| For nearly 30 years,Sonneratia apetala is planted in large area of coastal beach in China.The S.apetala was introduced into Jiulong River Estuary in 1997.It quickly adapted to the growing environment in Fujian Province and was introduced to other areas.As the exotic mangrove plant introduces from abroad to China,many scholars worry about its invasiveness.This research uses a method which combines the field investigation and indoor experiment,to study the biological characteristics,introduction of history,distribution and population characteristics of typical samples and the effects of S.apetala on the major epifauna under the forest.It provides scientific data for evaluating the ecological impact of S.apetala in Fujian Province and also provides theoretical basis for the protection and ecological construction of mangrove in China in the future,especially for the work of artificial mangrove construction under difficult site conditions.The results of this study are as follows:(1)The fruiting time of the S.apetala in Fujian Province is twice a year.Autumn fruits begin to have buds in March,flourish and flowering in April and fruiting in May.From July to September,the fruits are mature and plentiful.From October to November,it is the end of fruit ripening and the number of fruit decrease.Spring fruits begin to bud in early November,bloom in December,and then bear fruit,which last until March of the following year.During this period,the amount of fruits are low,the fruits are small,and they fall basically immature.It is fruitless in April.(2)In Fujian Province,there are 77.0±7.9 seeds in a mature fruit,the 1000-seed weight is 42.06±0.05 g.Under indoor culture conditions,the germination rate is 94.80±5.21%,the germination index is 60.45±2.78,and the vigor index is 23.90±4.30.Annual yield of seed rain is 10491.95 ind·m-2.Only in April,there are no seed rain.The seed banks are investigated in five habitats:S.apetala+Kandelia obovata forest,S.apetala+K.obovata forest margin,K.obovata forest,mixed forest and light beaches.It is found that the seed banks of S.apetala+K.obovata forest have the largest amount and the number of seeds stored in most soil layers in the remaining 4 habitats are less than 1000 ind·m-2.The overall seed germination rate,germination index and vigor index of seed bank in each soil layer of the 5 habitats are low.(3)The annual output of litterfall of S.apetala is 1476.19 g·m-2(from February in 2019 to January in 2020).The annual yield of litterfall in four organs accounts for annual litter output is shown as fallen leaves(52.06%)>fallen fruit(32.88%)>fallen branches(13.21%)>fallen flowers(1.84%).The fallen leaves periods and fallen flowers periods are mainly concentrated in summer,and the fallen branches periods and fallen fruit periods are mainly concentrated in autumn.(4)Based on information and surveys,since it was introduced successfully to the Jiulong River estuary in Fujian Province in 1997,S.apetala has been planted in many bay beaches.While S.apetala did not survive in such as Ningde City.At present,there are 4 urban areas(Zhangzhou City,Xiamen City,Quanzhou City and Putian City)in Fujian Province where there is S.apetala distribution and growth.In Xiamen City,there are no phenomenon of natural regeneration and growth of S.apetala,while natural growth of S.apetala appeared in Zhangzhou City and other places with low salinity.No S.apetala spreads into dense native mangrove plant communities and it mainly grows on the plain,Sparlina alterniflora grasslands and the forest margin of the mangrove community.In the protected area,if it is necessary to clear the S.apetala that has spread to the periphery of the protected area,it can be removed by means of regular cutting.Native plants such as K.obovata can grow naturally in the S.apetala forest.Under appropriate conditions in wild,S.apetala can naturally regenerate in S.alerniflora grassland.(5)In the mangrove community of Haicang Bay,located on the first floor of the tree is the S.apetala with a density of 1.33 ind·50 m-2 and an average height of 8.50±0.58 m;The mangrove plants on the second floor of the arbor are arranged in order of average height from high to low,followed by S.apetala,K.obovata and Rhizophora stylosa.The mangrove plants located in the shrub+sapling layer are in the order of average height from the highest to the lowest,namely,K.obovata,R.stylosa and Avicennia marina.(6)The S.apetala community in Tong' an Bay,Xiamen City,the lodging phenomenon and the lodging degree of S.apetala is more serious than that of K.obovata.However,in the community of K.obovata+S.apetala,the lodging degree of the S.apetala is smaller.In the mangrove community of Jimei Bay,Xiamen City,two years after the typhoon struck,the proportion of S.apetala population size in normal growth and treetop semi-withered S.apetala size is smaller than that in normal growth and treetop semi-withered K obovata population size.However,the proportion of the population size of the S.apetala that is completely dead at the top of the tree is 9.23%more than that of the population size of the K.obovata that is completely dead at the top of the tree.(7)The number of the major epifauna species in S.apetala+K.obovata forest,S.apetala+K.obovata forest margin,K.obovata forest,mixed forest,light beaches and artificial groove is 21,11,8,6,9 and 6,respectively.There are 8 dominant species in S.apetala+K.obovata forest.In addition,habitat with more dominant species is the K.obovata forest and S.apetala+K.obovata forest margin.The Margalef index and Shannon-Wiener index in S.apetala+K.obovata forest are the largest,while the artificial channels and light beaches are smaller.The Pielou index of the K.obovata forest and the S.apetala+K.obovata forest are larger,while the artificial grooves and light beaches are smaller.In the light beaches and artificial groove,the value of Simpson index is relatively large,while the value of Simpson index in the S.apetala+K.obovata forest and K.obovata forest is relatively small.The results show that there is no biological invasion after introducing S.apetala into Fujian Province.In Fujian Province,the time of blossoming and bearing fruit of S.apetala is advanced,the fruiting period is increased,the seed quality is good,the seed rain,seed bank and litterfall are large.However,seed germination only occurs under suitable conditions,and because it is a strong positive plant,the diffusion growth of seedlings only occurs in habitats such as forest margins,light beaches and S.alterniflora grasslands,and does not invade the native mangrove plant community,which will not inhibit the growth of other mangrove plants,but create favorable conditions for the natural colonization and growth of other mangrove plants.If it is necessary to remove the S.apetala that has spread to unsuitable areas,it can be removed by regular felling.The S.apetala has a strong competitive effect on the growth of S.alterniflora.Because of its tall tree shape and its location at the highest level of the community,S.apetala is more vulnerable to damage during typhoon weather in coastal areas,and its ecological recovery capacity is less than that of K.obovata.In the wind and wave environment,the adaptability of S.apetala is less than that of K.obovata.The so-called "invasion" feature of S.apetala is not as powerful as expected.The diversity of the major epifauna under the S.apetala forest is higher than that in other habitats.Adopting the planting mode of "introduced species+native species ",can increase the species diversity of the community,each mangrove species occupies its niche,promotes the growth of native mangrove plants and seedlings of native mangrove plants.This planting pattern makes mangrove plants play different coordinating and complementary roles in landscape collocation and protection.Therefore,the ecological impact of S.apetala in Fujian Province is more beneficial than unfavorable.Rational utilization of S.apetala in Fujian Province can not only increase mangrove resources and mangrove area,but also produce good ecological benefits.However,as an alien introduced plant,it is necessary to conduct long-term monitoring of the status and dynamics of S.apetala,so as to obtain more current situation and dynamic data,regulate the species timely,under the premise of ensuring the safety and scientific of introducing exotic species,they should be reasonably used. |
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