Non-native and invasive alien plants on fluvial islands in the São Francisco River, northeastern Brazil

Abstract

This paper is the result of a survey of the alien flora present on fluvial islands in the São Francisco River, northeastern Brazil. The floristic similarities between the islands wereassessed, as well as the relationship between area size and species richness. The study covered eight islands in the São Francisco River Valley and was carried out in a period of eight months. Thirty one alien species were registered, six of them (Amaranthus viridis, Calotropis procera, Cenchrus ciliaris, Enneapogon cenchroides, Prosopis pallida and Ricinus communis) present on all islands. The highest number of invasive alien species (26) was recorded on Massangano Island. The floristic similarity between the islands varied between medium and very high, while the number of alien species present was positively correlated with area size. The study demonstrates that the biodiversity on these eight fluvial islands is endangered, especially due to the presence of alien species capable of invading natural areas.

Exotic Invasive Flora Evaluation on Different Environments and Preservation Conditions From an Area Belonging to Caatinga, Petrolina, Pe

“…The exotic species diversity observed was similar to that found by Fabricante et al (2015) in a survey performed in São Francisco river islands, which was superior to the values found in other similar works (Martins et al 2007;Santana and Encinas 2008). However, it was lower than that found in a floristic catalog realized under the São Francisco River Integration Project (PISF) (Fabricante and Siqueira-Filho, 2012b).…”

“…The high representativeness of the families Poaceae and Fabaceae is common in surveys of exotic flora (Almeida et al 2014;Fabricante et al 2015;Fabricante et al 2012b;Horowitz et al 2013) although in a survey of exotic trees, the number of species are well distributed among all families (Santana and Encinas 2008). However, because they are tree, it excludes grasses that have the greatest representativeness in the other studies.…”

“…This number becomes significant when considers the scales used by both studies: the experimental area corresponds to 3.6 km², while the total area of the Caatinga is equal to 800,000 km² (Almeida et al 2014). Catharanthus roseus, Cenchrus echinatus and Eragrostis tenella were listed in other surveys in the region (Fabricante et al 2015;Fabricante and Siqueira-Filho 2012b).…”

“…From the catalogued species, 19 were sampled by Fabricante et al (2015). The proximity among the areas should be the main reason for the high species number in common, added the fact that most of the species are widely distributed in the Brazil Northeaster and many in whole country (List of Species of the Brazilian Flora, 2017).…”

“…It was considered to be an exotic invasive those species that are able to reproduce in an effective way to maintain a viable population, and that is able to disperse for areas far from its original introduction location and to establish there, invading the new region (Moro et al 2012). This classification was done through field observations and consulting to scientific articles (Almeida et al 2014;Fabricante et al 2015;Fabricante and Siqueira-Filho 2012b;Horowitz et al 2013), as well as consulting databases on the subject (Bionet-Eafrinet 2017; Cabi 2017; I3N Brasil 2017; ISSG Global Invasive Species Database 2017). The species were also classified according to their habit (herbs, bushes, climbers and trees) and to their origin.…”