Ocorrência, distribuição e impacto ecológico de plantas exóticas invasoras no Regadio do Baixo Limpopo, província de Gaza

Abstract

In Mozambique, the invasive alien plants have been introduced over the years most of them deliberately or accidentally. Studies that report the occurrence, distribution and ecological impact upon native plant diversity are very few. The present work was carried out at Lower Limpopo Irrigation System, Gaza Province, in order to survey invasive alien plants and assess their associated impacts on native species. The samplings were taken along the Limpopo River, channels and drainage ditches, in every 2 or 3 km. In each sampling site, data of temperature, pH and electrical conductivity of water were collected. The other variables were obtained in loco and using the National Soil Map. The abundance and coverage of the species was determined using a quadrat of 1 m 2 , and all plant species found were recorded. Species identification was performed by a botanical and field guides. The ecological impact was evaluated by the generic impact scoring system (GISS). The data were analyzed in MS Excel to determine phytosociological parameters, in iNEXTOnline to compare α and β diversity through the Shannon, Simpson and Jaccard indexes, and R for statistical analysis of data upon species diversity in the invaded and not invaded quadrats by invasive alien species. The results of this survey showed that 71 invasive species (74,65% terrestrial and 25,35% aquatic) belonging to 29 families occur in the RBL. The Poaceae and Asteraceae families were the most represented in invasive species. Together, they contributed with more than 50% of sampled individuals. The most abundant species in area were Phragmites australis, Phragmites mauritianus and Echinochloa pyramidalis. The richness and diversity of invasive species differed between the districts, being higher in Xai-Xai, Chongoene and Limpopo districts when compared to the Chibuto district. The same districts were the most similar in terms of invasive species. About 38.89% of the sampled species are widely distributed, 20.83% in a restricted way and 40.28% occur in a localized way and with unitary individuals. Of the variables considered, the land use type, slope, temperature and pH of water were more influential to explain the abundance and distribution of the invasive species. By the GISS were scored 91.55% of the invasive species inventoried and Lantana camara scored the highest impact score. The species with the lowest impact score were Hibiscus cannabinus and Oxalis latifolia. The most common ecological impact mechanism was competition. The not invaded quadrats by the invasive species presented major native species diversity