Study On Litterfall Of Two Major Forest Stands In Maoershan Area

Populus davidiana Dode. and Fraxinus mandshurica Rupr. are two important natural secondary tree species in Northeast China. Both Populus davidiana and Fraxinus mandshurica have high economic value, ecological value and social value. Especially Fraxinus mandshurica is an important rare timber tree species in Northeast China. There were no detailed studies on litter and forest floor of Populus davidiana and Fraxinus mandshurica in this region. The research had been carried out in two important natural secondary forests of P. davidiana and F. mandshurica, Laoshan station of Maoer mountain Forest Park of Northeast Forestry University, Shangzhi, Heilongjiang province during May 2003 to April 2006. From aspects of amount, components, seasonal dynamics of litter, litter decomposition, the characteristic of nutrient element release during decomposition of litter and forest floor had been investigated.The results indicated:1.During the three years, the annual litterfall of F. mandshurica stand was 4538.3 kg·hm-2·yr-1, which was 11% higher than P. davidiana stand(4076.2kg·hm-2·yr-1). Leaf litter was the most important component of litterfall, and it accounted for 84.6% and 75.6% of total litterfall in P. davidiana and F. mandshurica, respectively. The monthly variety of P. davidiana and F. mandshurica showed one apexes, peaked in September and October annually. 2.The Weightlessness ratio of leaf litter of P. davidiana, P. davidiana mixture, F. mandshurica and F. mandshurica mixture were 49.79%, 63.11%, 59.54% and 63.40% percent after two years, respectively.The time of 50% decomposition of leaf litter of P. davidiana, P. davidiana mixture, F. mandshurica and F. mandshurica mixture were 1.59a, 1.36a, 0.86a and 0.90a respectively, and the time of 95% decomposition were 6.63a, 5.64a, 3.72a and 3.96a, respectively.3.The quantities of microbes (bacteria, actinomyces, fungi) were different during different period in two forests soil surface layer of the two forests. Bacteria was the dominant microbes in May and July, next was Actinomyces, Fungi was the least microbes. In September Actinomyces was the dominant microbes, next was Bacteria, Fungi also was the least microbes. 4.The maximum enzyme activities of Catalase in two forests occurred in July. The maximum enzyme activities of invertase and urease in P. davidiana forests occurred in May. The maximum enzyme activities of invertase and urease in F. mandshurica forests occurred in July and May respectively. The maximum enzyme activities of proteinase in P. davidiana forests occurred in September and in F. mandshurica forests occurred in May.5. The result shows that total content of 6 major nutrient elements after two years decreased 23.30% in P. davidiana leaf litter, P. davidiana mixture decreased 33.37%, F. mandshuricaleaf litter decreased 32.84%, F. mandshurica mixture decreased 37.60%. As to the average concentration of the 6 major nutrient elements in four leaf litter, the order has no changed after two years. Releasing rate of 6 major nutrient elements was different during different period in four leaf litter, but four leaf litter were releasing.6. The storage amount of the un-decomposing and sub-decomposing layers were analyzed by investigating the remnant litter under the forest. The result shows that F. mandshurica forest only had sub-decomposing layer, storage amount was 13 5Q0 kg-hm"2. The total remnant storage amount was 39 33.4 kg-hm"2 in P. davidiana forest. To some extend, it reflects the facts that the litter has the ecological function of containing rainfall and balancing the water in ecosystem because the total water-holding amount and the average water-holding rate are so high that they reached 5.55t-hm"2 and 139.5% in P. davidiana forest, 2.233t-hm"2 and 165.4% in F. mandshurica forest, respectively. The quantities of microbes (bacteria, actinomyces, fungi) and the activities of enzymes (such as proteinase, invertase, catalase, polyphenoloxidase and so on) in the forest floor were different in different layer. The order of elements was in sequence of N > P > K > Ca > Mg in the P. davidiana forest, but N > P > Ca > K > Mg in the F. mandshurica forest.