Nitrogen Storage Of Three Typical Forest Ecosystems In Hainan Island

The variation and control of nitrogen storage in forest ecosystem are critical for studying the carbon and nitrogen biogeochemical cycle and its potential feedbacks to climate change. The study results could provides scientific basis data in forest ecological quality evaluation, nutrient cycling, cultivation of fast-growing and high-yield plantations, and nature forest protection.This paper take rubber plantations in Sanya, Danzhou, Tunchang, Wenchang and natural forests in different recovery processes in Diaoluo Mountain as research objects, separately discuss their nitrogen storage in diferent forest ecology system.At the same time, the paper studies and compares the nitrogen storage in various types of young forest, middle age forest, mature forest, the whole ecosystem and each part of them. The result are as follows:1.Nitrogen storage in rubber plantations in Hainan Island is between7.89to12.19t/hm2, meanwhile the nitrogen storage in10years since cut forest is the lowest when that in30years forest is the highest. Nitrogen storage in rubber plantations is7.49-11.26t/hm2, which consists91.7%-97.8%of the whole ecosystem. Nitrogen storage in arbor layer are heaviely effected by biomass. And its age and nitrogen storage becomes bigger when biomass increase, which changes between0.13-0.92t/hm2. Nitrogen storage in vegetation layer under canopy is between0.019to0.053t/hm2. Nitrogen storage in litter layer is between0.043and0.062t/hm2.2.Nitrogen storage of eucalyptus plantations ecosystem is between10.60t/hm2to12.25t/hm2, and the nitrogen storage in ecosystem increases with age increase. Nitrogen storage in soil layer is97.5%-99.0%of the entire ecosystem. The nitrogen storage of arbor layer changes between0.013t/hm2to0.226t/hm2of which contribution rate is only0.1%-1.8%in nitrogen storage of entire ecosystem. The variation range of nitrogen storage of the herb layer is0.067to0.074t/hm2.The nitrogen storage of litter layer range0.031-0.038t/hm2.3.Nitrogen storage of natural forest in is between12.00t/hm2-18.83t/hm2. Nitrogen storage in natural forest ecosystem is the highest. And the shorter time of recovery, the less nitrogen storage in natural forest. It’s nitrogen storage of soil layer is10.90-17.24t/hm2. The soil contribution rate of natural forest to nitrogen storage of ecosystem is90.8%-92.5%. Nitrogen storage in arbor layer in natural forest is0.68-1.19t/hm2. Nitrogen storage in layer under arbor is0.07-0.10t/hm2. Nitrogen storage in litter layer is between0.12to0.31t/hm2.4. Dividing forests into three types: young forest, middle age forest and mature forest is closer to the actual growing of forests, so it can show difference in nitrogen storage and distribution pattern between different types of forests.(1) Nitrogen storage in mature natural forest, which is16.02t/hm2, is the highest among three divisions when that in young rubber plantations is the lowest, which is6.7t/hm2. Only natural mature forest reached the estimated Chinese forest ecosystems average nitrogen storage. Distribution of nitrogen is not same in different types and different age classes’, soil layers are main nitrogen storage body in the three types of forest ecosystem;(2) Natural forest’s nitrogen storage and biomass is higher than rubber plantations, rubber plantations is higher than Eucalyptus plantations, the reason is because of the tree features and cropping patterns. Nitrogen storage in under arbor layer and litter layer:natural forest> eucalyptus plantations> rubber plantations, it is because of the pattern and species management characteristics and sampling time;(3) In each age class the rubber plantations has the lowest soil nitrogen storage, eucalyptus plantation soil nitrogen is higher than natural forest in the middle age. Except mature natural forest systems(14.69t/hm2), the other three types of forest system nitrogen storage did not reach the national average (13.2t/hm2) and tropical rainforest, tropical seasonal average (13.64t/hm2);(4) Natural mature forest and young rubber plantations forest ecosystems are more fragile, should strengthen the protection and reduce human interference;(5) The current Hainan island rubber plantation, eucalyptus plantation and natural forest have a certain potential to fixation nitrogen, the plantation has the high potential. Extend the life of rubber tapping, change the current six-year eucalyptus plantation rotations, training large diameter class timber eucalyptus plantation and strengthen the protection of natural forests, prevent human interference can effectively enhance nitrogen fixation and carbon sequestration capacity of forest ecosystem, at the same time it can also enhance the service function of forest ecosystems.