Abundance Of Invasive Plants Research Articles

Negative per capita effects of purple loosestrife and reed canary grass on plant diversity of wetland communities

ABSTRACTInvasive plants can simplify plant community structure, alter ecosystem processes and undermine the ecosystem services that we derive from biotic diversity. Two invasive plants, purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinacea), are becoming the dominant species in many wetlands across temperate North America. We used a horizontal, observational study to estimate per capita effects (PCEs) of purple loosestrife and reed canary grass on plant diversity in 24 wetland communities in the Pacific Northwest, USA. Four measures of diversity were used: the number of species (S), evenness of relative abundance (J), the Shannon–Wiener index (H′) and Simpson's index (D). We show that (1) the PCEs on biotic diversity were similar for both invasive species among the four measures of diversity we examined; (2) the relationship between plant diversity and invasive plant abundance ranges from linear (constant slope) to negative exponential (variable slope), the latter signifying that the PCEs are density‐dependent; (3) the PCEs were density‐dependent for measures of diversity sensitive to the number of species (S, H′, D) but not for the measure that relied solely upon relative abundance (J); and (4) invader abundance was not correlated with other potential influences on biodiversity (hydrology, soils, topography). These results indicate that both species are capable of reducing plant community diversity, and management strategies need to consider the simultaneous control of multiple species if the goal is to maintain diverse plant communities.

Controls over invasion of Bromus tectorum: The importance of climate, soil, disturbance and seed availability

AbstractQuestion: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi‐arid ecosystems where water is a limiting resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool‐season annual grass that has successfully colonized much of the U.S. Great Basin?Location: Short‐grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern Washington, USA; and the Patagonian steppe of the Chubut province in Argentina.Methods: We utilized a soil water model to simulate seasonal soil water dynamics in multiple combinations of climatic and soil properties. In addition, we utilized a gap dynamics model to simulate the impact of disturbance regime and seed availability on competition between B. tectorum and native plants.Results: Our results suggest that climate is very important, but that soil properties do not significantly influence the probability of observing conditions suitable for B. tectorum establishment. Results of the plant competition model indicate that frequent disturbance causes more Bromus tectorum in invaded areas and higher seed availability causes faster invasion.Conclusions: These results imply a general framework for understanding Bromus tectorum invasion in which climatic conditions dictate which areas are susceptible to invasion, disturbance regime dictates the severity of invasion and seed availability dictates the speed of invasion.

Controls over invasion of Bromus tectorum: The importance of climate, soil, disturbance and seed availability

Question: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi-arid ecosystems where water is a limiting resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool-season annual grass that has successfully colonized much of the U.S. Great Basin? Location: Short-grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern Washington, USA; and the Patagonian steppe of the Chubut province in Argentina. Methods: We utilized a soil water model to simulate seasonal soil water dynamics in multiple combinations of climatic and soil properties. In addition, we utilized a gap dynamics model to simulate the impact of disturbance regime and seed availability on competition between B. tectorum and native plants. Results: Our results suggest that climate is very important, but that soil properties do not significantly influence the probability of observing conditions suitable for B. tectorum establishment. Results of the plant competition model indicate that frequent disturbance causes more Bromus tectorum in invaded areas and higher seed availability causes faster invasion. Conclusions: These results imply a general framework for understanding Bromus tectorum invasion in which climatic conditions dictate which areas are susceptible to invasion, disturbance regime dictates the severity of invasion and seed availability dictates the speed of invasion.

Invertebrate predation on the water lily beetle, Galerucella nymphaeae (Coleoptera: Chrysomelidae), and its implications for potential biological control of water chestnut, Trapa natans

Abstract Classical biological weed control attempts to reduce abundance of invasive plants through introduction of specialized herbivores. Biocontrol programs emphasize introduction of organisms free of parasitoids and diseases from their native range. Unfortunately, a significant number of programs fail due to interference by resident natural enemies. Ecologically similar native herbivores in release areas offer an opportunity to assess presence and magnitude of biotic interference. We evaluated whether water strider Gerris insperatus , ladybird beetle Coleomegilla maculata , and backswimmer Notonecta spp., are important predators of a native leaf beetle, Galerucella nymphaeae which feeds on both the native water lily Nuphar lutea and introduced water chestnut, Trapa natans . Galerucella numphaeae is morphologically and ecologically similar to Galerucella birmanica , an Asian leaf beetle being investigated as potential biocontrol agent of T. natans . Notonecta always rejected G. nymphaeae larvae while G. insperatus and C. maculata predation significantly reduced larval and pupal survival. Identity of G. nymphaeae larval host plant ( T. natans or native N. lutea ) did not affect experimental outcomes, demonstrating that predation by G. insperatus and C. maculata could interfere with establishment and population build-up of G. birmanica . Various release methods, including cages, mass releases, habitat variables, timing of releases, and releases of different developmental stages should be evaluated for their ability to overcome potential biotic resistance from resident predators. Monitoring of associated plant, herbivore, and predator populations, including the development of food web models using stable isotopes may represent useful approaches to assess the overall ecological impact (including potential non-target effects) of a potential biocontrol agent release targeting T. natans .

Influence of Land Use and Site Characteristics on Invasive Plant Abundance in the Quinebaug Highlands of Southern New England

Abstract Invasive exotic plants have been identified as one of the major threats to ecosystem function and biodiversity. This study examined the distribution and abundance (cover and frequency) of invasive plants in natural habitats of the Quinebaug Highlands forest block (13,760 ha) of northern Connecticut and southern Massachusetts in relation to current and historical land use and site conditions. Multiple regression and GIS analyses were used to identify areas of high infestation and factors most useful in predicting invasions. Celastrus orbiculatus, Rosa multiflora, and Berberis thunbergii were the most frequent invasives. Past land use was the strongest predictor of invasive cover (r2 = 0.219) and richness (r2 = 0.303; p < 0.001 both regressions). Current land development and physical soil characteristics were also strongly correlated. These results add to our understanding of factors promoting plant invasions. Because invasive species control in natural areas is time- and resource-intensive, this i...

Positive relationships between invasive purple loosestrife (Lythrum salicaria) and plant species diversity and abundance in Minnesota wetlands

Plant species invasions may result from, and cause, changes in the vegetation community and abiotic environment. It is often hypothesized that nonnative plant invaders suppress the diversity of native species. We examined relationships of vegetation and environmental gradients associated with the nonnative invasive wetland plant Lythrum salicaria L. to determine whether L. salicaria invasion is associated with reduced diversity and abundance of resident plant species in the wetland community. Vegetation and environmental variables were surveyed in 10 wetlands defining a gradient of L. salicaria abundance. In addition, relationships among variables were compared between invaded, Lythrum-dominated and uninvaded, Typha-dominated patches within 6 of the 10 invaded wetlands. Contrary to expectations, ordination results showed that plant diversity was higher in invaded than in uninvaded patches. Lythrum salicaria replaced other plant density and biomass on a one-to-one basis. The ordination results generated an unexpected competing set of testable hypotheses regarding whether L. salicaria invades diverse plant communities or enhances plant community diversity.Key words: invasion, Lythrum salicaria, ordination, plant community composition, Typha-dominated marshes, wetlands.

Non-Indigenous Woody Invasive Plants in a Rural New England Town

We investigated the abundance of non-indigenous woody invasive plants in Farmington, Maine, a rural New England town in a forested landscape. We found 12 invasive species and more than 7 patches per km from surveys on 33 transects (54.3 km) along field edges, abandoned railroad right-of-ways, roadsides, and riparian zones. Invasive abundance was apparently lower than for more developed areas of the northeastern US, where, in contrast to western Maine, invasives have extensively penetrated forest interiors. Invasive abundance increased with the amount of landscaping and proximity to town, suggesting a close association between local horticulture and the spread of woody invasives. Invasive abundance and diversity were highest in riparian areas, probably due to relatively high levels of propagule pressure. Species differed in the extent of invasiveness, ranging from those still dependent on planted parent trees to fully invasive populations. The invasive species recorded in this study have caused environmental and economic damage elsewhere. The lower levels of invasiveness in Farmington are likely a result of the isolation, small human population, and forested landscape rather than low levels of invasibility. This suggests the potential for future risks, and the importance of intervention while populations can still be eradicated or controlled.

Are Mojave Desert annual species equal? Resource acquisition and allocation for the invasive grass Bromus madritensis subsp. rubens (Poaceae) and two native species

Abundance of invasive plants is often attributed to their ability ot outcompete native species. We compared resource acquisition and allocation of the invasive annual grass Bromus madritensis subsp. rubens with that of two native Mojave Desert annuals, Vulpia octoflora and Descurainia pinnata, in a glasshouse experiment. Each species was grown in monoculture at two densities and two levels of N availability to compare how these annuals capture resources and to understand their relative sensitivities to environmental change. During >4 mo of growth, Bromus used water more rapidly and had greater biomass and N content than the natives, partly because of its greater root-surface area and its exploitation of deep soils. Bromus also had greater N uptake, net assimilation and transpiration rates, and canopy area than Vulpia. Resource use by Bromus was less sensitive to changes in N availability or density than were the natives. The two native species in this study produced numerous small seeds that tended to remain dormant, thus ensuring escape of offspring from unfavorable germination conditions; Bromus produced fewer but larger seeds that readily germinated. Collectively, these traits give Bromus the potential to rapidly establish in diverse habitats of the Mojave Desert, thereby gaining an advantage over coexisting native species.

Invasive alien woody plants of the southern and southwestern Cape region, South Africa

The frequency and abundance of invasive alien plants were recorded along roadsides and at watercourse crossings in 82.9% (145/175) of the quarter degree squares in the study area (3I-35°S, 17-25°E and covering ± 90 000 km:). The sur­vey yielded 102 species of which the most prominent (in order of prominence) in roadside and veld (natural and modified) habitats were: Acacia cyclops, A. saligna and A. mearnsii The most prominent species (in order of prominence) in stream- bank habitats were: A. mearnsii, A. saligna and Populus x canescens.

Invasive alien woody plants of the eastern Cape

The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 69.9% (151/216) of the quarter degree squares in the study area. The survey yielded 101 species of which the most prominent (in order of prominence) in roadside and veld habitats were: Opuntia ficus-indica, Acacia meamsii and A. cyclops. The most prominent species (in order of prominence) in streambank habitats were: A. meamsii, Populus x canescens, Salix babylonica and S. fragilis (fide R.D. Meikle).The greatest intensity of invasion was recorded in the wetter eastern parts and particularly in the vicinity of Port Elizabeth. Uitenhage, East London, Grahamstown, Hogsback and Stutterheim. There was relatively little invasion in the central and western dry interior except along watercourses.

Invasive alien woody plants of the northern Cape

The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 31% (90/286) of the quarter degree squares in the study area. The survey yielded 23 species of which the most prominent invaders were Prosopis spp. The most prominent remaining species were: Opuntia ficus-indica, Nicotiana glauca and Melia azedarach. The greatest abundance and diversity of alien invader plants were recorded near human settlements. More than half of the total recorded species have invaded perennial riverbanks. The episodic Molopo and Kuruman Rivers have been invaded almost exclusively by Prosopis spp., which in places have formed extensive stands.

Invasive alien woody plants of the Orange Free State

The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 66% (151/230) of the quarter degree squares in the study area. The survey yielded 64 species of which the most prominent (in order of prominence) in streambank habitats were: Salix babylonica, Populus x canescens, Acacia dealbata and Salix fragilis (fide R.D. Meikle pers. comm ). The most prominent species (in order of prominence) in roadside and veld habitats were: Opunlia ficus-indica, Prunus persica, Eucalyptus spp.. Rosa eglanteria, Pyracantha angustifolia and Acacia dealbata.Little invasion was recorded for most of the province. The greatest intensity of invasion was recorded along the perennial rivers and rocky hillsides in the moist grassland of the eastern mountain region bordering on Lesotho and Natal.

Invasive alien woody plants of Natal and the north-eastern Orange Free State

The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 87% (152/175) of the quarter degree squares in the study area. The survey yielded BO species of which the most prominent species (in order of prominence) in roadside and veld habitats were: Chromolaena odoruta, Solatium mauritianum, Psidium guajava, Rubus spp., Acacia meamsu and Lantana camara The most prominent species (in order of prominence) in streambank habitats were: Acacia dealbata, A. meamsii and Salix babylonica.The greatest intensity of invasion was recorded in the Natal midlands and in the coastal belt of southern Natal, including the metropolitan areas of Pietermaritzburg and Durban. There was relatively little invasion in the north-eastern lowlands of Natal but the potential for expansion is great. Little invasion was recorded in the north-eastern Orange Free State except along some watercourses.