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Sonneratia apetala,a native mangrove species in India,Bengal and Sri Lanka,was introduced in 1985 to Dongzhaigang Mangrove Nature Reserve in Hainan Island from Sundarban,southwest of Bangladesh.The trees beared fruits 3 years later.Then it was further introduced from Dongzhaigang to Lianjiang of Leizhou Peninsula,Shenzhen Bay,Chenghai of eastern Guangdong Province and Jiulongjiang Estuary of Fujian Province and grew well.Since 1998,S.apetala has been extensively used in mangrove restoration in China.With its rapid growth and quick expansion of planting area,some disputes on S.apetala introduction have emerged in recent years,such as whether it competes with indigenous species for resource and habitat,whether it will become an invasive species,and whether it should be restricted or widely used in mangrove planting programs.In order to explore these questions,studies of S.apetala introduction since late 1980s were reviewed within four aspects,namely:(1) environmental adaptability,changes of physiological characteristics and genetic diversity among communities of different introduction locations;(2) silviculture techniques,including planting,seedling and sapling nursing techniques,post-planting management;(3) stand productivity,including biomass accumulation,litterfall production and nutrient elements absorption;and(4) ecological effects,including protective effect,environmental purification,ecological control,impacts on indigenous mangrove species,and possibility of biological invasion.We concluded that(1) S.apetala grows well in intertidal zones of thick and soft muddy soil with low salinity(0—15‰) in China′s south coasts,and can be used as pioneer species in mangrove afforestation due to its fast-growth,high adaptability and stress resistance,but will threaten the growth of indigenous mangrove species if it is introduced to native mangrove communities or planted densely with indigenous species;(2) there are obvious effects of ecological protection,environmental purification and control over Spartina alterniflora for S.apetala forest;(3) the natural spread speed of S.apetala is slow due to the restraint of salinity,light intensity,temperature,soil and tide,and no significant impacts on the structure,functions or biodiversity of native mangrove cummunities are found,so whether S.apetala will be an invasive species cannot be determined at present;(4) with the enhancement of environmental adaptability of S.apetala,its ecological effects might change,and one should be cautious with further expansion of the plantation before its adverse ecological impacts are clear.We suggest that it should be planted mainly on low tidal beaches where native mangrove species cannot grow.Finally,we put forward some important fields for future research,including(1) monitoring of ecological influences of S.apetala on indigenous mangrove communities and the trend of biological invasion;(2) impacts of S.apetala on coastal aquatic animals;(3) planting patterns of mixed forest of S.apetala and indigenous mangrove species,considering species diversity,self-sustainability,comprehensive ecological effects and landscape,and then further research into impacts of S.apetala on indigenous mangrove species under these patterns;and(4) economic utilization of S.apetala. |
