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
