A field experiment from 2003 to 2005 at two sites examined the impacts of forage species and legume proportion on forage sward production. Grasses generally established rapidly and out-yielded swards high in legume content, although legumes did improve forage quality. Alfalfa was retained at greater relative biomass in mixed swards than swards containing clover. Legume persistence also varied depending on neighbouring grass species. A greenhouse study examined competitive interactions between Canada thistle (a common pasture weed), white clover and Kentucky bluegrass during establishment. Although thistle was most susceptible to intra-specific competition, and strongly affected forage yield, the latter also influenced weed biomass. Competitiveness of forages depended directly on soil medium, emphasizing the importance of abiotic factors on vegetation dynamics in mixed swards. / Rangeland and Wildlife Resources

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The aim of this diploma thesis "The determination of the production of seeds and their germination for selected species from the weedy family Asteraceae" is to find out the production of seeds and their germination of two selected weedy species from the family Asteraceae, depending on the location. The following were selected: Creeping Thistle (Cirsium arvense) and Wormwood (Artemisia vulgaris). Seed collection was done at seven locations with different habitat conditions (unmaintained hayfield, recultivated rubbish, garden, grass vegetation with grazing breeding of cattle, permanent grass vegetation, grasslands on arable land, forest land, other road, other area). After reviewing the available literature is discussed the biology and control of weeds and their significance. Furthermore is also characterized the family Asteraceae and selected representatives of this family . Subsequently is characterized the territory of interest. In addition is discussed the problematics of germination and seed production for Creeping Thistle (Cirsium arvense) and Wormwood (Artemisia vulgaris) depending on their habitats. The overall average HTS of Wormwood was 0.08 g, the average germination was 79%. The total average seed production of Creeping Thistle was 1 299 seeds, one plant had an average of 23 flowers and one flower had 51 seeds. Due to the very low number of sprouted seeds of this weed the germination parameter cannot be statistically evaluated.

Invasive plants can alter pollination dynamics in invaded communities by disrupting patterns of pollinator visitation, pollen transfer dynamics (conspecific [CP] and heterospecific [HP]), and reproductive success. The direction of invasive effects (competitive, neutral, and facilitative) may be partially determined by spatial scale and species’ floral traits. Here, we investigated pollinator visitation, CP and HP receipt, and pollen tube growth for species in a C. arvense present community and non-present community at two scales. At the community-level, the effect of C. arvense on pollinator visitation varied among species. Floral symmetry seemed to explain this variation. At the floral neighborhood-level, we found competitive effects for pollinator visits and mixed effects on CP deposition. The overall structure of plant-plant HP deposition networks was slightly altered. We observed lower average centrality across shared species in the C. arvense present community suggesting C. arvense had subverted their roles as pollen donors.

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No description available.

Cirsium arvense (L.) Scop. (Californian, Canada, or creeping thistle) is an exotic perennial herb indigenous to Eurasia that successfully established in New Zealand (NZ) approximately 130 years ago. Presently, C. arvense is considered one of the worst invasive weeds in NZ arable and pastoral productions systems. The mechanism most commonly invoked to explain the apparent increased vigour of introduced weeds is release from natural enemies. The enemy release hypothesis (ERH) predicts that plants in an introduced range should experience reduced herbivory, particularly from specialists, and that release from this natural enemy pressure facilitates increased plant performance in the introduced range. In 2007 broad surveys were carried out in NZ and central Europe in order to quantify and compare growth characteristics of C. arvense in its native vs. introduced range. Additionally, permanent field plots were established in NZ and Europe where natural enemies were excluded with the use of insecticide and fungicide applications, and compared with controls (ambient natural enemy pressure). The impact of the specialist leaf-feeding beetle, Cassida rubiginosa Müller, which was recently released in NZ as a biological control agent against thistles, was also assessed. From the field surveys, significantly more endophagous herbivory was present in the native range compared to the introduced range, as predicted by the ERH. Endophagous herbivory in NZ was solely from the capitulum-feeding weevil, Rhinocyllus conicus (Frölich), and was only found in the North Island surveys. No stem mining attack was found anywhere in NZ. The proportion of shoots attacked by the specialised rust pathogen, Puccinia punctiformis (Str.) Röhl., was similar in both the native and introduced ranges. Interestingly, this has casted doubt on the idea that stem-mining vectors, such as Ceratapion onopordi Kirby, are important for transmission of the rust pathogen. Contrary to the ERH, there were no significant difference in plant performance between the native and introduced ranges, or differences could be explained by simple climatic factors. Climate tended to be more favourable for growth of C. arvense in NZ. In the permanent field plots in the native range, population growth of C. arvense was significantly greater where natural enemies were excluded, suggesting that insect herbivores and pathogens might have a regulating influence on the population growth of this plant. Furthermore, the probability of shoots transitioning to the reproductive growth stage was enhanced when insect herbivores were excluded, indicating that natural enemies might influence plant development. The biological control agent C. rubiginosa reduced the growth of C. arvense, although the impact of this herbivore was minimal in comparison to interspecific plant competition. Thus, although there is reduced specialist natural enemy pressure in NZ, the growth of C. arvense is not significantly different from in its native range. Nevertheless, there is some evidence that natural enemies in the native range might have a regulating influence on the population dynamics of the plant, and that the specialist herbivore, C. rubiginosa, can impact the plant in certain conditions.