RESUMEN
The interventions that are required for both the control and post-invasion restoration of native plant communities depends on several factors, including the efficacy of the measures that are used and how these interact with environmental factors. Here, we report on the results of an experiment on the effects of mechanical removal and herbicide application on the invasive plant Gunnera tinctoria and how an extreme weather event impacted on the invader and on the recovery of native coastal grassland communities. Both removal protocols were largely effective in eradicating mature plants, but the mechanical removal treatment resulted in a major increase in the number of G. tinctoria seedlings, which was exacerbated by the extreme event. Nine months after removal, the number of native species had recovered to c. 80% of that in uninvaded grasslands. In contrast to seedlings, mature plants of G. tinctoria showed a significant reduction in above-ground production after the extreme weather event, although these had largely recovered after six months. Overall, our results indicate that post-control restoration of the plant community may be possible without further significant management interventions. Nevertheless, since some invasive plants survived, further monitoring is required to ensure that recolonisation does not occur.
RESUMEN
Plant invasions represent a major global change in land/vegetation cover with the potential to significantly modify greenhouse gas (GHG) emissions. To get a better understanding of the impacts of terrestrial invasive plants on soil GHG emissions we report, firstly, on experiments conducted on invasive populations of the N-fixing herbaceous species Gunnera tinctoria in Ireland, and secondly, compare our results with published information based on a systematic review of the literature. For G. tinctoria populations, there was a >50% reduction in soil CO2 emissions, mainly due to a reduction in autotrophic respiration, but with little impact on annual N2O or CH4 budgets. One year after the removal of G. tinctoria, soil GHG emissions returned to values comparable to uninvaded areas and this was associated with the reestablishment of the vegetation and an increased root biomass per unit area. If G. tinctoria covered 10% of abandoned agricultural land in Ireland, this could be associated with a reduction of approximately 8% (or 4.988 Mt CO2eq y-1) of the country's national CO2 emissions. Comparisons of these results with literature values were difficult because of the often low and limited sampling effort of previous investigations, a failure to assess all three major GHGs and because of marked seasonal variations. We found 46 studies that documented results for 16 species. From the studies that measured soil respiration, it was enhanced in only 45% of cases, questioning the assumption that invasive plants always increase soil CO2 emissions. In 25 cases that analysed methane, CH4 emissions increased in 76% of them, but all of these were conducted in wetlands. In only two cases were N-fixing species associated with enhanced N2O emissions. Our results argue for more detailed and comprehensive assessments of the effect of plant invasions on GHG emissions and their global impact.
Asunto(s)
Gases de Efecto Invernadero , Dióxido de Carbono/análisis , Monitoreo del Ambiente , Efecto Invernadero , Gases de Efecto Invernadero/análisis , Especies Introducidas , Irlanda , Metano/análisis , Óxido Nitroso/análisis , Plantas , SueloRESUMEN
Responsáveis por perdas anuais consideráveis na biodiversidade dos ecossistemas naturais, as espécies exóticas invasoras causam sérios problemas à conservação, levando muitas espécies à extinção local. Este estudo analisou o efeito da cobertura de capim-colonião (Panicum maximum Jacq.) no sub-bosque de um reflorestamento dominado há mais de 17 anos por essa gramínea exótica invasora, pois resultados preliminares apontam-na como barreira para o estabelecimento de espécies nativas. Neste estudo, foram implantadas 20 parcelas de 5m x 5m (25m²) distribuídas em dois tratamentos, controle e remoção de capim-colonião, para se avaliar o impacto da capina manual sobre o sub-bosque num período de 90 dias. Dados acerca da cobertura de P. maximum e a porcentagem de abertura do dossel foram coletados. A cobertura de capim-colonião teve correlação negativa com a abundância de plantas, com a riqueza de espécies e com a abundância de espécies arbóreas. A abertura do dossel influenciou negativamente a riqueza de espécies, a abundância e a riqueza de espécies arbóreas, mas não teve correlação com a cobertura de P. maximum. Após a remoção da gramínea, tanto a abundância de regenerantes quanto a riqueza de espécies não apresentaram diferenças significativas entre os tratamentos, logo a capina manual não causou impacto negativo em curto prazo na regeneração do sub-bosque, já que poucas plantas foram acidentalmente arrancadas. Porém, um impacto positivo é esperado somente após um período maior de observação, após sucessivas remoções da herbácea invasora e aumento de chance de colonização da área por regenerantes.
Responsible for considerable annual losses of biodiversity in natural ecosystems, invasive alien species cause important conservation problems, leading native species to local extinction. This study examined the relationship among the coverage of Guinea-grass (Panicum maximum Jacq.), its manual weeding and the woody plant diversity of a restoration site. The site is a reforestation created using native species but due to spacing and species composition grass still dominates its understory more than 17 years after. Preliminary results showed that it is a barrier to the establishment of native species. In this study, we established 20 plots of 5m x 5m divided into two treatments, control and removal of P. maximum, to investigate the impact of manual weeding on the understory in a period of 90 days. Grass cover and canopy openness were also recorded. The grass cover had negative correlation with the abundance of plants, with the species richness and abundance of tree species. Canopy openness had a negative influence on the species richness, on abundance and richness of tree species, but not showed correlation with P. maximum. After grass removal, both abundance of seedling and species richness had no significant differences, so the manual weeding did not cause a negative impact in short time on the regeneration of the understory due to accidental native plant uprooting. However, a positive impact is expected only after a longer period of observation, after successive removals of invasive herbaceous and increased chance of colonization of the area by regenerating seedlings.