Patterns of alien plant invasion across coastal bay areas in southern China
An understanding of the ways in which levels of invasions by alien species are correlated with environmental factors is helpful to manage the negative impacts of these invasive species. Two tropical coastal areas in South China, Shenzhen Bay and Leizhou Bay, are national nature reserves, but they are threatened by invasive plants. Here, we investigated the level of invasion by exotic plants at both bays, and its relationship with selected environmental factors. We found a total of 34 invasive plant species, 18 of which were present at both bays; among these, 15 species were in terrestrial areas, three were at the ecotone, and one was in the mangroves. The two bays had a similar degree of invasion but were dominated by different species. Three invasive species (Ipomoea purpurea, Wedelia trilobata, and Panicum repens) were abundant at both bays, and only one species, Sonneratia apetala, was present in the mangroves. The number of alien species increased from mangrove to ecotone to terrestrial areas in both bays, while, in proportion, ecotone supported the most alien species in Shenzhen Bay. The relationships between plant invasion and habitat features depended on the variables that were used to measure the degree of invasions. In general, the occurrence of alien species was positively correlated with soil organic carbon and total N content but negatively correlated with the leaf area index and soil salinity. The biomass of alien plants was, on the other hand, positively correlated with total N and soil water content in the soil, and the density of alien plants was not correlated with habitat characteristics. Most of the alien plants originated from tropical America, but a few were from Africa and south Asia. We recommend restoration efforts that include removal of alien species, soil improvement, and the planting of native species.