Testing the importance of native plants in facilitation the restoration of coastal plant communities dominated by exotics

Abstract

Casuarina equisetifolia was introduced to China in 1897 from Australia to reduce coastal erosion. It grows vigorously and has spread over much of the southern and southeastern coast, from Zhejiang to Guangxi, over a range of more than 10° of latitude. To date, little is known about its interactions with native species in the coastal zone.We used a field experiment to study how the understorey species diversity and soil conditions in monoculture stands of C. equisetifolia were influenced by different native plant species. We also examined the effects of interplanting native species on plant numbers, leaf area index (LAI), and aboveground biomass accumulation. We planted three native species (Hibiscus tiliaceus, Melia azedarach and Calophyllum inophyllum) at two initial densities in stands of C. equisetifolia.Over a period of ten years, the density and aboveground biomass were relatively low in plots planted with three native species compared to plots that were not planted. In contrast, understory diversity and soil conditions were relatively high where native species were added. Moreover, the number of dead tree, aboveground biomass increment, and diameter growth had significant difference among different native tree species because of their different natural characteristics.The fast-growing pioneer species, M. azedarach, had a positive effect on LAI, regeneration, shrub diversity and grass coverage than the other two native species, and M. azedarach was most effective in plots that were initially planted with higher densities. The pioneer plant H. tiliaceus had more individuals and greater aboveground biomass than others native species. The later-succession species C. inophyllum had the smallest effect on the development of understory vegetation and soil conditions over 10-yrs among three native plants. For different native planted species, M. azedarach showed good effects on the average annual aboveground biomass and DBH increment, and C. inophyllum had the least dead number in coastal environments.In summary, C. equisetifolia and native species have facilitation relationships that differ according to the species, and coastal conservation managers should shift from their traditional focus on C. equisetifolia afforestation to the recognition of multi-species configuration.