Abstract
Invasive alien species have distressing impacts on native biota, causing decline or even extinctions of native species, and negatively affecting ecosystems. All major invasions are due to the actions of humans such as deliberate introductions or escapes, and hitchhiking with global trade of species to other continents. Though majority of introductions have only minor impacts to the ecosystem, some of them led to numerous problems. 48 exotic species have been recorded from Saudi Arabia; of which 9 are recorded for the first time from Saudi Arabia. Among these, the species that potentially damaging the biodiversity or altering the ecosystems in general are: Argemone ochrolecuca, Nicotiana glauca, Opuntia dellenii, Opuntia ficus-indica, Prosopis juliflora and Trianthema portuiacastrum. Among these, P. juliflora has been observed in lower altitudes with a density of more than 6%/hectare followed by O. dellenii and N. glauca in areas above 1000 m. Mountains and wadis have the highest values in terms of species richness, cover and exotic species impact. Analysis showed that environmental and diversity variables have high significant variation between habitats. Invasive and other exotic species are correlated positively with altitude and most diversity indices except with species dominance which are correlated negatively. (C) 2015 Elsevier Ltd. All rights reserved.