Impacts of Panicum maximum Jacq. invasion and its manual weeding on the wood plant regeneration in the understory of a restoration site

Abstract

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.