The Productivity And Nutrient Cycling Of The Mixed Forest Of Chinese Fir And Mytilaria Laosensis

Chinese fir is one of the rapid growing species in the south of china, with the advantages of fast growth, good material, high yield and widely cultivated area etc. However, with the increasing area of Chinese fir plantation, land capability and stability of stand of pure Chinese fir forestry significantly declined, so that the output diminished generationally in Chinese fir plantations. How to keep continued productivity and stability of the forestry production of Chinese fir plantation has become the major subject to resolve, while to build mixed forestry with Chinese fir forests is considered to be one of the methods to maintain long-term productivity of Chinese fir plantation. M. laosensis has straight form and good quality, which is a fine tree for soil and water conservation, soil improvement, afforestation and biological fireproof. This thesis compared the Chinese fir plantations and the mixed forest of Chinese fir and M. laosensis, it synthetically analyzed biomass, productivity and nutrient cycling to explore the features and regularity of the mixed forest ecosystem productivity and nutrient cycling. It provided the theory basis and practical experience for the evaluation of Chinese fir plantation to the sustainable management. The main results were as follows:1. There was great difference between the growth of the Chinese fir plantations and the mixed forest. The difference of DBH growth manifested as that of Chinese fir had obvious advantage in middle slope of the mixed forest, but it showed greater advantage in lower slope of the Chinese fir plantations. The growth of trees height in upper slope, middle slope and lower slope of the mixed forest was increased by 14.1%,19.0% and 9.1% respectively compared with that of the Chinese fir plantations. The volume was 132.87m3/hm2,191.83m3/hm2 and 267.48 m3/hm2 respectively, it improved 21.3% and 17.3% in upper slope and middle slope, which showed that there was great superiority in the upper slope and middle slope of the mixed forest. Compared with the same stand in the different slope positions, each index of the two stand were showed:lower slope>middle slope>upper slope.2. There was significant difference between the biomass of the Chinese fir plantations and the mixed forest. The total biomass of the mixed forest in the same slope position was higher than that in the Chinese fir plantations; The total biomass in the different slope positions of different stands showed that biomass of the lower slope was the highest, and the second was in the middle slope, while the third was in the upper slope. The distribution of the different organs' biomass in upper slope and middle slope of the mixed forest was:stem>root> branch> skin> leaves, but biomass in lower slope was that:stem>root>branch>leaves> skin. The distribution of the different organs' biomass in different slope positions of the Chinese fir plantations was that stem was the highest and the difference among the root, branch, skin and leaves was not obvious.3. The difference of N, P, K accumulated amount between Chinese fir plantations and the mixed forest showed that N accumulated amount in upper slope, middle slope and lower slope of the mixed forest was increased by 104.4%,93.4% and 12.7%, respectively, compared with that in the Chinese fir plantations under the growth condition of the same slope. P accumulated amount was increased by 53.1%,37.7% and 59.6%, respectively. K accumulated amount was 42.0% and 99.5%, respectively higher than that of the Chinese fir plantations. The total nutrient accumulation in the different slope positions of the same stand was that:lower slope>middle slope>upper slope, this variation was similar to the nutrient accumulation of tree layer in different stands.4. The difference of nutrient using efficiency between Chinese fir plantations and the mixed forest was evident. The nutrient use efficiency of tree layer in upper slope, middle slope and lower slope of the mixed forest was increased by 11.5%,9.5% and 57.0%,respectively, compared with that of the Chinese fir plantations and the nutrient use efficiency was increased by 40.8%,-13.0% and 33.0% respectively compared with that of Chinese fir plantations. Under the condition of different slope positions, the nutrient use efficiency of tree layer of mixed forestry was arranged in the order:upper slope>lower slope>middle slope, while nutrient use efficiency of pure Chinese fir was that:upper slope>middle slope>lower slope.5. The difference of litter's annual output between Chinese fir plantations and the mixed forest was evident. The litter's annual output in the same slope positions of different stands was:the mixed forest>the Chinese fir plantations. The litter's annual output in different slope positions of the same stand was showed that:lower slope>middle slope>upper slope. The composition of litter of the mixed forest was:branch> leaves>fruit>flower in upper slope, compared with that leaves>branch>fruit>flower in lower slope and middle slope, while it showed:branch>leaves>fruit>flower in Chinese fir plantations.6. The difference of the nutrient's remaining quantity, annually retained, annually uptake and return proportion between Chinese fir plantations and the mixed forest was all arranged in the order:the mixed forest>the Chinese fir plantations. The nutrient cycling ability in middle slope of the mixed forest had a distinct advantage over that of the Chinese fir plantations. The nutrient's remaining quantity and annually uptake of N was all highest in the same slope position of the same stand, and the lowest was P. The highest of annually retained and return proportion was N, and the minimum was K. The nutrient's return proportion of the Chinese fir plantations was arranged in the order:middle slope>lower slope>upper slope, it could be seen that the soil condition in the middle slope of mixed forest was in favor of the nutrient's circulation.In short, compared with the Chinese fir plantations, mixed Chinese fir forestry with M. laosensis was in favor of the growth of Chinese fir. The average tree height, average DBH, volume of timber and volume of the mixed forest were all higher than that of the Chinese fir plantations. And the biomass, nutrient accumulation, nutrient using efficiency and the nutrient's return proportion all showed the same rule. It showed that a mixed forest had higher productivity and nutrient cycling ability than that of Chinese fir plantations.