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Ecological communities often exhibit greater resistance to biological invasions when these communities consist of species that are not closely related. The effective size of this resistance, however, varies geographically. Here we investigate the drivers of this heterogeneity in the context of known contributions of native trees to the resistance of forests in the eastern United States of America to plant invasions. Using 42,626 spatially referenced forest community observations, we quantified spatial heterogeneity in relationships between evolutionary relatedness amongst native trees and both invasive plant species richness and cover. We then modelled the variability amongst the 91 ecological sections of our study area in the slopes of these relationships in response to three factors known to affect invasion and evolutionary relationships - environmental harshness (as estimated via tree height), relative tree density and environmental variability. Invasive species richness and cover declined in plots having less evolutionarily related native trees. The degree to which they did, however, varied considerably amongst ecological sections. This variability was explained by an ecological section's mean maximum tree height and, to a lesser degree, SD in maximum tree height (R2 GLMM = 0.47 to 0.63). In general, less evolutionarily related native tree communities better resisted overall plant invasions in less harsh forests and in forests where the degree of harshness was more homogenous. These findings can guide future investigations aimed at identifying the mechanisms by which evolutionary relatedness of native species affects exotic species invasions and the environmental conditions under which these effects are most pronounced. [ABSTRACT FROM AUTHOR]

We conducted a three-year field experiment to determine if amending soils with mulched European buckthorn (Rhamnus cathartica) can limit reinvasion, and whether two methods of incorporation--tilling or surface application--produce similar results. Mulch (a high carbon:nitrogen [C:N] material) may reduce reinvasion by stimulating soil microbial immobilization of N. Converting the woody waste generated during buckthorn removal into mulch would also eliminate both the need to remove this waste from restoration sites and the expense of acquiring amendments from elsewhere. We found that adding buckthorn mulch to soils, whether tilled or not, did not decrease either buckthorn reinvasion or soil N availability. The mechanical disturbance of tilling, however, caused a large, prolonged reduction in reinvasion by killing a previously unrecognized but major contributor to reinvasion--small buckthorn individuals (most < 5 cm tall) that were undetected during initial removal. Recruitment of new individuals occurred during the experiment, but recruitment rate decreased rapidly over time, suggesting that buckthorn seeds are short-lived. Three major recommendations emerge: (1) buckthorn mulch should not be used to limit reinvasion; (2) tilling can greatly reduce reinvasion by killing buckthorn individuals that are undetected during initial removal; and (3) because buckthorn seeds appear to be short-lived, reinvasion can be reduced by repeated, annual follow-up control of undetected and newly recruited individuals. [ABSTRACT FROM AUTHOR]

Invasive perennial species are frequently a barrier to native plant establishment in fertile sedge meadow wetland restorations. Amending soils with high carbon-to-nitrogen (C:N) materials may deplete nitrogen (N) and limit the establishment of invasive species, although the effectiveness of such amendments at depleting soil N in restored wetlands is largely unknown. Therefore we incorporated four high C:N materials (cedar, white pine, and red oak sawdust, as well as sucrose) into the soils of nonvegetated plots in a restored sedge meadow wetland and measured soil ammonium-N and nitrateN in relation to nonamended control plots over a 25-week period. All amendments depleted nitrate-N concentrations equivalently (67%-100%), although both the timing and the duration of this depletion varied among amendments. White pine sawdust was most effective, depleting nitrate-N for the entire 25 weeks. Sawdust from red oak and cedar depleted nitrate-N after 5 and 13 weeks, respectively. Lowered nitrate-N concentrations then persisted for the remaining 20 weeks in the red oak treatments, while the effects of cedar were short-lived (8 weeks). Sucrose depleted nitrate-N for 13 weeks. No amendment depleted ammonium-N concentrations, although cedar sawdust caused initial ammonium-N concentrations to increase by 300%-700%. Based on our findings, white pine sawdust will be more likely to deplete N effectively during the establishment of sedge meadow wetlands. It is unknown, however, if this depletion will suppress invasive perennials long enough to allow desired native species to establish a closed canopy and take up nitrogen, thereby limiting the chances of future invasions. [ABSTRACT FROM AUTHOR]

Efforts to eradicate invasive plants in restorations can unintentionally create conditions that favor reinvasion over the establishment of desired species, especially when remnant invasive propagules persist. Reducing resources needed by the invader for seedling establishment, however, may be an effective strategy to prevent reinvasion. Propagules of Phalaris arundinacea persist after removal from sedge meadow wetlands and reestablish quickly in posteradication conditions, hindering community restoration. A study was conducted in two experimental wetlands with controlled hydrologic regimes to determine if reducing light by sowing short-lived, nonpersistent native cover crops or immobilizing soil N by incorporating soil–sawdust amendments can prevent Phalaris reinvasion, allowing native communities to recover. A 10-species perennial target community and Phalaris were sown with high-diversity, low-diversity, or no cover crops in soils with or without sawdust, and seedling emergence, establishment, and growth were measured. High-diversity cover crops reduced light, decreasing Phalaris and target community seedling establishment by 89 and 57%, respectively. Short-term nitrogen reduction in sawdust-amended soils delayed Phalaris seedling emergence and decreased Phalaris seedling establishment by 59% but did not affect total target community seedling establishment. The target community reduced Phalaris seedling establishment as effectively as cover crops did. In plots where the target community was grown, amending soils with sawdust further reduced Phalaris seedling growth but not establishment. Results show that use of cover crops can reduce seedling establishment of desired species and is counterproductive to restoration goals. Further, establishing target species is more important and practical for limiting Phalaris reinvasion than is immobilizing nitrogen. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Invasive species occurrence is often related to the anthropogenic context of a given area. Quantifying the effects of roads is of particular interest as roads are a major vector for invasion. Our objective was to further quantify the effects of roads on forest plant invasion through a macroscale, high‐resolution investigation to assist effective invasion control and mitigation. Location: Eastern United States. Methods: Using invasive plant data from 23,039 forest inventory plots in 13 ecological provinces, we employed logistic regression to relate the odds of invasion to distance from a road, with adjustments for broadscale differences attributable to ecological provinces, and local scale differences in productivity, forest fragmentation and land use. Results: The overall proportion (P) of invaded plots was 0.58 (0.65 for plots within 50 m of a road), and the highest odds (P/1 − P) of invasion were found in relatively more productive, fragmented forest in landscapes with more than 10% agriculture or developed land cover. Wald chi‐square statistics indicated the best predictor of the odds of invasion was ecological province, followed by land use, productivity, forest fragmentation and distance from a road. Depending on the province, the adjusted odds of invasion decreased by up to 23% (typically 4%–10%) per 100 m distance from a road. The adjusted probability of invasion approached zero in only three provinces, for the least productive, least fragmented forest that was at least 2,000 m from a road in landscapes with less than 10% agricultural or developed land cover. Main conclusions: In the eastern United States, the existence of a nearby road is less important than the landscape context associated with the road. A purely road‐mediated effect has little practical meaning because anthropogenic activities and roads are pervasive and confounded. [ABSTRACT FROM AUTHOR]

Early detection and eradication of invasive plants are more cost-effective than managing well-established invasive plant populations and their impacts. However, there is high uncertainty around which taxa are likely to become invasive in a given area. Horizon scanning that combines a data-driven approach with rapid risk assessment and consensus building among experts can help identify invasion threats. We performed a horizon scan of potential invasive plant threats to Florida, USA--a state with a high influx of introduced species, conditions that are generally favorable for plant establishment, and a history of negative impacts from invasive plants. We began with an initial list of 2128 non-native plant taxa that are known invaders or crop pests. We built on previous invasive species horizon scans by developing databased criteria to prioritize 100 taxa for rapid risk assessment. The semi-automated prioritization process included selecting taxa "on the horizon" (i.e., not yet in the target location and not on a noxious weed list) with climate matching, naturalization history, "weediness" record, and global commonness. We derived overall invasion risk scores with rapid risk assessment by evaluating the likelihood of each of the taxa arriving, establishing, and having an impact in Florida. Then, following a consensus-building discussion, we identified six plant taxa as high risk, with overall risk scores ranging from 75 to 100 out of a possible 125. The six taxa are globally distributed, easily transported to new areas, found in regions with climates similar to Florida's, and can impact native plant communities, human health, or agriculture. Finally, we evaluated our initial and final lists for potential biases. Assessors tended to assign higher risk scores to taxa that had more available information. In addition, we identified biases towards four plant families and certain geographical regions of origin. Our horizon scan approach identified taxa conforming to metrics of high invasion risk and used a methodology refined for plants that can be applied to other locations. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Much is known about the elevational diversity patterns of native species and about the mechanisms that drive these patterns. A similar level of understanding is needed for non‐native species. Using published data, we examine elevational diversity patterns of non‐native plants and compare the resulting patterns with those observed for native plants. Location: Global. Methods: We compiled data from 65 case studies on elevational diversity patterns of non‐native plants around the world (including 32 cases in which both non‐native and native plants were sampled). We compared the elevational distributions (upper and lower limits, and extents) and diversity patterns of non‐native and native species. Results: Compared to native plant species, the elevational diversity patterns of non‐native plant species were more negative (47% vs. 13%) and less unimodal (44% vs. 84%). That is, non‐native species richness tended to be highest at lower elevations, whereas native species richness peaked at mid‐elevations. In cases where species richness for both non‐native and native species on the same mountains showed unimodal patterns in relation to elevation, maximum values in species richness occurred at lower elevations for non‐native species. Main conclusions: At present levels of invasion, non‐native and native species show different patterns in both distribution and diversity along elevational gradients worldwide. However, our observations constitute a snapshot of ongoing, long‐term invasion processes. As non‐native species typically show strong associations with human activities, future changes in human population (e.g. growth and migration), land use and climate change may promote upward spread of non‐native species and may thus increase risks of impact on native species and communities. [ABSTRACT FROM AUTHOR]

Over the last few decades, considerable attention has focused on small-scale studies of invasive plants and invaded systems. Unfortunately, small scale studies rarely provide comprehensive insight into the complexities of biological invasions at macroscales. Systematic and repeated monitoring of biological invasions at broad scales are rare. In this report, we highlight a unique invasive plant database from the national Forest Inventory and Analysis (FIA) program of the United States Forest Service. We demonstrate the importance and capability of this subcontinental-wide database by showcasing several critical macroscale invasion patterns that have emerged from its initial analysis: (1) large portion of the forests systems (39%) in the United States are impacted by invasive plants, (2) forests in the eastern United States harbor more invasive species than the western regions, (3) human land-use legacies at regional to national scales may drive large-scale invasion patterns. This accumulated dataset, which continues to grow in temporal richness with repeated measurements, will allow the understanding of invasion patterns and processes at multi-spatial and temporal scales. Such insights are not possible from smaller-scale studies, illustrating the benefit that can be gained by invasion monitoring programs elsewhere. [ABSTRACT FROM AUTHOR]

• Urban stormwater ponds used to manage runoff could facilitate plant invasion. • We identified over 76,000 stormwater ponds across Florida, US. • Ponds in Gainesville, FL harbor high richness and cover of invasive plants. • Invasion severity is highest in temporary ponds with little to no management. • Results highlight the commonality and disservices of these designed ecosystems. Designed ecosystems are built as part of ongoing urban expansion, providing a suite of valued ecosystem services. However, these new ecosystems could also promote disservices by facilitating the colonization and spread of invasive species. We conduct the first assessment of the quantity and invasion of an overlooked designed ecosystem: stormwater ponds. These ponds are commonly recommended for managing urban hydrology, but little is known about their ecology or extent of proliferation. Using a broad-scale survey of pond coverage in Florida, USA, we found that over 76,000 stormwater ponds have been built just in this state, forming 2.7% of total urban land cover. This extensive pondscape of manufactured habitats could facilitate species spread throughout urban areas and into nearby natural waterbodies. We also conducted a survey of the severity of plant invasion in 30 ponds in Gainesville, FL, US across two pond types (dry vs. wet), and a gradient of management intensities (low, medium, high) and pond ages. We unexpectedly found a high number of invasive plant species (28 in just 30 ponds). Ninety-six percent of surveyed ponds contained from one to ten of these species, with ponds exhibiting high turnover in invader composition (i.e., high beta diversity). The bank sections of dry unmanaged ponds exhibited the highest mean invasive species richness (5.8 ± 1.3) and the inundated centers of wet medium managed ponds exhibited the highest mean invasive species cover (34 ± 12%). Invasive plant richness and cover also tended to be greater in dry ponds with higher soil nutrient levels, and in older wet ponds. Therefore, we found that highly maintained and younger wet ponds were the least invaded. Nevertheless, common management practices that limit plant invasions may also limit native species establishment and invasion may increase in the decades following pond construction. [ABSTRACT FROM AUTHOR]