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Estuarine, Coastal and Shelf Science 92 (2011) 103e110

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Estuarine, Coastal and Shelf Science

journal homepage: www.elsevier .com/locate/ecss

The application of cutting plus waterlogging to control Spartina alternifloraon saltmarshes in the Yangtze Estuary, China

Lin Yuan a, Liquan Zhang a,b,*, Derong Xiao a, Huamei Huang a

a State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 3663 Zhongshan Road North, Shanghai 200062, Chinab Shanghai Key Laboratory of Urbanization and Ecological Restoration, East China Normal University, 3663 Zhongshan Road North, Shanghai 200062, China

a r t i c l e i n f o

Article history:Received 26 October 2010Accepted 15 December 2010Available online 23 December 2010

Keywords:Spartina alterniflorasaltmarshesinvasiongrowthreproductionYangtze Estuary

* Corresponding author. State Key Laboratory of EstEast China Normal University, 3663 Zhongshan RoChina.

E-mail address: lqzhang@sklec.ecnu.edu.cn (L. Zha

0272-7714/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.ecss.2010.12.019

a b s t r a c t

Control and eradication of the exotic and invasive plant Spartina alterniflora within the ChongmingDongtan nature reserve, Shanghai, China, is vital for the management and conservation of the salt-marshes. A demonstration project was established using waterlogging and cutting to control this invasivespecies. Results from 2007 to 2008 showed that, although the managed waterlogging significantlyreduced biomass and seed production of S. alterniflora at an early stage, the species subsequently showedrapid adaptation to the long-term waterlogging stress. Thus, managed waterlogging alone was insuffi-cient for the effective eradication of S. alterniflora. However, managed waterlogging for around 3 months,combined with cutting the above-ground part of S. alterniflora at a key stage (flowering period in July),controlled and eradicated the plant successfully. Both the above-ground and below-ground parts of S.alterniflorawere killed and the plants began to decompose after 3 months. Furthermore, there was no re-growth of the emergent part of S. alterniflora in the following years. However, once the impounded waterwas released restoring the natural hydrodynamic regime of the saltmarshes, the seeds and seedlings ofS. alterniflora reinvaded the controlled site from the neighboring areas and the S. alterniflora communitywas re-established. Thus, after eradication of S. alterniflora, control measures should be maintained toprevent the re-establishment of S. alterniflora. The results of this demonstration project indicatea potentially useful and effective approach for the control and management of large-scale invasion byS. alterniflora on saltmarshes in the Yangtze Estuary, China.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Biologically invasive species represent one of the most seriousenvironmental problems that may influence future economical andsocial development (Gewin, 2005; Mooney et al., 2005). Spartinaalterniflora (smooth cordgrass), which is native to the Atlantic andGulf coasts of North America, is a perennial saltmarsh grass thatperforms important ecological functions in its native ecosystems(Simenstad and Thom,1995). Furthermore, due to its great capacityto reduce tidal wave energy, mitigate erosion, trap sediments andprotect the seacoast, S. alterniflora has been widely introduced tomany coastal and estuarine regions of the world as a species forecological engineering (Mitsch et al., 2002; Chung et al., 2004;Balletto et al., 2005; Weishar et al., 2005). Spartina alterniflorawas first introduced to the Chongming Dongtan nature reserve,

uarine and Coastal Research,ad North, Shanghai 200062,

ng).

All rights reserved.

Shanghai, China in 1995, for the purpose of trapping sediments andencouraging saltmarsh accretion and expanded rapidly thereafter.After its introduction, the area of S. alterniflora increased to almost27% of the total intertidal saltmarsh vegetation in ChongmingDongtan (Huang et al., 2007).

Evidence has recently been presented that Spartina alternifloramay spread rapidly, out-competing native plants and invading nativesaltmarsh communities, threatening the native coastal ecosystems,and causing the decline of native species richness (Callaway andJosselyn, 1992; Daehler and Strong, 1996; Huang et al., 2008). Inthe Yangtze Estuary, Huang et al. (2008) reported that invasion ofS. alterniflora had out-competed the native plants of Phragmitesaustralis and Scirpus mariqueter. The rapid expansion of S. alterniflorahad changed the species composition of benthic communities(Wang et al., 2010). The habitat suitability for migratory birds hadbeen seriously threatened (Tian et al., 2008).

Various measures have been suggested to control or eradicateSpartina alterniflora, including methods of chemical control (Patten,2002; Liu et al., 2004), physical or mechanical techniques (Fridet al., 1999; Li and Zhang, 2008) and biological control (Wu et al.,

L. Yuan et al. / Estuarine, Coastal and Shelf Science 92 (2011) 103e110104

1999; Grevstad et al., 2003). Methods of physical control applymanual work or mechanical devices to cut, burn, prune, excavate,dredge, flood and drain the S. alterniflora plants, in order to restricttheir growth, hinder their respiration and photosynthesis andfinally suppress or kill them (Hedge et al., 2003). Chemical controlsuse herbicides that may impact on the soils or local ecosystems,while biological controls inevitably introduce some naturalenemies that may bring a further potential invasion and oftena long time is required in order to validate their efficiency (Kilbrideet al., 1995; Patten, 2002). As a result, methods of physical controlhave usually been the first option chosen. However, where a singlephysical control measure has been employed, it has often beenreported as inefficient and instead combined measures have beenproposed (Kriwoken and Hedge, 2000; Hammond and Cooper,2002; Major et al., 2003; Li and Zhang, 2008).

In this study, a demonstration project was established usingmanaged waterlogging and cutting to control Spartina alternifloraat the Chongming Dongtan nature reserve during 2007e2008. Theobjectives of the study were: (1) to find effective techniques forcontrolling invasive plant of S. alterniflora; (2) to obtain usefulinsights into the means by which S. alterniflora reinvades aftercontrol; (3) to provide useful strategies to inhibit the large-scaleinvasion of S. alterniflora and thus encourage biological diversity onsaltmarshes in the Yangtze Estuary.

2. Materials and methods

2.1. Study area

The study area is located on the Chongming Dongtan naturereserve (31�250e31�380N, 121�500e122�050E) (Fig. 1), one of thelargest nature reserves for migratory birds in East Asia. It is situatedat the mouth of the Yangtze Estuary in eastern China and at themiddle range of the eastern migratory routes of the Asia and Pacificregion. The wetlands were listed in the Chinese ProtectedWetlandsreport (1992), and were designated as internationally importantunder the Ramsar Wetlands Convention (2001) and as a nationalnature reserve in 2005 (Gao and Zhang, 2006).

The region of mouth bars in the estuary and the submerged deltanearby the estuary are the major locations for sedimentation of thevery large amount of silt brought by the Yangtze River. The eastern

Fig. 1. The location of the Chongming Dongtan nature reserve and the experimental desiflowering period plus managed waterlogging, Block W e managed waterlogging alone, Blregime in 2008 after managed waterlogging in 2007, Block CK e the control.

fringe of the nature reserve has been shown to be advancing at a rateof between150and300 mper year (Gao andZhang, 2006). Accordingto theobservationdataovera 30-yearperiod from1978 to2008at theWaigaoqiao tidal gauge station, the localmean sea level is 2.17 m, themean tidal range 2.48 m and the maximum tidal range 4.43 m.

The total area of the nature reserve is 32,610 ha and threedistinct zones of saltmarsh vegetation, related to elevation, can beidentified, stretching from the 1998 inland dyke and moving east-wards towards the low tide. The tidal flats with an elevation of lessthan 2 m are characterized by bare mudflats without any vascularplants. The tidal flats between 2.0 and 2.9 m elevation are domi-nated by the Scirpus mariqueter community. Above 2.9 m, plantcommunities are dominated by a native plant Phragmites australisand an exotic plant Spartina alterniflora (Huang et al., 2007).

The result of our previous study on the spatio-temporaldynamics of saltmarsh vegetation for the nature reserve (Huang,2009) indicated that after the introduction of Spartina alterniflorain 1995, this species has rapidly invaded large areas of the naturereserve, out-competing the native species due to its strongercompetitive capacity, wider ecological niche and assistance in therapid accretion of intertidal flats (Fig. 2).

2.2. Demonstration site and experimental design

A field demonstration project site (200 m� 250 m, total area5 ha) was established in the northern experimental zone of theChongming Dongtan nature reserve (N 31�350, E 121�530) (Fig. 1).The elevation of site was ca 3.60 m and was covered by mono-dominant community of Spartina alterniflora with some scatteredsmall patches of Phragmites australis. The experimental designconsisted of four blocks, each 50 m� 250 m. The Block 1 treatmentwas cutting of S. alterniflora plus managed waterlogging, while inBlock 2 S. alterniflorawas subjected to manage waterlogging alone.Block 4 represented the control (CK) with no treatment (Fig. 1). Theexperimental design had no independent replication duo to thelarge-scale demonstration project and the difficulty of completingmultiple blocks for each treatment. Prior to the commencement ofthe experiment, vegetation and soil surveys were carried out acrossall four blocks and the results indicated that there were no signif-icant differences among these blocks (Yuan et al., 2008). Theexperimental design could still be adequate for the goals of this

gn for the demonstration project site. Block CW e cutting Spartina alterniflora at theocks CWR and WR e the cofferdam was broken to restore the natural hydrodynamic

Fig. 2. The spatio-temporal dynamics of saltmarshes vegetation and invasion history of Spartina alterniflora during 1998e2008 at the Chongming Dongtan nature reserve.

L. Yuan et al. / Estuarine, Coastal and Shelf Science 92 (2011) 103e110 105

study and informative along with the limitations of such data, asthe area was homogenous silt and vegetation.

In March 2007, the dead above-ground parts of Spartina alter-niflora from previous year were removed from all four blocks,while those of Phragmites australis were left uncut. An earthcofferdam, 1 m in height, was built up around Block 1 and Block 2to keep them waterlogged. The water depth was maintained at30e50 cm by pumping tidal water from the nearby ditch when-ever necessary. During the flowering period in July, the above-ground biomass of S. alterniflorawas cut level to the surface andwaskept waterlogged in Block 1 (treatment CW), while the S. alterniflorain Block 2 remained uncut and was only subjected to waterlogging(treatment W) (Fig. 1).

In March 2008, after the first 12-months of managed water-logging, a new cofferdamwas constructed within Blocks 1 and 2 tocreate blocks CWR and WR, each 50 m� 100 m in size. The easternand western sides of the cofferdams for CWR and WR blocks werebroken to release the impounded water and the previous naturalhydrodynamic regime was restored (Fig. 1). In contrast, the CWandW blocks remained waterlogged for the whole of 2008.

2.3. Field sampling and measurement

In April, June and October 2007, the growth of Spartina alterni-florawas monitored in blocks CW, W and CK, and in April, July andOctober 2008 in the blocks CW, W, CWR, WR and CK. The above-

L. Yuan et al. / Estuarine, Coastal and Shelf Science 92 (2011) 103e110106

ground biomass (leaf, stem and spikelet) of S. alterniflora was har-vested in five replicates 1 m� 1 m quadrats, selected at randomwithin each treatment block and sampling date, respectively. Thebelow-ground biomass of S. alterniflora was sampled by digginga soil block, each 0.25 m� 0.25 m� 0.4 m, from every quadrat ineach treatment block and sampling date, respectively. Both theabove-ground and below-ground biomass of S. alterniflora weredried in the laboratory at 80 �C to a constant weight and convertedto DW g/m2.

In late October 2007 and 2008, the total number of culms andfruiting culms of Spartina alterniflorawas countered in five replicatequadrats, each 1 m� 1 m, selected at random in each treatmentblock. The seed number per spike was recorded by selecting fiveindividuals at random in each quadrat. The seeds were taken to thelaboratory, air-dried and weighted. The seeds were tested forviability using a tetrazolium staining method (Jessie and Moore,2008).

To monitor the re-invasion of Spartina alterniflora, in March2008,10 plots, each 1 m� 1 m, were established at random in blockCWR. Those seedlings that reinvaded into the block were countedand marked during May 2008. The ramets (individuals) of S. alter-niflora were counted in late October 2008 to estimate the seedlingsurvivorship and asexual propagation by tillering and rhizoming.The canopy height was measured, and the ramet density, fruitingculms and seed production of S. alterniflora were counted to eval-uate the growth and sexual reproduction of reinvaded S.alterniflora.

2.4. Data analysis

The data collected from field and laboratory measurementswere analyzed using a one-way ANOVA to test for significantdifferences between and among the control and the treatments.The one-way ANOVA was implemented using SPSS11.0 and OriginLab TM 7.5 packages.

Fig. 3. The effects of different treatments on the growth of S. alterniflora during the years 2002008 and D in October, 2008.

3. Results

3.1. Growth of Spartina alterniflora

The effects of the various treatments on the growth of Spartinaalterniflora during the years 2007e2008 in the demonstrationproject site are illustrated in Fig. 3. The managed waterloggingalone (W) did not control S. alterniflora effectively (Fig. 3 e right ofeach image). The managed waterlogging plus cutting at floweringperiod in July (CW and Fig. 3B) controlled and eradicated S. alter-niflora effectively and therewas no re-growth of S. alterniflora in theblock CW (upper left side of Fig. 3). While the CWR was reinvadedby S. alterniflora in 2008 after the cofferdam was broken to restoreinto the natural hydrodynamic regime (Fig. 3D).

Themeasurements of Spartina alterniflora growth in the differentblocks during 2007e2008 are presented in Fig. 4. After onemonth ofwaterlogging, there were no significant differences in the totalbiomass values of S. alterniflora between the blocks CW (1667.1 g/m2),W (1723.5 g/m2) andCK (1716.0 g/m2) (P> 0.05). Thebiomass ofS. alterniflora was mainly allocated below ground (roots andrhizomes) and theproportions of below-groundbiomasswere 91.7%,91.9% and 92.2% for the ramets in CW,WandCK, respectively. Duringthe fast growing season in June 2007, there were also no significantdifferences in total biomass of S. alterniflora among CW (1277.5g/m2), W (1360.9 g/m2) and CK (1406.1 g/m2) (P> 0.05), while theproportions of biomass were mainly allocated above ground. Aftercutting the above-ground parts of S. alterniflora on CW during theflowering period in July 2007, there was no re-growth of ramets andthe below-ground parts were killed and began to decompose inOctober 2007. The total biomass values of S. alterniflora onWand CKin October 2007 were 3161.2 g/m2 and 4037.4 g/m2 and the propor-tions of above-ground biomass were 68.7% and 46.5% respectively,which indicated that waterlogging alone could significantly reducethe growth of S. alterniflora and the proportion of below-groundbiomass (P< 0.05) during the first growing season (Fig. 4).

7e2008 at the demonstration project site. A in July 2007, B in November 2007, C in June

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Fig. 4. Effects of different treatments (for legends see Fig. 1) on the biomass of Spartinaalterniflora during the years 2007e2008 in the demonstration project site.

L. Yuan et al. / Estuarine, Coastal and Shelf Science 92 (2011) 103e110 107

During the second growing season in 2008, there was no re-growth or seedlings of Spartina alterniflora in block CW and thebelow-ground parts of S. alterniflora decomposed completely(Fig. 4). As S. alterniflorawas killed in 2007, there was no biomass ofS. alterniflora in block CWR in April 2008. The total biomass valuesof S. alterniflora within blocks W and WR in April 2008 were2736.2 g/m2 and 2553.9 g/m2 respectively, whichwere significantlyhigher than the 2174.3 g/m2 within block CK (P< 0.05), and theproportions of below-ground biomass were 66.6%, 70.7% and 82.6%for the ramets within blocks CW, W and CK, respectively. At theflowering period in July 2008, the total biomass values of S. alter-niflora increased rapidly within blocks W, WR and CK, to 2146.1g/m2, 1916.3 g/m2 and 1901.4 g/m2, respectively, and differencesamong these blocks were not significant (P> 0.05). At the end ofthe growing season in October 2008, the total biomass values ofS. alterniflora within blocks W, WR and CK were 3467.6 g/m2,2948.3 g/m2 and 3547.6 g/m2, respectively, and there were nosignificant differences among these blocks (P> 0.05). The propor-tions of total biomass allocated to sexual reproduction and below-ground storage increased considerably, amounting to 40.5%, 45.9%and 46.0% of total biomass within the blocks W, WR and CK (Fig. 4).

It is worth noting that, after breaking the cofferdam to restorethe natural hydrodynamic regime, seedlings of Spartina alterniflorafrom the neighboring invaded area reinvaded block CWR and afteronly one growing season, the total biomass of S. alterniflora reached879.8 g/m2, and the proportions of total biomass allocated to sexualreproduction and below-ground storage amounted to 56.9% (Fig. 4).

3.2. Reproduction of Spartina alterniflora

The effects of waterlogging on the reproduction of Spartinaalterniflora are presented in Fig. 5. As S. alterniflora was eradicatedwithin the block CW, there was no reproduction of S. alternifloraduring 2007e2008. At the end of the growing season in October2007, the seed production of S. alterniflora within the block Wamounted to 7192.2 seeds/m2 and was lower than 19,764.6 seeds/m2 within block CK (P< 0.05). The seed weight and seed viabilitywithin block W were 3.7 g/1000 seeds and 21.6%, and lower than4.6 g/1000 seeds and 37.2% within block CK, respectively (P< 0.05).

At the end of the growing season in 2008, the seed production ofSpartina alterniflora within blocks W and WR amounted to8110.3 seeds/m2 and 8696.0 seeds/m2 respectively, which wereboth still lower than the figure of 19,029.0 seeds/m2 within blockCK (P< 0.05). While the seed weight and seed viability of S. alter-niflora within block W were 4.2 g/1000 seeds and 28.3%, withinblock WR, they were 4.1 g/1000 seeds and 27.9%, and within blockCK they were 4.4 g/1000 seeds and 36.0%, and there were no

significant differences in the seed weight and seed viability amongW, WR and CK (P> 0.05) (Fig. 5).

3.3. Re-invasion of Spartina alterniflora

There was no re-invasion of Spartina alterniflora within blockCW during the year 2008. In contrast, within block CWR, afterbreaking the cofferdam to restore natural hydrodynamic regime,a density of 5.6/m2 seedlings of S. alterniflora was recorded in May2008 and the seedling survivorship reached 81.4% (Table 1). Theestablished seedlings of S. alterniflora showed strong tilleringability and at the end of the growing season in October 2008, theramet density amounted to 158.0/m2, the ramet height was 81.5 cmand the total biomass reached 879.8 g/m2, although these valueswere lower than the 265.0/m2, 151.4 cm and 3547.6 g/m2 respec-tively, recorded within block CK (P< 0.05) (Table 1). The seedproductionwas 5050.7/m2 and the seed viability 20.4%, which werelower than the values of 19,029.0/m2 and 36.0% respectively withinblock CK (P< 0.05) (Table 1).

4. Discussion

4.1. Effectiveness of control measures

As an invasive plant on saltmarshes in the Yangtze Estuary,Spartina alterniflora has a strong capacity to withstand physicalstress or disturbance (Zhang et al., 2006; Li and Zhang, 2008).Waterlogging can interrupt gas exchange between a plant and theatmosphere, create an anoxic condition for plant tissues and inhibitplant normal growth and development (Pezeshki, 2001; Xiao et al.,2005; Yuan et al., 2008). Some wetland plants are capable ofincreasing the length of their stems to adapt to increased waterdepth (Ellison and Farnsworth, 1998; Lai and He, 2007) or adjustingtheir biomass allocation among the different tissues to accommo-date waterlogging stress (Anderson and Pezeshki, 2001; Bangeet al., 2004; Darby and Turner, 2008; Montemayor et al., 2008). Inthis study, the managed waterlogging alone reduced biomass andseed production of S. alterniflora during the first growing season.However, plant S. alterniflora demonstrated that it could adapt tothe waterlogging stress by increasing its height. During the secondgrowing season, S. alterniflora showed a rapid adaptation to thelong-term waterlogging stress, which was in agreement with thephenomenon of compensation or over-compensation (Li andZhang, 2008). Thus, long-term waterlogging alone (the results inBlock W) had little effect on the established plants and could notcontrol or eradicate S. alterniflora effectively.

The results from a previous field experiment (Li and Zhang,2008) also showed that control measures of digging and tillage,breaking of rhizomes and cutting appeared to have a suppressingeffect on the growth of Spartina alterniflora in the first growingseason, but could not effectively control or inhibit it in the longterm. The control measure of cutting at the start of growing season(March) would greatly promote the growth of S. alterniflora, whilecutting performed during the growing season (from May toSeptember) could subsequently suppress the growth of S. alterni-flora to a certain extent. However, S. alterniflora was shown to becapable of recovering rapidly and the plant density, coverage andabove-ground biomass could return back to the same level of thecontrol after only one growing season. As a result, the treatment ofcutting alone could only have a suppressive effect on the growth ofS. alterniflora in one growing season and could not effectivelycontrol or inhibit this plant in the long term (Li and Zhang, 2008).

The results from this study indicated that managed water-logging combined with cutting the above-ground part of S. alter-niflora at a key stage (the flowering period in July) could control and

aa

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Fig. 5. Effects of managed waterlogging (for legends see Fig. 1) on the reproduction of Spartina alterniflora (Error bars represent �SE; n¼ 5; the different letters indicate significantdifferences at P< 0.05 level).

Table 1Spartina alterniflora community characteristics and reproduction parameters afterre-invasion in October 2008 (mean� S.E); the different letters indicate significantdifferences (P< 0.05) between blocks CWR and CK (for legends see Fig. 1).

Parameters CWR Block CK Block

Seedling density (no./m2) 5.6� 2.2 e

Seedling survivorship (%) 81.4� 1.3 e

Ramet density (no./m2) 158.0� 21a 265.0� 35bRamet height (cm) 81.5� 15.1a 151.4� 24.2bTotal biomass (g/m2) 879.8� 147.5a 3547.6� 716.9bSeed production (no./m2) 5050.7� 2230.7a 19,029.0� 7718.8bSeed viability (%) 20.4� 3.3a 36.0� 9.8b

L. Yuan et al. / Estuarine, Coastal and Shelf Science 92 (2011) 103e110108

eradicate this plant effectively within one growing season, andthere was no re-growth S. alterniflora in the following growingseasons (the results in Block CW). The effects of cutting at theflowering period could be explained by phenotypic plasticity indifferent growing stages (Li and Zhang, 2008). Most energyproduced by photosynthesis during the growing season wasdevoted to sexual reproduction but when this was then removed bycutting, less energy and material could be devoted to the rhizomesand roots and the growth thereafter would be inhibited. It was themost vulnerable stage of the growth of S. alterniflora and by inte-grating cutting with waterlogging, successful eradication ofS. alterniflora was achieved.

4.2. Re-invasion of Spartina alterniflora

Spartina alterniflora is a clonal and perennial saltmarsh grass,and both sexual reproduction by seeds and asexual propagation bytillering and growth of rhizomes enable the species to invaderapidly within a new habitat (Davis et al., 2004; Montemayor et al.,2008; Xiao et al., 2010). The invasion of S. alterniflora on salt-marshes in the Yangtze Estuary is dependent on the emergingempty niches (Huang et al., 2008; Xiao et al., 2010). The process ofre-invasion of S. alterniflorawithin block CWR in this study were inagreement with the conclusions described above. After eradicatingS. alterniflora on block CW, a new empty niche was created. Oncethe cofferdam impounding the water was broken to restore the

natural hydrodynamic regime of wetlands, the seeds and seedlingsof S. alterniflora brought by tidal water from the neighboringinvaded area could reinvade into block CWR. With a high seedlingsurvivorship and strong tillering capacity, S. alterniflora successfullyreinvaded these controlled sites. Therefore, continuation of controlmanagement practices is nevertheless required after the successfuleradication of S. alterniflora by combining waterlogging withcutting.

4.3. Strategies to control Spartina alterniflora

After its initial introduction to Chongming Dongtan, Spartinaalterniflora has expanded rapidly and increased to 1377.5 ha,

L. Yuan et al. / Estuarine, Coastal and Shelf Science 92 (2011) 103e110 109

covering almost one-third of the total intertidal saltmarsh in theChongming Dongtan nature reserve (Huang, 2009). Control anderadication of this invasive plant S. alterniflora at the ChongmingDongtan nature reserve is important and necessary for biodiversityconservation. The results from this demonstration project providevaluable insights into which approaches to the strategic control ofS. alterniflora are likely to be successful.

Based on the evidence drawn from this demonstration project,a realistic strategy for controlling and managing a large-scaleinvasion of Spartina alterniflora in the nature reserve would be bycombining cutting at the flowering period (July) with waterloggingfor around the following three months. On the saltmarshes in theYangtze Estuary, a native species of Phragmites australis shares thesame niche with the exotic S. alterniflora. Once either of these twospecies occupied the new habitat, they do not out-compete andreplace each other, a result which conforms to the classical space-preemptionmodel (Huang et al., 2008). The scattered small patchesof P. australis which were left uncut in block CW were negativelyaffected and could propagate under the waterlogged environment.Therefore, P. australis would be an ideal biological substitute aftereradication of S. alterniflora on the controlled area to prevent re-invasion of this exotic plant.

Previous studies have also indicated that efforts to controlSpartina alterniflora should not only be located in the areas ofcurrent growth of this invasive species, but also on the advancingwave fronts of range expansion (Xiao et al., 2010). Building earthcofferdams to impound water and keep waterlogging in the areaswhere control is required has not only been proved to be aneffective and economical measure to control S. alterniflora, but alsocan serve as an isolation barrier to stop the rapid geographicalspreading of this plant. The cost of control and management ofS. alterniflora in this demonstration site was approximately 500dollar per hectare, which included building earth cofferdams,pumping tidal water and labors. The cost could be reduced furtherwhen applied in a larger area. Using the successful combinedcontrol strategies drawn from this demonstration project, a plan tocontrol and manage the large-scale invasion of S. alterniflora in the24 km2 area within the Chongming Dongtan nature reserve hasbeen drawn up by local government officers and nature reservemanagers and will be implemented in the near future.

Acknowledgement

The authors would like to thank members of the EcologicalSection of the State Key Laboratory of Estuarine and CoastalResearch, East China Normal University, for their assistance withthe collection of field data. We also thank Professor Martin Kent,School of Geography Earth and Environmental Sciences, Universityof Plymouth, England, for valuable comments and linguisticchecking. The research was funded by the Global Change ScientificResearch Program of China (2010CB951204), National ScientificFoundation for Distinguished Young Scholars of China (40901237)and “111 Project” (B08022).

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