Shade provided by riparian plants and biotic resistance by macrophytes reduce the establishment of an invasive Poaceae (original) (raw)
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Native macrophyte density and richness affect the invasiveness of a tropical Poaceae species
PLoS ONE 8(3): e60004. doi:10.1371/journal.pone.0060004
The role of the native species richness and density in ecosystem invasibility is a matter of concern for both ecologists and managers. We tested the hypothesis that the invasiveness of Urochloa arrecta (non-native in the Neotropics) is negatively affected by the species richness and abundance of native aquatic macrophytes in freshwater ecosystems. We first created four levels of macrophyte richness in a greenhouse (richness experiment), and we then manipulated the densities of the same native species in a second experiment (density experiment). When the native macrophytes were adults, fragments of U. arrecta were added, and their growth was assessed. Our results from the richness experiment corroborated the hypothesis of a negative relationship between the native species richness and the growth of U. arrecta, as measured by sprout length and root biomass. However, the resistance to invasion was not attributed to the presence of a particular native species with a greater competitive ability. In the density experiment, U. arrecta growth decreased significantly with an increased density of all five of the native species. Density strongly affected the performance of the Poaceae in a negative manner, suggesting that patches that are densely colonized by native macrophytes and less subject to disturbances will be more resistant to invasion than those that are poorly colonized and more commonly subjected to disturbances. Our density experiment also showed that some species exhibit a higher competitive ability than others (sampling effect). Although native richness and abundance clearly limit the colonization and establishment of U. arrecta, these factors cannot completely prevent the invasion of aquatic ecosystems by this Poaceae species.
Spatial patterns of plant invasiveness in a riparian corridor
Landscape Ecology, 2005
Analysis of landscape-scale patterns of plant invasiveness can assist in interpreting spatial patterns of plant species richness. We investigated downstream variation in plant invasiveness in the riparian corridor of the free-flowing Vindel River in northern Sweden by introducing seeds of an alien species, Helianthus annuus, in 0.25 m 2 plots of natural vegetation from mountain headwaters to the coast and found a significant downstream pattern with middle reaches having the highest invasiveness. We related invasiveness to species richness, both on a reach scale (200-m long stretches of riverbank encompassing the experimental plots) and on the scale of experimental plots. We found no significant correlation between plant invasiveness and species richness, neither at the reach nor at the plot scale. The number of available soil substrates shows a significant positive quadratic relationship with location along the river and substrate fineness shows a near significant negative quadratic relationship with location along the river, with middle reaches having coarser substrates. Several studies have shown that plant species richness in riparian corridors often exhibits a quadratic pattern with highest species richness in the middle reaches of a river, similar to the pattern we found for invasiveness. Although species richness per se might not be a primary factor for invasibility, the same habitat conditions as those supporting plant species richness, can help in explaining large-scale patterns of plant invasion in riparian zones.
Aquatic Sciences, 2012
Biotic and abiotic factors are filters that prevent invasions in aquatic and terrestrial ecosystems. In this investigation we tested the hypothesis that the success of a non-native Poaceae (Urochloa subquadripara) is positively correlated with the richness of native macrophytes and negatively correlated with wind disturbance (fetch) and presence of riparian vegetation on coarse spatial scales. Our samplings were carried out in a tropical reservoir (Rosana Reservoir, Brazil). We first compared competing models using the Akaike criterion to find the main combinations of explanatory variables (native macrophyte richness, fetch, and presence of riparian vegetation) associated with the success of U. subquadripara. Then, we applied multiple regressions to assess the coefficient of determination of the best models selected according to the Akaike criterion. The probability of occurrence of U. subquadripara increased significantly with increases in the number of native macrophyte species, but decreased with fetch and the presence of riparian vegetation. Stand width and maximum depth of occurrence (indicators of the success of this Poaceae) were also positively related with native richness and negatively with fetch and riparian vegetation. Our results supported our expectation that wave disturbance is an important variable explaining U. subquadripara success. Because the less exposed sites are also more favorable for colonization by natives, positive relationships between the success of non-native species and native diversity emerge at the coarse scale. Taken together, our results support the theory of ''biotic acceptance''; that is, favorable sites are more prone to colonization by both native and non-native species.
River Research and Applications, 2012
Management methods to control or eradicate invasive alien species should be guided by research into their efficacy in relation to the target species as well as their wider effects on the community. Impatiens glandulifera Royle (Balsaminaceae) is an invasive alien species, which has spread rapidly across Europe and North America, particularly colonizing riverbanks, wet woodlands, and wastelands. The effectiveness of two mechanical control measures and their impacts on community plant species richness and diversity within the riparian zone of the urban river Brent, London, England, was assessed. Over 2 years, an experiment was performed across three sites that exhibited contrasting levels of invasion of I. glandulifera: high, moderate and low. The experiment involved three treatments on replicated plots at all three sites: pruning at 6-week intervals, weeding at 6-week intervals, and a control. The effects of these control measures were most clearly seen at the site with the highest level of invasion and, to a smaller extent, at the moderately invaded site. Weeding was more successful in controlling the species than pruning, and the greatest impact of these treatments on community plant species richness and diversity was only apparent after 2 years of the experiment. Although seedlings of 10 other alien species were found, there was no evidence that their presence on the plots was detrimental to native species during the experimental period. Three common native species each approached 10% cover on the weeded plots at the heavily invaded site by the end of the experiment: Poa annua, Rumex obtusifolius, and Urtica dioica. These assessments provide guidance for implementing mechanical control of I. glandulifera in riparian zones.
Urban Ecosystems, 2018
Invasive species have been causing important and irreversible impacts to native species and communities of ecosystems. They distort ecosystem functions by degrading forest lands, wetlands, and agricultural habitats and replace the native vegetation and reduce biodiversity, forest productivity, and suitable wildlife habitat. To address disturbances caused by invasive species occurrence, further information is needed regarding the occurrence, extent, and dispersal of invasive species and how land use may increase the spread of these species. The objective of this study was to find the frequency and dominance of three invasive species common to riparian areas of east Alabama: Ligustrum sinense (Chinese privet), Elaeagnus pungens (silverthorn), and Triadica sebifera (Chinese tallow tree). Surveys of these species in riparian forests in and around Auburn, Alabama were conducted to show the relative extent of these shrubs and their relation to urban land use. It was expected to see the highest levels of invasive species in the city center with decreasing levels radiating outward into rural areas. Another objective was how urban land use may affect the presence-absence and prevalence of these non-native plant species within study sites. The results showed that around the city center and suburban lands, cover of both Chinese privet and silverthorn tended to increase. In contrast, Chinese tallow tree density percent cover showed an opposite trend with landscapes close to city center often having slightly less cover. This study shows that urban land use may be an important association with distribution of invasive plant species.
Do Aquatic Macrophytes Limit the Invasion Potential of Exotic Species in Pantanal Grasslands?
Wetlands, 2019
Natural disturbances have the potential to limit exotic species invasions. The exotic grass, Urochloa humidicola, has high propagation potential following seasonal flooding, but, flooding tends to reduce the cover. Neither the potential for U. humidicola form a seed bank for recruitment following seasonal flooding, nor the mechanism responsible for reducing adult plant cover during floods is currently known. The soil seed bank of a U. humidicola was sampled for 2 years. To examine the potential role of competition with aquatic macrophytes in reducing its cover during floods, cuttings of U. humidicola were flooded in tanks in presence and absence of aquatic macrophytes for 3 months. Seedling density of U. humidicola was higher post-flood (245 seedlings/m −2) than the post-dry (130 seedlings/m −2). Germination occurred throughout the year, with highest seedling densities at the five to 7 months following soil collection. Competition with aquatic plants significantly increased mortality (c. 70%) of inundated U. humidicola. Our findings suggest that the survival potential of U. humidicola under flood is high, but is limited by shading of aquatic macrophytes. Nonetheless, its seed bank germinates throughout the year, though delayed by flooding. Control of invasive species in grasslands of the Pantanal depend on natural hydrological and biological drives.