Dynamics Of Litter Production, Nutrient Return And The Relationship Between Litter And Soil Fauna In Eucalyptus Grandis

Litter is major material pool of forest organic and the base of maintain the soil nutrient, and the major course of the material cycling and energy flow in forest ecosystem. It is very important for the nutrient to return to soil through litter to remain the sustainable productivity of the forest. Now, the Eucalyptus plantation is one of most tree species planted in south of our country. It is vital significance to plant and manage the Eucalyptus plantation through research the characteristic of litter to thoroughly understand the structure and the function of the forest ecosystem. From July 2004,the experiment choose the Eucalyptus grandis plantation planted in 1997 in HongYa SiChuan province, study on the litter production, nutrient return, nutrient retranslocation, litter decomposition and the soil nutrient change in a growth cycle, the result showed:(1) The annual of 2004.7-2005.6 litter production for four Eucalyptus grandis plantation were 8786 kg/hm²,8112 kg/hm²,5590 kg/hm²,6011 kg/hm². 2005.7-2006.6 litter production for four Eucalyptus grandis plantation werel0398 kg/hm² , 10258 kg/hm², 5916 kg/hm², 7012 kg/hm², respectively, it was increase 16.2%, 7.1%, 5.5%, 14.3% .The annual litter production was connected with the forest density, leaf production was increased with the increase of the standing density, branches and barks had no remarkable relation with the density. The components of litter production was leaf> branches > barks. There was a peak and valley in the whole year, highest in May and lowest in January. The litter production of seasonal variation tendency in sequence of spring > summer > autumn > winter. Leaf mainly fell in spring while branches and barks fell main in summer.(2) The annual five macro-elements return to the soil through litter were 109.833 kg.hm²,104.95 kg.hm², 71.81 kg.hm², 75.34 kg.hm², respectively, it was increase 13.2%, 17.2%, 5.7%, 11.9%, the sequence of nutrient return was N > K > Ca > Mg > P.The nutrient return was higher in spring and summer than in autumn and winter, lowest in January.(3)Before falling, most of N, P in leaf and branches were transferred physiologically, while K, Ca, Mg transferred direction was uncertain, sometimes was positive and sometimes was negative, 2005.7-2007.6 was positive. The transfer efficiency of P was the highest, reached 58.9% in leaf and67.2% in branches average each month. Ca was the lowest in the transfer efficiency, 8.3% in leaf and 11.5% in branches.Mg was reached 19.6 % in leaf and 21.8%.The nutrient retranslocation of leaf and branches before amount falling was highest, the nutrient internal recycling was extremely obvious. The annual nutrient retranslocation were 145.96, 118.10, 70.72, 78.26 kg/hm² respectively, in sequence of E₁ > E₂ > E₄ > E₃, so the nutrient retranslocation was being connected with the forest density. The nutrient retranslocation in leaf was several times as in branches. The nutrient retranslocation in leaf was in sequence of N>K>Ca>P> Mg, but in branches was not the same, E₁ was K > N > Mg > Ca > P, E₂ and E₃ were N > K > Ca > Mg > P, E₄ wasN>Ca>K>Mg>P。(4) From yearly variation of the soil nutrient, at present the soil organic, entire N, effective P, the rapid effective K content decreased in varying degree compared to 2006. Because interfere of the local people take the litter for firewood.The experimental Eucalyptus grandis plantation in HongYa had already achieved the quantity mature age. In order to compensates the nutrient the Eucalyptus grandis growth absorbed in the soil as far as possible, the ecology cut season should to be supposed after the branches and leaves massively falling, the autumn and winter will be suitable, this can partially return the nutrient absorption of Eucalyptus grandis land. As the short rotation plantation , bough was the Eucalyptus grandis mainly cut and use, there were 78.70 -81.74% nutrient reserve return to the forest land if fallen leaf,branches,barks and root keep in the forest land, this will be advantageous to the formation of self- nutrient circulation mechanism and maintenance forest land nutrient balance, in order to realize the Eucalyptus grandis plantation sustainable management. As the converting lands into forests project and the frail ecosystem restores specie for development in the low massif mausoleum area of south Sichuan province, the Eucalyptus grandis has the good society, economic and ecologic benefit.