| Forest is the most important component of the terrestrial ecosystem,and tropical rain forest is the forest ecosystem with the the most rich species composition,the most complex community structure and the greatest role in maintaining human living environment among all forest types.At present,many large forest dynamics monitoring plot have been established all over the world.Many theories have been developed to explain the species coexistence mechanisms in forest communities by studying the species composition and structure of various forest types around the world in detail.According to the species number,structure and distribution,the species in the community can be classfied into different groups.Although different species groups have different contributions to the community,their effects on the community can’t be ignored.Legumes are often regarded as one of the important component of the community because of their biological nitrogen fix nitrogen abilities.In the text,the researches about species composition,structure and dynamics of forest communities,and the ecological functions of leguminous plants were summarized.In order to understand the species composition,structure and dynamic changes of woody plants in the tropical forest,all trees in one 60 hm~2 plot were censused in 2012 and 2018 and spatial analysis were applied.Dominant species,rare species,key species were then analyzed in 2012 and 2018.Finally,we calculated neighboring abundance,richness biomass,survival rates and growth rates of seven leguminous trees in the plot and discuss their effects on neighboring non-leguminous trees.The main results are as follows:(1)In general,the species composition of the Jianfengling(JFL)60 hm~2 plot was stable.From 2012 to 2018,the species changed from 62 families,155 genera,290 species to 69 families,154 genera,291 species,with 3species disappeared and 4new species occurred.The DBH distribution of the plants in the JFL 60 hm~2 plot showed an obvious inverted"J"shape,and most individuals were in the 1-5 cm diameter class.The average DBH increased from 9.87 cm to 10.22cm.The species with the largest importance value is Livistona saribus,and the importance value changed from 3.57 to 3.68.Between 2012 and 2018,63513 individuals died and 38610 new individuals grew in the JFL 60 hm~2plot,with the total number of stems decreased from 439615to 412912.(2)The dominant species in JFL 60 hm~2 plot are Livistona saribus,Gironniera subaequalis and Cryptocarya chinensis,with DBH varied from 20 to 35 cm,0 to 25 cm,and 0 to 11 cm.Their abundance decreased and their average DBH increased.The rare species in the JFL 60 hm~2 plot are Murraya paniculata,Ilex hainanensis and Engelhardia spicata.Abundance of Murraya paniculata and Engelhardia spicata decreased,but their average DBH increased.Abundance of Ilex hainanensis increased but their average DBH decreased.All Murraya paniculata and Engelhardia spicata are small individuals,but some of Ilex hainanensis have large individuals.There are seven key leguminous tree species in the JFL 60 hm~2 plot.All of them have nitrogen fixation abilities.The size and structure of these leguminous tree are stable,most of their them with DBH between 0 and 5 cm.The annual mortality rates and recruitment rates of dominant species,rare species and key species are less than 5%.Spatial distribution patterns of the dead and recruitment individuals are similar with their original population.Populations with large abundance showed aggregated distribution patterns in the small scale,but showed random or evenly distribution in the larger scale.(3)Key leguminous tree species have different effects on the neighboring plants:Relative neighboring abundance and richness of Ormosia semicastrata,Archidendron clypearia and A.lucidum are higher than those of non-leguminous trees both in 2013 and 2018.Relative neighboring abundance and richness of other four leguminous are lower than those of non-leguminous trees.For neighboring survival rates,O.semicastrata,O.fordiana,and A.clypearia are higher than those of non-leguminous trees.The relative biomass of the neighbors of O.semicastrate,A.lucidum and A.clypearia are greater than that of non-leguminous tree,and the relative biomass of the O.blansae and A.utile are less than that of non-leguminous species.The relative biomass of the neighbors of O.xylocarpa is greater than that of non-leguminous tree in the small distance and less in the large distance.The relative growth rates of the neighbors of O.semicastrata and A.clypearia are less than those of non-leguminous tree,while others are greater than those of non-leguminous tree.The relative abundance,richness,biomass,survival rates and growth rates of the neighbors were stable in 2012 and 2018.There is a significant linear relationship between relative abundance and richness(P<0.01).There are also significant linear relationships between relative biomass and leaf nitrogen content,nitrogen fixation activities(P<0.001).On the whole,species composition,abundance and community structure in the JFL 60 hm~2plot are relatively stable.The species composition has obvious tropical characteristics,while most of stems are in small diameter class,and the plant density is high.The populations of dominant species,rare species and key species are stable.The impacts of different legume trees on neighboring plants are different,and the impacts of the same legume species on different community characteristics of neighboring trees are also different.The contents of soil nitrogen and phosphorus are the key factor affecting the leguminous trees’neighboring effects.The interactions among soil microorganisms,soil nitrogen and phosphorus contents maybe the key factors to explain how leguminous trees affecting their neighbors. |
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