir (Pseudotsuga menziesii) in the Klamath Mountains of northern California. Despite great concern regarding the loss of conifer dominance and transitions to non-forested states related to recent and projected increases in wildfire activity, there is little known about invasions of non-native plant species following fire in this region. Non-native plant species capable of long-distance dispersal had an average total cover of 26% and were ubiquitous across a systematic, gridded sample of twenty 800 m2 plots. Non-native forbs included multiple species of common post-disturbance invaders (e.g. Cirsium vulgare, Senecio sylvaticus, Lactuca serriola). Non-native annual grasses comprised more of the vegetative cover than non-native forbs (17% vs. 9%), and were dominated by two species, Aira caryophyllea and Vulpia myuros, which reached as high as 80% cover. Our findings indicate that non-native annual grasses are a novel stressor that may accelerate projected loss of conifer dominance in the Klamath Mountains by facilitating fire spread and increasing competition for early season soil moisture. Additional monitoring will be crucial to understanding the impacts of non-native plants as fire activity in this region continues to increase.

Squeezed from All Sides: Urbanization, Invasive Species, and Climate Change Threaten Riparian Forest Buffers

Streamside forests of urbanizing coastal regions lie at the nexus of global changes: rising sea levels, increasing storm surge, expanding urban development, and invasive species. To understand how these combined stressors affect forest conditions, we identified forest patches adjacent to urban land, analyzed adjacent land cover, modeled forest inundation, and sampled 100 sites across the Chesapeake Bay and Delaware Bay watersheds. We found that the majority of forest patches are adjacent to urban land and projected flooding will affect 8–19% of regional forested land. We observed non-native invasive plants in 94% of forest plots. Trees were predominantly native, but over half of shrub stems were invasive species and more than 80% of plots contained invasive woody vines. Disturbance of human origin was correlated with abundance of invasive trees. Signs of deer activity were common. Richness and number of growth forms of invasive plants were related to adjacent agricultural land cover. These data reveal that streamside forests are impacted by the interacting stressors of urbanization, climate change, and invasive species spread. Our results emphasize the importance of protection and restoration of forests in urban regions and point to the need for a social-ecological systems approach to improve their condition.

Declines in native forb richness of an imperiled plant community across an anthropogenic nitrogen deposition gradient

AbstractAnthropogenic nitrogen (N) deposition is known to reduce plant diversity in ecosystems worldwide; however, effects on the diversity of Mediterranean‐type ecosystems—global hotspots of biodiversity—are relatively unexplored. In California, elevated N deposition due to air pollution has a multitude of ecological effects including the facilitation of nonnative plant invasion and altered ecosystem functioning, but impacts on plant richness have been inadequately quantified. We addressed this research gap by evaluating patterns of plant richness in coastal sage scrub (CSS), a severely threatened, highly diverse Mediterranean‐type shrubland, across the Santa Monica Mountains National Recreation Area. This is the largest urban national park in the United States and experiences a strong gradient of N deposition due to its proximity to urban Los Angeles. We measured soil N, plant cover, and richness at 30 CSS sites across this gradient and used regression analyses to explore relationships between richness, N deposition, and other environmental variables. We observed significant declines in plant richness across a steep gradient of soil N availability that paralleled patterns of N deposition, primarily due to decreases in native forb species. Our analyses identified soil N as the best predictor of patterns of native forb richness, but other factors, including nonnative plant cover and aridity, may also drive reduced richness. In addition to the marked decline in the number of native forb species, increasing N deposition was also associated with lower native shrub richness per area and increased cover of nonnatives. These results highlight the threat posed by N deposition to the conservation of this already imperiled ecosystem under continued environmental change.

Preliminary application of DNA barcoding toward the detection of viable plant propagules at an initial, international point-of-entry in Georgia, USA

Over 90% of global commercial trade occurs between seaports, which are initial points-of-entry for nonnative, potentially invasive propagules. As such, there is a need to develop means to both rapidly intercept and identify propagules as they arrive. Here, we focus on plant propagules that are assumed to be non-native, in seed form. Because standard morphological techniques alone are laborious and require taxonomic expertise, we sought to address if identification through barcoding of the plastid DNA (rbcL + matK genes) of plant seeds could improve current processes in the early detection and rapid response to prevent entry/establishment of nonnative plant species. This research conducted a preliminary foray to evaluate the utility of widely accepted plant plastid DNA barcodes to identify plant propagules (seeds, hereafter) collected from the air-intake grilles of refrigerated shipping containers of a single agricultural commodity arriving at the Port of Savannah, Georgia, USA. We ask four questions: (1) Can DNA barcoding be used to detect seeds collected from shipping containers at the port? (2) What is the genetic composition of propagules entering the port? (3) How do morphological identifications compare to those based on genetic analysis? (4) Are nonnative invasive plant species present on shipping containers entering the Port of Savannah? This research collected 11,044 seeds from 628 refrigerated shipping containers between 2015 and 2017. Seeds were then morphologically sorted into Seed Types. Barcoding of the matK and rbcL gene regions of the plastid genomes directly isolated from seeds resulted in poor amplification. This is likely due to a host of potential confounding factors. Therefore, we germinated seeds and utilized leaf-tissues for sequencing of these two gene regions. From BLASTn analyses, results returned top hits for a variety of species, with up to 22 possible nonnative plant species and one definite Federal Noxious Weed. This work investigates the interception application of DNA barcoding to improve agro- and bio-security issues posed by nonnative and invasive species. Though this study required the germination of the seeds to obtain leaf-tissue suitable for our DNA barcoding method, we effectively demonstrated seed viability. Our seed identification process was lengthy and understandably not feasible for real-time application. Therefore, we seek to improve our methods for future applications by testing other approaches that may better complement morphological identification. Next reasonable steps include improved extraction protocols, metabarcoding to generate DNA barcode sequences directly from groups of seeds harvested from shipping containers and implementing other next-generation sequencing techniques.

Community- and trophic-level responses of soil nematodes to removal of a non-native tree at different stages of invasion.

Success of invasive non-native plant species management is usually measured as changes in the abundance of the invasive plant species or native plant species following invader management, but more complex trophic responses to invader removal are often ignored or assumed. Moreover, the effects of invader removal at different stages of the invasion process is rarely evaluated, despite a growing recognition that invader impacts are density or stage-dependent. Therefore, the effectiveness of invasive species management for restoring community structure and function across trophic levels remains poorly understood. We determined how soil nematode diversity and community composition respond to removal of the globally invasive tree species Pinus contorta at different stages of invasion by reanalysing and expanding an earlier study including uninvaded vegetation (seedlings removed continuously), early invader removal (saplings removed), late removal (trees removed), and no removal (invaded). These treatments allowed us to evaluate the stage-dependent belowground trophic responses to biological invasion and removal. We found that invaded plots had half the nematode taxa richness compared to uninvaded plots, and that tree invasion altered the overall composition of the nematode community. Differences in nematode community composition between uninvaded nematode communities and those under the tree removal strategy tended to dilute higher up the food chain, whereas the composition of uninvaded vs. sapling removal strategies did not differ significantly. Conversely, the composition of invaded compared to uninvaded nematode communities differed across all trophic levels, altering the community structure and function. Specifically, invaded communities were structurally simplified compared to uninvaded communities, and had a higher proportion of short life cycle nematodes, characteristic of disturbed environments. We demonstrate that a shift in management strategies for a globally invasive tree species from removing trees to earlier removal of saplings is needed for maintaining the composition and structure of soil nematode communities to resemble uninvaded conditions.

Which Traits Make Weeds More Successful in Maize Crops? Insights from a Three-Decade Monitoring in France.

A major aim in invasion biology is identifying traits distinguishing alien invasive and alien non-invasive plants. Surprisingly, this approach has been, so far, poorly used to understand why some arable weeds are abundant and widespread while others are rare and narrowly distributed. In the present study, we focused on the characteristics of successful weeds occurring in maize fields, one of the most important crops worldwide. Two national weed surveys conducted in France were used to identify increasing and decreasing species based on 175 and 484 surveyed fields in the 1970s and the 2000s, respectively. Weed trait values related to regional frequency, local abundance, and specialization to maize were identified with phylogenetic generalized least-squares (PGLS). We found a positive relationship between regional frequency and local abundance, i.e., the most widespread weeds were also locally more abundant. We highlighted that weeds with the C4 photosynthetic pathway and summer emergence were more abundant, more frequent, and more specialized to maize crops. More generally, we highlighted two successful strategies: On the one hand, traits related to a general weediness syndrome with rapid resource acquisition (high SLA and Ellenberg-N) and high colonization capacity (seed longevity, fecundity, and wind dispersal); on the other hand, traits related to specific adaptation to spring cultivation (thermophilous species with summer emergence, late flowering, and C4 photosynthetic pathway). Deviations from the abundancy–frequency relationships also indicated that species of the Panicoideae sub-family, species with Triazine-resistant populations, and neophyte species were more abundant than expected by their regional frequency. To some extent, it is therefore possible to predict which species can be troublesome in maize crops and use this information in weed risk assessment tools to prevent new introductions or favor early detection and eradication. This study showed how tools developed in functional and macro-ecology can be used to improve our understanding of weed ecology and to develop more preventive management strategies.