Moussab/ORKG-training-evaluation-set huggingface dataset:
Research field: Ecology and Evolutionary Biology
Title: Alien Grass Invasion and Fire In the Seasonal Submontane Zone of Hawaii
Abstract: Island ecosystems are notably susceptible to biological invasions (Elton 1958), and the Hawaiian islands in particular have been colonized by many introduced species (Loope and Mueller-Dombois 1989). Introduced plants now dominate extensive areas of the Hawaiian Islands, and 86 species of alien plants are presently considered to pose serious threats to Hawaiian communities and ecosystems (Smith 1985). Among the most important invasive plants are several species of tropical and subtropical grasses that use the C4 photosynthetic pathway. These grasses now dominate extensive areas of dry and seasonally dry habitats in Hawai'i. They may compete with native species, and they have also been shown to alter hydrological properties in the areas they invade (MuellerDombois 1973). Most importantly, alien grasses can introduce fire into areas where it was previously rare or absent (Smith 1985), thereby altering the structure and functioning of previously native-dominated ecosystems. Many of these grasses evolved in fire-affected areas and have mechanisms for surviving and recovering rapidly from fire (Vogl 1975, Christensen 1985), while most native species in Hawai'i have little background with fire (Mueller-Dombois 1981) and hence few or no such mechanisms. Consequently, grass invasion could initiate a grass/fire cycle whereby invading grasses promote fire, which in turn favors alien grasses over native species. Such a scenario has been suggested in a number of areas, including Latin America, western North America, Australia, and Hawai'i (Parsons 1972, Smith 1985, Christensen and Burrows 1986, Mack 1986, MacDonald and Frame 1988). In most of these cases, land clearing by humans initiates colonization by alien grasses, and the grass/fire cycle then leads to their persistence. In Hawai'i and perhaps other areas, however, grass invasion occurs without any direct human intervention. Where such invasions initiate a grass/fire cy-
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Human activity facilitates altitudinal expansion of exotic plants along a road in montane grassland, South Africa
Abstract: ABSTRACT Question: Do anthropogenic activities facilitate the distribution of exotic plants along steep altitudinal gradients? Location: Sani Pass road, Grassland biome, South Africa. Methods: On both sides of this road, presence and abundance of exotic plants was recorded in four 25-m long road-verge plots and in parallel 25 m × 2 m adjacent land plots, nested at five altitudinal levels: 1500, 1800, 2100, 2400 and 2700 m a.s.l. Exotic community structure was analyzed using Canonical Correspondence Analysis while a two-level nested Generalized Linear Model was fitted for richness and cover of exotics. We tested the upper altitudinal limits for all exotics along this road for spatial clustering around four potential propagule sources using a t-test. Results: Community structure, richness and abundance of exotics were negatively correlated with altitude. Greatest invasion by exotics was recorded for adjacent land at the 1500 m level. Of the 45 exotics, 16 were found at higher altitudes than expected and observations were spatially clustered around potential propagule sources. Conclusions: Spatial clustering of upper altitudinal limits around human inhabited areas suggests that exotics originate from these areas, while exceeding expected altitudinal limits suggests that distribution ranges of exotics are presently underestimated. Exotics are generally characterised by a high propagule pressure and/or persistent seedbanks, thus future tarring of the Sani Pass may result in an increase of exotic species richness and abundance. This would initially result from construction-related soil disturbance and subsequently from increased traffic, water run-off, and altered fire frequency. We suggest examples of management actions to prevent this. Nomenclature: Germishuizen & Meyer (2003).
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Alien plant dynamics following fire in Mediterranean-climate California shrublands
Abstract: Over 75 species of alien plants were recorded during the first five years after fire in southern California shrublands, most of which were European annuals. Both cover and richness of aliens varied between years and plant association. Alien cover was lowest in the first postfire year in all plant associations and remained low during succession in chaparral but increased in sage scrub. Alien cover and richness were significantly correlated with year (time since disturbance) and with precipitation in both coastal and interior sage scrub associations. Hypothesized factors determining alien dominance were tested with structural equation modeling. Models that included nitrogen deposition and distance from the coast were not significant, but with those variables removed we obtained a significant model that gave an R 2 5 0.60 for the response variable of fifth year alien dominance. Factors directly affecting alien dominance were (1) woody canopy closure and (2) alien seed banks. Significant indirect effects were (3) fire intensity, (4) fire history, (5) prefire stand structure, (6) aridity, and (7) community type. According to this model the most critical factor in- fluencing aliens is the rapid return of the shrub and subshrub canopy. Thus, in these communities a single functional type (woody plants) appears to the most critical element controlling alien invasion and persistence. Fire history is an important indirect factor be- cause it affects both prefire stand structure and postfire alien seed banks. Despite being fire-prone ecosystems, these shrublands are not adapted to fire per se, but rather to a particular fire regime. Alterations in the fire regime produce a very different selective environment, and high fire frequency changes the selective regime to favor aliens. This study does not support the widely held belief that prescription burning is a viable man- agement practice for controlling alien species on semiarid landscapes.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Are invasive species the drivers or passengers of change in degraded ecosystems?
Abstract: Few invaded ecosystems are free from habitat loss and disturbance, leading to uncertainty whether dominant invasive species are driving community change or are passengers along for the environmental ride. The ''driver'' model predicts that invaded communities are highly interactive, with subordinate native species being limited or ex- cluded by competition from the exotic dominants. The ''passenger'' model predicts that invaded communities are primarily structured by noninteractive factors (environmental change, dispersal limitation) that are less constraining on the exotics, which thus dominate. We tested these alternative hypotheses in an invaded, fragmented, and fire-suppressed oak savanna. We examined the impact of two invasive dominant perennial grasses on community structure using a reduction (mowing of aboveground biomass) and removal (weeding of above- and belowground biomass) experiment conducted at different seasons and soil depths. We examined the relative importance of competition vs. dispersal limitation with experimental seed additions. Competition by the dominants limits the abundance and re- production of many native and exotic species based on their increased performance with removals and mowing. The treatments resulted in increased light availability and bare soil; soil moisture and N were unaffected. Although competition was limiting for some, 36 of 79 species did not respond to the treatments or declined in the absence of grass cover. Seed additions revealed that some subordinates are dispersal limited; competition alone was insufficient to explain their rarity even though it does exacerbate dispersal inefficiencies by lowering reproduction. While the net effects of the dominants were negative, their presence restricted woody plants, facilitated seedling survival with moderate disturbance (i.e., treatments applied in the fall), or was not the primary limiting factor for the occurrence of some species. Finally, the species most functionally distinct from the dominants (forbs, woody plants) responded most significantly to the treatments. This suggests that relative abundance is determined more by trade-offs relating to environmental conditions (long- term fire suppression) than to traits relating to resource capture (which should most impact functionally similar species). This points toward the passenger model as the underlying cause of exotic dominance, although their combined effects (suppressive and facilitative) on community structure are substantial.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Predicting Richness of Native, Rare, and Exotic Plants in Response to Habitat and Disturbance Variables across a Variegated Landscape
Abstract: Species richness of native, rare native, and exotic understorey plants was recorded at 120 sites in temperate grassy vegetation in New South Wales. Linear models were used to predict the effects of environment and disturbance on the richness of each of these groups. Total native species and rare native species showed similar responses, with rich- ness declining on sites of increasing natural fertility of par- ent material as well as declining under conditions of water
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Disturbance-mediated competition and the spread of Phragmites australis in a coastal marsh
Abstract: In recent decades the grass Phragmites australis has been aggressively in- vading coastal, tidal marshes of North America, and in many areas it is now considered a nuisance species. While P. australis has historically been restricted to the relatively benign upper border of brackish and salt marshes, it has been expanding seaward into more phys- iologically stressful regions. Here we test a leading hypothesis that the spread of P. australis is due to anthropogenic modification of coastal marshes. We did a field experiment along natural borders between stands of P. australis and the other dominant grasses and rushes (i.e., matrix vegetation) in a brackish marsh in Rhode Island, USA. We applied a pulse disturbance in one year by removing or not removing neighboring matrix vegetation and adding three levels of nutrients (specifically nitrogen) in a factorial design, and then we monitored the aboveground performance of P. australis and the matrix vegetation. Both disturbances increased the density, height, and biomass of shoots of P. australis, and the effects of fertilization were more pronounced where matrix vegetation was removed. Clear- ing competing matrix vegetation also increased the distance that shoots expanded and their reproductive output, both indicators of the potential for P. australis to spread within and among local marshes. In contrast, the biomass of the matrix vegetation decreased with increasing severity of disturbance. Disturbance increased the total aboveground production of plants in the marsh as matrix vegetation was displaced by P. australis. A greenhouse experiment showed that, with increasing nutrient levels, P. australis allocates proportionally more of its biomass to aboveground structures used for spread than to belowground struc- tures used for nutrient acquisition. Therefore, disturbances that enrich nutrients or remove competitors promote the spread of P. australis by reducing belowground competition for nutrients between P. australis and the matrix vegetation, thus allowing P. australis, the largest plant in the marsh, to expand and displace the matrix vegetation. Reducing nutrient load and maintaining buffers of matrix vegetation along the terrestrial-marsh ecotone will, therefore, be important methods of control for this nuisance species.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Herbaceous layer contrast and alien plant occurrence in utility corridors and riparian forests of the Allegheny High Plateau
Abstract: communities by alien plant species that can adversely affect community structure and function. To determine how corridor establishment influences riparian vegetation of the Allegheny High Plateau of northwestern Pennsylvania, we compared the species composition and richness of the herbaceous layer (all vascular plants s 1 m tall) of utility corridors and adjacent headwater riparian forests, and tested the hypothesis that utility corridors serve as foci for the invasion of adjacent riparian forest by alien vascular plants. We contrasted plant species richness and vegetative cover, cover by growth form, species richness and cover of alien plants and cover of microhabitat components (open soil, rock, leaf litter, log, bryophyte) in utility corridors and adjacent riparian forest at 17 sites. Cluster analysis revealed that herbaceous layer species assemblages in corridors and riparian forest were compositionally distinct. Herbaceous layer cover and species richness were significantly (P s 0.05) greater in corridors than in riparian forest. Fern, graminoid, and forb species co-dominated herbaceous layer cover in corridors; fern cover dominated riparian forests. Cover of alien plants was significantly greater in corridors than in riparian forest. Alien plant species richness and cover were significantly and positively correlated with open soil, floodplain width, and active channel width in corridors but were significantly and negatively correlated with litter cover in riparian forest. Given that the majority of alien plant species we found in corridors were shade-intolerant and absent from riparian forests, we conclude that open utility corridors primarily serve as habitat refugia, rather than as invasion foci, for alien plant species in riparian forests of the Allegheny High Plateau.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Feral sheep on Socorro Island: facilitators of alien plant colonization and ecosystem decay
Abstract: The paper examines the role of feral sheep (Ovis aries) in facilitating the naturalization of alien plants and degrading a formerly robust and stable ecosystem of Socorro, an isolated oceanic island in the Mexican Pacific Ocean. Approximately half of the island is still sheep‐free. The other half has been widely overgrazed and transformed into savannah and prairie‐like open habitats that exhibit sheet and gully erosion and are covered by a mix of native and alien invasive vegetation today. Vegetation transects in this moderately sheep‐impacted sector show that a significant number of native and endemic herb and shrub species exhibit sympatric distribution patterns with introduced plants. Only one alien plant species has been recorded from any undisturbed and sheep‐free island sector so far.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: The vulnerability of habitats to plant invasion: disentangling the roles of propagule pressure, time and sampling effort
Abstract: Aim To quantify the vulnerability of habitats to invasion by alien plants having accounted for the effects of propagule pressure, time and sampling effort. Location New Zealand. Methods We used spatial, temporal and habitat information taken from 9297 herbarium records of 301 alien plant species to examine the vulnerability of 11 terrestrial habitats to plant invasions. A null model that randomized species records across habitats was used to account for variation in sampling effort and to derive a relative measure of invasion based either on all records for a species or only its first record. The relative level of invasion was related to the average distance of each habitat from the nearest conurbation, which was used as a proxy for propagule pressure. The habitat in which a species was first recorded was compared to the habitats encountered for all records of that species to determine whether the initial habitat could predict subsequent habitat occupancy. Results Variation in sampling effort in space and time significantly masked the underlying vulnerability of habitats to plant invasions. Distance from the nearest conurbation had little effect on the relative level of invasion in each habitat, but the number of first records of each species significantly declined with increasing distance. While Urban, Streamside and Coastal habitats were over-represented as sites of initial invasion, there was no evidence of major invasion hotspots from which alien plants might subsequently spread. Rather, the data suggest that certain habitats (especially Roadsides) readily accumulate alien plants from other habitats. Main conclusions Herbarium records combined with a suitable null model provide a powerful tool for assessing the relative vulnerability of habitats to plant invasion. The first records of alien plants tend to be found near conurbations, but this pattern disappears with subsequent spread. Regardless of the habitat where a species was first recorded, ultimately most alien plants spread to Roadside and Sparse habitats. This information suggests that such habitats may be useful targets for weed surveillance and monitoring.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Factors explaining alien plant invasion success in a tropical ecosystem differ at each stage of invasion
Abstract: 1 Understanding why some alien plant species become invasive when others fail is a fundamental goal in invasion ecology. We used detailed historical planting records of alien plant species introduced to Amani Botanical Garden, Tanzania and contemporary surveys of their invasion status to assess the relative ability of phylogeny, propagule pressure, residence time, plant traits and other factors to explain the success of alien plant species at different stages of the invasion process. 2 Species with native ranges centred in the tropics and with larger seeds were more likely to regenerate, whereas naturalization success was explained by longer residence time, faster growth rate, fewer seeds per fruit, smaller seed mass and shade tolerance. 3 Naturalized species spreading greater distances from original plantings tended to have more seeds per fruit, whereas species dispersed by canopy‐feeding animals and with native ranges centred on the tropics tended to have spread more widely in the botanical garden. Species dispersed by canopy‐feeding animals and with greater seed mass were more likely to be established in closed forest. 4 Phylogeny alone made a relatively minor contribution to the explanatory power of statistical models, but a greater proportion of variation in spread within the botanical garden and in forest establishment was explained by phylogeny alone than for other models. Phylogeny jointly with variables also explained a greater proportion of variation in forest establishment than in other models. Phylogenetic correction weakened the importance of dispersal syndrome in explaining compartmental spread, seed mass in the forest establishment model, and all factors except for growth rate and residence time in the naturalization model. 5 Synthesis. This study demonstrates that it matters considerably how invasive species are defined when trying to understand the relative ability of multiple variables to explain invasion success. By disentangling different invasion stages and using relatively objective criteria to assess species status, this study highlights that relatively simple models can help to explain why some alien plants are able to naturalize, spread and even establish in closed tropical forests.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: The role of propagule pressure, genetic diversity and microsite availability for Senecio vernalis invasion
Abstract: Genetic diversity is supposed to support the colonization success of expanding species, in particular in situations where microsite availability is constrained. Addressing the role of genetic diversity in plant invasion experimentally requires its manipulation independent of propagule pressure. To assess the relative importance of these components for the invasion of Senecio vernalis, we created propagule mixtures of four levels of genotype diversity by combining seeds across remote populations, across proximate populations, within single populations and within seed families. In a first container experiment with constant Festuca rupicola density as matrix, genotype diversity was crossed with three levels of seed density. In a second experiment, we tested for effects of establishment limitation and genotype diversity by manipulating Festuca densities. Increasing genetic diversity had no effects on abundance and biomass of S. vernalis but positively affected the proportion of large individuals to small individuals. Mixtures composed from proximate populations had a significantly higher proportion of large individuals than mixtures composed from within seed families only. High propagule pressure increased emergence and establishment of S. vernalis but had no effect on individual growth performance. Establishment was favoured in containers with Festuca, but performance of surviving seedlings was higher in open soil treatments. For S. vernalis invasion, we found a shift in driving factors from density dependence to effects of genetic diversity across life stages. While initial abundance was mostly linked to the amount of seed input, genetic diversity, in contrast, affected later stages of colonization probably via sampling effects and seemed to contribute to filtering the genotypes that finally grew up. In consequence, when disentangling the mechanistic relationships of genetic diversity, seed density and microsite limitation in colonization of invasive plants, a clear differentiation between initial emergence and subsequent survival to juvenile and adult stages is required.
Extracted statement — Investigated species: Plants