Spread Of Non-native Plants Research Articles

Hidden cargo: The impact of historical shipping trade on the recent-past and contemporary non-native flora of northeastern United States.

Understanding establishment and spread of non-native plants is important in the face of a homogenizing global flora. While many studies focus on successful, invasive species, fewer have studied failed plant introductions. Until the early 1900s, large quantities of ship ballast, often containing foreign plant propagules, were deposited in New Jersey (USA). The resulting ballast flora is documented in extensive herbarium records, providing us a unique opportunity to analyze successes and failures of novel plant species introductions. We used digitized specimens from 75 herbaria to study 264 non-native species introduced into New Jersey through 19th century ballast deposition. We used spatial (density-based clustering; HDBSCAN) and temporal analyses of species retention and geographic spread to quantify disappearance rate, survival, and dispersion through time and define trajectory groups. Four distinct trajectory groups were identified: waif (only present during import; 32% of species), short-term (disappeared quickly; 20%), established-limited spread (survives locally, 30%), and established-widespread (widespread, 18%). Species disappearance rate was highest during ballast deposition and decreased soon after deposition stopped around 1900. Spatial patterns showed a strong association with 19th century railroads for inland dispersal from ports. The disappearance rate and spatial analyses are robust to herbarium collection bias. This study using New Jersey as a model is one of the few documenting multispecies successes and failures in inadvertent plant introductions. Results reveal distinct trends in species establishment and geographic spread and highlight the utility of herbarium specimens in answering questions that span large time scales.

The Influence of Management Regimes and Habitat Characteristics on the Persistence and Current Occupancy of the Non-Native Melinis repens (Natalgrass)

Although prescribed fires and pre-treatments (e.g., roller chopping and mowing) are used by public and private landowners to manage natural habitats in Florida, they can influence the invasion and spread of non-native plants in natural areas. Firelanes and roads used to access habitat for management practices create corridors for invasive grasses. Melinis repens (Natalgrass) is an invasive plant found throughout Florida. Fire regimes and roads acting as corridors may affect invasion and persistence of Natalgrass, but these topics have not been well-studied. Following up on distribution data originally collected in 2002 at Archbold Biological Station, we explored how fire regimes, distance to road, habitat type, and microhabitat factors influenced Natalgrass persistence through 2016, and current Natalgrass occupancy. Persistence from 2002–2016 was not influenced by distance to road. However, Natalgrass was currently more likely to occupy habitat closest to roads and was more likely to persist in areas burned within 16 y. Although Natalgrass was most likely to persist in human modified habitat, it still persisted in and occupied interior scrub habitat. Natalgrass was more likely to occupy areas with lower litter, shrub, and palmetto cover, which are characteristics of many habitats, including sandy roadsides and recently burned scrub habitat. These results suggest Natalgrass is able to persist in habitats other than roads, and distance to road did not influence its persistence; thus, land managers should treat interior habitat where Natalgrass is persisting. At the same time, searches for new populations of Natalgrass should be focused largely in areas close to corridors, such as in roads and firelanes.

Plant invasions into mountains and alpine ecosystems: current status and future challenges

Recent years have seen a surge of interest in understanding patterns and processes of plant invasions into mountains. Here, we synthesise current knowledge about the spread of non-native plants along elevation gradients, emphasising the current status and impacts that these species have in alpine ecosystems. Globally, invasions along elevation gradients are influenced by propagule availability, environmental constraints on population growth, evolutionary change and biotic interactions. The highest elevations are so far relatively free from non-native plants. Nonetheless, in total nearly 200 non-native plant species have been recorded from alpine environments around the world. However, we identified only three species as specifically cold-adapted, with the overwhelming majority having their centres of distribution under warmer environments, and few have substantial impacts on native communities. A combination of low propagule availability and low invasibility likely explain why alpine environments host few non-native plants relative to lowland ecosystems. However, experiences in some areas demonstrate that alpine ecosystems are not inherently resistant to invasions. Furthermore, they will face increasing pressure from the introduction of pre-adapted species, climate change, and the range expansion of native species, which are already causing concern in some areas. Nonetheless, because they are still relatively free from non-native plants, preventative action could be an effective way to limit future impacts of invasions in alpine environments.

Strategies for restoring tree seedling recruitment in high conservation value tropical montane forests underplanted with cardamom

Question What strategies are most appropriate for restoring tree seedling recruitment whilst avoiding the spread of invasive plant species in high conservation value tropical forests disturbed by planting a shade-demanding crop? Location Knuckles Forest Reserve, Sri Lanka (7°21′–7°24′ N, 80°45′–80°48′ E). Methods An experiment was conducted to test the effects of clipping or removal of established cardamom plants on recruitment of native tree seedlings and spread of non-native plants in a tropical montane forest with abandoned cardamom stands in the understorey. The number and composition of tree seedling emergents, the cover of herbaceous plants and the recovery of cardamom were assessed for 3 yr. Results Tree seedling recruitment was higher in plots from which above-ground cardamom biomass had been removed through slashing (mean ± SE per 5 m2; 28.9 ± 2.70) and those where cardamom plants had been removed completely through uprooting (32.2 ± 3.17), or when dead cardamom leaves and stems were removed with small-scale extraction of pods (22.5 ± 2.16), than in unmanipulated control plots (16.6 ± 1.13) over 15 mo. The species composition of tree seedling emergents did not differ in response to removal of cardamom. However, the cover of herbaceous plants, including the non-native invasive Ageratina riparia, increased in response to removal of cardamom. Recovery of cardamom was higher when the plants had been slashed than when entire plants were uprooted and removed. Conclusion Slashing or uprooting cardamom plants is a potential strategy for restoring tree seedling recruitment in forests with abandoned cardamom stands in the understorey, but these interventions would need to be repeated annually over many years to be successful, and they risk promoting expansion of the cover of herbaceous plants, including non-native species. Hence, this approach would be labour-intensive and costly. An alternative approach to promoting tree seedling emergence and establishment is to clear dead cardamom leaves and stems, and to encourage small-scale extraction of pods from the residual cardamom plants. Harvesting pods reduces the likelihood that the crop will be sustained in situ through natural regeneration, and supplies an income to local communities, which would enhance the social acceptability of the intervention.

Assessing the importance of human activities for the establishment of the invasivePoa annuain Antarctica

Because of its harsh environmental conditions and remoteness, Antarctica is often considered to be at low risk of plant invasion. However, an increasing number of reports have shown the presence and spread of non-native plants in Antarctica; it is therefore important to study which factors control the invasion process in this ecosystem. Here, we assessed the role of different human activities on the presence and abundance of the invasive Poa annua. In addition, we performed a reciprocal transplant experiment in the field, and a manipulative experiment of germination with P. annua and the natives Colobanthus quitensis and Deschampsia antarctica, in order to unravel the effects of physical soil disturbance on the establishment and survival of P. annua. We found a positive correlation between abundance of P. annua and level of soil disturbance, and that survival of P. annua was 33% higher in sites with disturbed soil than non-disturbed. Finally, we found that disturbance conditions increased germination for P. annua, whereas for native species germination in experimentally disturbed soil was either unchanged or reduced compared to undisturbed soil. Our results indicate that human activities that modify abiotic soil characteristics could play an important role in the abundance of this invasive species. If the current patterns of human activities are maintained in Antarctica, the establishment success and spread of P. annua could increase, negatively affecting native flora.Keywords: Alien species; Colobanthus quitensis; Deschampsia antarctica; human disturbance; Poa annua; tourists.(Published: 23 June 2014)Citation: Polar Research 2014, 33, 21425, http://dx.doi.org/10.3402/polar.v33.21425

Non-native and native shrubs have differing impacts on species diversity and composition of associated plant communities

The spread of non-native plants has been depicted as a serious threat to biodiversity. However, it remains unclear whether the indigenousness of the invading plant plays a marked role for the ecological consequences of an invasion as few studies have compared the ecological impacts of non-native shrubs with structurally or functionally comparable native shrubs. We studied patches of introduced and native shrubs to assess whether there are general differences in plant species composition or biomass between patches formed by non-native versus native shrubs. The indigenousness of the shrub (non-native vs. native) did not explain the variation in soil nutrients, neither the production of shoot biomass or allocation of growth to different parts of the shoot. The amount of light reaching ground level did not differ between patches of a non-native and a native shrub. However, species richness and biomass of herbaceous plants were lower in patches of non-native than native shrubs and the amount of litter was higher below non-native than native shrubs. Our results suggest that the indigenousness of the patch-forming plant may be an important factor for the diversity and composition of associated herbaceous vegetation. Based on our results, resource availability (light and nutrients) is not a sufficient explanation for the negative effects of non-native shrubs on plant communities. Further research is needed to investigate whether alternative explanations, such as the novelty of the toxic compounds produced by non-native plants, can explain the differences we observed.

Influence of past land use and current human disturbance on non-native plant species on small Italian islands

Biological invasions are regarded as one of the main drivers of habitat degradation in island ecosystems. Mediterranean islands have been subjected to a high degree of land conversion over the past 60 years, resulting in a massive reduction in the amount of rural land and the sprawl of tourist activities. The aims of this paper are to evaluate the current level of invasion of alien plant species in semi-natural vegetation types that have developed after the abandonment of agriculture and to analyze the relationships between non-native species, native flora, and environmental characteristics. Two Italian islands (Ponza and Ventotene) were surveyed using a random-stratified sampling. The occurrence and relative cover of alien plant species were compared and separate analyses were performed for the native flora. Abundance patterns of both native and alien species were then studied in the light of the environmental and anthropogenic features. Although we found that some non-native species are extremely widespread, their relative cover at the plot level is low. Permutational Multivariate Analysis of Variance and Indicator Species Analysis revealed dissimilarities in the native species composition, while Mann–Whitney and Kruskal–Wallis tests showed differences in the ecological requirements (moisture, soil reaction, and nitrogen) of the native species pool. Canonical Correspondence Analysis pointed to the importance of the proximity to agricultural areas, human disturbance, and past land management, particularly residual terraces, in determining the difference between plant communities on the two islands. The results of our study suggest that traditional forms of agriculture may represent a key element for countering the establishment and spread of non-native plants in Mediterranean areas.

The Role of Fire in the Establishment and Spread of Nonnative Plants in Arizona Ponderosa Pine Forests: A Review

Arizona ponderosa pine (Pinus ponderosa) forests have undergone dramatic changes since the late nineteenth century. Management practices such as fire exclusion have resulted in increased surface and tree crown fuel loads. Consequently, large and severe wildfires have been occurring more frequently in the ponderosa pine forests of Arizona. Furthermore, prescribed fire, both with and without tree thinning, is being applied to ponderosa pine forests to mitigate the risk of wildfire. Increasingly, normative plant species are spreading into burned forests regardless of fire type. In this article, we review recent literature on normative establishment in the post-fire plant community. Current research suggests an increasing risk of nonnative establishment is associated with increasing fire severity. Furthermore, wildfires seem more likely to promote nonnative species establishment than prescribed fires. The results are inconsistent, however, with some high-severity fires having few normatives and some prescribed fires strongly promoting invasion. Further research is needed to understand the mechanisms of invasion. In the 23 studies we examined, a total of 43 nonnative plant species were reported in post-fire communities. Of these, only three species were listed as noxious in Arizona: field bindweed (Convolvulus arvensis), Dalmatian toadflax (Linaria dalmatica), and Scotch cottonthistle (Onopordum acantium). Cheatgrass (Bromus tectorum), Kentucky bluegrass (Poa pratensis), and common mullein (Verbascum thapsus) were the most commonly observed species in burned areas, regardless of natural or anthropogenic ignition. Generally, nonnative presence increased after fire, but abundance of these species remained low (< 10% cover). Changes in nonnative populations reported in Arizona are consistent with those seen in ponderosa pine forests of other regions, with normatives tending to increase with increasing fire severity.

Backcountry Huts as Introduction Points for Invasion by Non-native Species into Subalpine Vegetation

The role of backcountry huts as introduction points for the establishment and spread of non-native plants into remote natural areas has received little attention. We surveyed soil and vegetation around 25 backcountry huts in the subalpine landscape of the Australian Alps to examine the role that such huts play in acting as foci for invasion by non-native species into remote mountain areas. We found that the hut surroundings were characterized by greater soil compaction, lower vegetation height, and more bare ground relative to the native plant community located 100 m from huts. At the landscape-scale, a total of 32 non-native species were recorded within 100 m of huts. Seven species were found at greater than 50% of huts (Hypochoeris radicata, Taraxacum officinale, Acetosella vulgaris, Trifolium repens, Cerastium glomeratum, Agrostis capillaris, Poa annua), and these tended to be the species that have (a) been long-established (>50–100 yrs) and (b) are the most frequent in the broader landscape. Hence, huts act to promote these ruderals by providing opportunities for their establishment, but such opportunities are not confined to hut surroundings. Several other non-native species, however, were common around huts but largely absent from the wider landscape (e.g. Anthoxanthum odoratum, Plantago major, Polygonum aviculare, Stellaria media). This suggests that some species are advantaged by the disturbance and dispersal opportunities provided by hut recreational activities in a way that is not catered for elsewhere in the Australian Alps. A weak negative relationship between non-native species richness and increasing altitude was found, but native species richness and distance of hut from access road were poor predictors of non-native species richness. Our study highlights that recreational activities may provide opportunities for the establishment of non-native plant species in remote high mountain areas, some of which are novel to the landscape, and that these may form the basis for further invasion into adjoining native vegetation.

Protected Area Safeguard Tree and Shrub Communities from Degradation and Invasion: A Case Study in Eastern Madagascar

Despite their prevalence in both developed and developing countries, there have been surprisingly few field assessments of the ecological effectiveness of protected areas. This study aimed to assess the effectiveness of a key protected area in eastern Madagascar, Ranomafana National Park (RNP). We established paired 100 x 4-m vegetation transects (400 m(2)) within RNP and in remnant forests in the park's peripheral zone. In each 400-m(2) plot, all woody stems >1.5 cm in diameter at breast height were measured and identified to species. All species were also identified as native or non-native. We identified utilitarian species within all transects and they were sorted into use category. We calculated plot-level taxonomic biodiversity and functional diversity of utilitarian species; the latter was calculated by clustering the multivariate distances between species based on their utilitarian traits, and all metrics were tested using paired t-tests. Our results showed that there was significantly higher biodiversity inside RNP than in remnant forests and this pattern was consistent across all diversity metrics examined. Forests not located within the park's boundary had significantly higher non-native species than within RNP. There was no statistically significant difference in functional diversity of utilitarian species inside RNP vs. remnant forests; however, the overall trend was toward higher diversity inside park boundaries. These findings suggested that RNP has been effective at maintaining taxonomic diversity relative to surrounding unprotected areas and restricting the spread of non-native plants. The results also suggested that low functional redundancy of forests outside of RNP might be of concern, because residents in surrounding villages may have few other substitutes for the services provided by species that are of critical importance to their livelihoods. This study highlights the challenges of trying to reconcile biodiversity conservation with human use of natural resources in economically poor, remote areas.

FLOOD REGIME AND LEAF FALL DETERMINE SOIL INORGANIC NITROGEN DYNAMICS IN SEMIARID RIPARIAN FORESTS

Flow regulation has reduced the exchange of water, energy, and materials between rivers and floodplains, caused declines in native plant populations, and advanced the spread of nonnative plants. Naturalized flow regimes are regarded as a means to restore degraded riparian areas. We examined the effects of flood regime (short [SIFI] vs. long [LIFI] inter-flood interval) on plant community and soil inorganic nitrogen (N) dynamics in riparian forests dominated by native Populus deltoides var. wislizenii Eckenwalder (Rio Grande cottonwood) and nonnative Tamarix chinensis Lour. (salt cedar) along the regulated middle Rio Grande of New Mexico. The frequency of inundation (every 2-3 years) at SIFI sites better reflected inundation patterns prior to the closure of an upstream dam relative to the frequency of inundation at LIFI sites (> or =10 years). Riparian inundation at SIFI sites varied from 7 to 45 days during the study period (April 2001-July 2004). SIFI vs. LIFI sites had higher soil moisture but greater groundwater table elevation fluctuation in response to flooding and drought. Rates of net N mineralization were consistently higher at LIFI vs. SIFI sites, and soil inorganic N concentrations were greatest at sites with elevated leaf-litter production. Sites with stable depth to ground water (approximately 1.5 m) supported the greatest leaf-litter production. Reduced leaf production at P. deltoides SIFI sites was attributed to drought-induced recession of ground water and prolonged inundation. We recommend that natural resource managers and restoration practitioners (1) utilize naturalized flows that help maintain riparian groundwater elevations between 1 and 3 m in reaches with mature P. deltoides or where P. deltoides revegetation is desired, (2) identify areas that naturally undergo long periods of inundation and consider restoring these areas to seasonal wetlands, and (3) use native xeric-adapted riparian plants to revegetate LIFI and SIFI sites where groundwater elevations commonly drop below 3 m.

Problems and Challenges of Invasive Ornamental Plants and Molecular Tools to Control Their Spread

Invasive plants, one of the most devastating ecological problems in the 21st century, cause an estimated $35 billion loss per year to the economy in the United States alone. More than 50% of all invasive plant species and 85% of invasive woody plant species were introduced originally for ornamental and landscape use. Because many non-native ornamentals are commercially important and widely utilized for various purposes, completely banning their use and prohibiting their import are unpractical solutions. On the other hand, currently used methods to control the spread of non-native plants are ineffective, expensive, or environmentally problematic. Recent advances in plant molecular biology and plant genetic transformation may enable us to create sterile cultivars of these non-native ornamental crops of high commercial value. The use of sterile cultivars should reduce or eliminate the undesirable spread of some non-native invasive plants into natural areas.

Invasiveness, invasibility and the role of environmental stress in the spread of non-native plants

Invasion ecology, the study of how organisms spread in habitats to which they are not native, asks both about the invasiveness of species and the invasibility of habitats: Which species are most likely to become invasive? Which habitats are most susceptible to invasion? To set the stage for considering these questions with regard to plants, we offer a two-way classification of nativeness and invasiveness that distinguishes natives, non-invasive non-natives and invasive non-natives. We then consider the current state of knowledge about invasiveness and invasibility. Despite much investigation, it has proven difficult to identify traits that consistently predict invasiveness. This may be largely because different traits favour invasiveness in different habitats. It has proven easier to identify types of habitats that are relatively invasible, such as islands and riverbanks. Factors thought to render habitats invasible include low intensities of competition, altered disturbance regimes and low levels of environmental stress, especially high resource availability. These factors probably often interact; the combination of altered disturbance with high resource availability may particularly promote invasibility. When biotic factors control invasibility, non-natives that are unlike native species may prove more invasive; the converse may also be true. We end with a simple conceptual model for cases in which high levels of environmental stress should and should not reduce invasibility. In some cases, it may be possible to manipulate stress to control biological invasions by plants.