The Effect Of Artificial Thinning Of Introduced Mangrove On The Growth And Recovery Of Native Mangrove

Futian Mangrove Nature Reserve,located in the central area of Shenzhen,is a mangrove natural reserve with the smallest area in China.This area plays important roles in producing organics,purifying air and water,providing habitat,etc.Sonneratia caseolaris and Sonneratia apetala which have been introduced from Hainan into this reserve in 1990s,have been growing rapidly,occupying a large area of the outer area of the beach,and gradually occupying the ecological niche of native mangrove in the nature reserve.In this study,Futian Mangrove Nature Reserve in Shenzhen city was taken as the object of study.The test field A and test field B were selected,then the test field A was kept as a control,and S.caseolaris and S.apetala in test field B were thinned in May 2014.Two years of comparative investigations of growth status of mangroves in both test field A and B were made in the October of the same year,and we researched the effects of mangrove on the growth and restoration of native mangroves by analyzing the growth status,quantity change,morphological index and community status of mangrove plants.The results included the following four main aspects.i:The growth of native mangroves by comparing the test field A and B shows that artificial thinning can promote the growth of native mangroves.In the early days of artificial thinning,the average plant height of Kandelia obovata and Aegiceras corniculatum were similar in test field A and B,and there was no significant difference in morphological index(P>0.05).But two years later,the plants height of K.obovata and A.corniculatum in test field B were 1.6 and 1.9 times of that of test field A respectively.The morphological indexes of K.obovata and A.corniculatum in test field B were significantly different from those in the untreated area(P<0.05).ii:Compared with the results of mangrove after artificial thinning,showed that thinning introduction mangrove was beneficial to increasing the number of native mangrove K.obovata and A.corniculatum.After two years of growth,the number of total mangrove plants in test field A and B were respectively 22 and 58 per 100 square meters.The number of adult K.obovata and A.corniculatum in test field B were 1.8,2.6 times of that of test field A and the number of seedlings were 2.6,2.3 times of that of test field A.iii:The effects of different coastal distance on the growth of mangroves showed that native mangroves,K.obovata and A cornicalatum,mainly distributed at 50?80 meter from the coastline,and introduced mangroves,S.caseolaris,distributed at 50?80 meter from the coastline.Therefore,the thinning of mangroves can be concentrated in the periphery of the beach;it will contribute to restore the ecological niche of native mangroves.iv:Artificial thinning is helpful to improve the diversity index,evenness and important value index of native mangrove species.From 50?110 meter of the coastline,the species diversity index of test field B was gradually increasing,while the untreated test field A drastically decreased from 70 meter of coastline.The species uniformity of test field B was increased with the time going,but for test field A,it did not change.The main value of K.obovata and A.corniculatum were respectively 2.0 and 2.0 times of that of test field B.Indicating that thinning of introduced species can promote the growth of native mangroves and increase their importance in the community.v:By comparing the growth rate of native mangroves and introduced mangrove trees after thinning,the growth rate of S.caseolaris in test field B was 7.1 times of K.obovata and 5.6 times of A.corniculatum respectively.The introduced mangrove S.caseoloaris growths rapidly,and still occupies the advantage,showing the risk of invasive species.If this situation has been there,it would cause that the mangrove structure is unstable and the resistance to external pressure is declining.Therefore,the thinning of mangrove species should be further strengthened.