Ecological Studies On The Controlling Of An Invasive Alien Plant Spartina Alterniflora

Biological invasion has received considerable attention recently due to their increasing impacts on local ecosystems and is becoming one of the six most serious environmental problems that may influence the future economical and social development. Since introduced into the Chongming Dongtan Nature Reserve in 1995, Spartina alterniflora has rapidly expanded and seriously threatened the biodiversity there. During 2005 and 2006, a field experiment of controls, including digging tillage, breaking rhizome, mowing, and biological substitute, on S. alterniflora was conducted to search effective measures for controlling this invasive plant. The growth parameters of plant density, height, cover, leaf area index (LAI), stem diameter, aboveground biomass, fruiting number, fruiting rate and inflorescence length were used to evaluate the efficiency of different treatments. The major findings are summarized as follows.1) S. alterniflora has invaded rapidly into the intertidal zones mainly via asexually spreasing at Chongming Dongtan in recent years. It was hypothesized that the different treatments on the vegetative rhizomes would have different effects on the re-growth of S. alterniflora.The results from the treatment of digging tillage (20 cm, 40 cm and 60 cm) showed that the density of S. alterniflora began to increase from July for the treatment of digging tillage, while the plant density, mean height, cover, aboveground biomass and fruiting number were still significantly lower than those of the control (P<0.05), but fruiting rate and inflorescence length met those of the control. There were no significant differences between the different treatments of the three depths (P>0.05). In the second growing season, the differences between the treatment and the control were not as significant as in the first growing season and there were no significant differences in the end of the second growing season, except that the fruiting number and fruiting rate of S. alterniflora were significant higher than those of the control, and the cover and aboveground biomass of 60 cm depth treatment were much lower than that of the control (P<0.05).The treatment of breaking rhizome significantly inhibited the growth of S. alterniflora in the first growing season and the inhibition increased with the depth of the treatment. However, the inhibition on S. alternijlora's growth disappeared after two growing seasons and there were no significant differences among the treatments and the control (P>0.05).The treatments on the rhizomes of S. alternijlora in this study resulted in many native species occurring in the first year, including Assiminea violacea, Cerithiidea largillierli, Sesarma denaani, Ilyrplax deschampsi, Boleophthalmus Pectinirostris L., and one native species of plant: Scirpus mariqueter, suggesting that it may facilitate the establishment of the native community. However, the aboundance and density of benthic macroinvertebrates decreased significantly with the rapid enhancement in cover of S. alterniflora in the second year.2) The optimal period of controlling invasive species is a key factor to succeed in removing the invaders. The treatment of mowing on control of S. alterniflora occurred in every month throughout one growing season (except April), and included repeated mowing: two and three times. The results showed that the treatment of mowing significantly inhibited both vegetative growth and sexual reproduction of S. alterniflora in the first growing season (P<0.05), while the treatment of mowing in March significantly promoted the growth of S. alterniflora, including higher cover, density, aboveground biomass, fruiting number and fruiting rate compared to those of the control (P<0.05).In the end of second growing season, both vegetative growth and sexual reproduction of S. alterniflora recovered in some extent. The treatments occurred in June, July, August, September, and repeated mowing (two and three times) significantly inhibited its vegetative growth (P<0.05). However, the sexual reproduction of S. alterniflora under all the treatments met or exceeded that of the control, only the fruiting number recorded in the treatment of mowing in August was significantly lower than that of the control (P<0.05). The treatment of mowing in August had proven to be the most effective, so it might be the suitable time for controlling.3) Biological substitute is to use native species, economically or ecologically benefit to the native ecosystems, as a biological control agent to replace the invasive species. In the experiment of biological substitute, S. alterniflora was first removed by the treatments of both digging tillage and breaking rhizome, and then Phragmites australis was transplanted into the treated plots. The results showed that the transplanted P. australis kept a relatively high survival and occupied certain room among the population of re-grown S. alterniflora during the two growing seasons. Both plant height and fruiting rate of P. australis increased considerably in the second growing season.The results from this study indicated that S. alterniflora has a strong capacity to withstand physical stresses or disturbances and regrow rapidly. It is necessary to take into account of frequency, intensity and season of these measures to achieve a feasible strategy for controlling the invasion of S. alterniflora in the nature reserve.