The Productivity And Nutrient Cycling Of The Mixed Forest Of Chinese Fir And Castanopsis Fissa

Abstract:Chinese fir is an important fast-growing, high yield timber species in South China, which has been planted largely since 1950s, then forest area increased year after year. That led to forest decline in productivity and soil fertility decline. Currently planted fir plantation with the decline in the productivity of soil degradation has been cause great concern, has become a hot topic in forest science. The mixed forest rich in biodiversity with strong resistance, stability and other characteristics of ecosystems, and create a mixed forest to improve site conditions, can play better benefits and protection against natural disasters, is an effective way to overcome the decline of soil nutrient. C. fissa is adaptable, easy-propagation, fast-growth, its seeds and root system have a stronger force, lush foliage, large leaves, which is an excellent mixed tree for Chinese fir. In this project, the growth, biomass, litter product, and nutrient cycling of the mixed were investigated in two 16 years old forests. This researches are to explore the mixed forest ecosystem productivity and nutrient cycling characteristics rules, to provide a theoretical basis and practical guidance for the management of mixed forests. The main results were as follows:1. The mixed and fir plantations' DBH, tree height, individual volume, the timber volume are both present the same rule in the different slope:down slope> middle slope> upper slope. In this study, the pure forest of Chinese fir are more productive than the mixed. the pure forest's average height, average DBH, individual volume were greater than the mixed. Generally speaking, the pure forest in the timber volume and growing stock were higher than mixed. The annual diameter growth shows that the two stand's diameter growth both increased at first and then decreased, but the mixed down faster.2. There are significant differences in total biomass between the Chinese fir pure forest and the mixed forest. The total biomass of the mixed in middle slope and lower slope are respectively higher than the pure plantation by 31.14%,5.51%.The same stand biomass in different slope are arranged in the order:upper slope>middle slop>lower slope. Mixed forest litter layer biomass was significantly higher than pure plantation, in the upper, middle and down slope by 5.16 times, 2.99 times and 1.75 times. The mixed forest was significantly increased biomass. 3. There were no significant differences of nutrient concentration in various organs in the two different stand. Leaves of N, P, K concentration are the highest, but the law of the other organs of nutrient concentration was not obvious; N, P, K concentration in shrub and herbage were higher than understory coverage.4. The nutrient accumulation between the Chinese fir pure forest and the mixed forest are quite different. In the uphill, mixed and pure forest N, P, K nutrient accumulation reflected as follows:fir plantations> mixed forest, in addition to in the downhill slope and the middle slope, except P but the other is:mixed> fir forest. The nutrient accumulation shows the rules that N> K> P, slope> middle slope> upper slope.In the understory vegetation, litter nutrient accumulation was maximum. The N, P element accumulation of the litter shows the mixed>>the Chinese fir plantations, but except the lower slope's phosphorus accumulation.5. The difference of nutrient using efficiency of tree layer between the Chinese fir plantations and the mixed forests are evident. Uphill, tree layer nutrient using efficiency as follows:mixed> pure plantation, in the middle slope, the two stand have similar nutrient use efficiency, but in the downhill showing that pure plantation> Mixed.6. In terms of annual litter production, mixed forest in each slope were 1.23t/hm2,1.55 t/hm2,3.31t/hm2,are respectively 3.24 times,1.3 times,2.98 times more than the Chinese fir plantations'. Create a mixed fir C. fissa stands significantly increased the amount of litter, but in mixed stands, the litters of C. fissa are in the ascendant.7. There were obvious different in retention of nutrient elements between the Chinese fir plantations and the mixed forest. Retention of nutrient elements of mixed in the middle slope, downslope respectively higher than the pure plantations' by 28.16%,19.39%; The nutrient return of the mixed forest are higher than the Chinese fir plantations in each slope. The annual nutrient uptake of the mixed are 1.29 times,1.49 times than the fir plantations in middle and lower slope. Compared with P and K, the intensity of the cycle of N is the strongest. The total nutrient cycling capability in mixed are best in the downhill.