Effects Of Dwarf Bamboo (Fargesia Denudata) Density On Its Biomass And Community Growth Beneath Subalpine Forest Of Western Sichuan

Dwarf bamboo (Fargesia denudata), a staple food bamboo for the giant panda, is the dominant synusia of the forest ecosystem in Wanglang National Nature Reserve, which plays an important role in forest ecosystem structure and function. As yet there is lack of information on the effects of the bamboo density on the biomass and community growth although there have been many reports on forest regeneration driven by bamboo, bamboo regeneration, and bamboo population dynamics. The influences of bamboo density on the biomass and its distribution dynamics, nutrient stock, nutrient accumulation, nutrient distribution pattern, nutrient retranslocation and characteristics of nutrient biocycling, therefore, were studied by setting up three bamboo communities with different densities beneath a bamboo-fir (Picea purpurea) forest over a growing period (from May to October 2003). Considering the complex effects of biotic and abiotic factors on bamboo growth, the plots were chosen according to the criteria with similar slope, direction, soil parent material and texture, tree canopy, etc, which is the prerequisite to realize the objectives here. The results here showed that, 1) The above-ground biomass of three communities increased continuously in the growing period, and its production increased with increasing stem density, but the rate decreased. In the growing period, the below-ground biomass played a process as gained in the beginning of the growing period, and declined, and then gained in the end of the growing period. But the below-ground biomass of the community with lower stem density (D2 and D3) declined later than higer stem density community. The percent of bamboo components biomass in total biomass was different with different stem density and different growth time during the growing period. 2) At the end of bamboo growing period, 2003, the total biomass of the bamboo communities was 11.77±0.62 kg.m-2 for D1, 6.41±0.19 kg.m-2 for D2, and 3.55±0.35 kg.m-2 for D3, respectively; and the average stem biomass in the three communities was 53.49g for D1, 45.78g for D2, 44.43 for D3. The average production of three bamboo communities was 3.22 kg.m-2 for D1, 1.19 kg.m-2 for D2, 0.71 kg.m-2 for D3 over a growing period, 2003. The majority of community production lies on growth of the bamboo with litter than 14 age classes and, the most of others stop growth. 3) The relationships between leaf and below-ground components biomss, between above-and below-ground biomass in the bamboo communities was also regulated by the stem density, and the correlation coefficient increased with increasing stem density. The bamboo branch and leaf biomass distribution in culm height was significant variety in three bamboo communities with different stem density. The ratio of branch or leaf biomass to total biomass was decreased with increasing stem density under 0 ~ 150 cm culm height in bamboo community however; above 150 cm culm height was oppsite. And the effects of bamboo density on culm and above-ground biomass distribution in different culm height was no significant variation. 4) All the total, above-and below-ground nutrient stocks increased with increasing stem density, and the order of nutrient stocks was K>N>Ca>P>Mg. The total accumulation quantity in bamboo community over one growing period could put in the order of K>N>Ca>P>Mg. Furthermore, the total and above-ground nutrient accumulation quantity increased with increasing stem density, the accumulation ratio order was similar in different communities, and it was Mg>Ca>P>N>K, the bamboo community with highest density (D1) had the highest accumulation ratio. The ratio of nutrient storages in below-ground system (root and rhizome) decreased with increasing stem density but; the ratio of nutrient storages in above-ground system (leaf, branch and stem) increased with increasing stem density. 5) Over the growing period, 2003, the litterfall production of three bamboo communities increased with increasing stem density. The concentrations of C, N, P and K in litters decreased with increasing stem density, but Ca and Mg reversed. It was founded that N, P, and K concentrations were lower in litters than in fresh leaves, increased from May to July, and decreased after July in growing period. The potential retranslocation capacity of P was strongly regulated by stem density, but N and K not by stem density. And the potential retranslocation capacity of N, P and K showed the ranked orders as K> N> P. The retranslocation of C in bamboo was not significant in three bamboo communities. The accumulation of Ca in litter increased with increasingstem density. The accumulation of Mg in litter increased with increasing stem density, but the retranslocation capacity decreased with increasing stem density. 6) The nutrient elements absorption quantity in three bamboo communities increased with increasing stem density over the growing period, and put in the order of K>N>Ca>P>Mg. The return nutrient by litterfall also increased with increasing stem density and. A part of P input into bamboo community system by leaching, the quantity increased with increasing stem density. The utilization coefficient of nutrient elements was between 0.19 and 0.51 in three bamboo communities, and the community with higher stem density had higher utilization coefficient. The nutrient elements cycling coefficient decreased with increasing stem density, among the nutrient elements, Ca and Mg had the higher cycling coefficient, and P had the lower cycling coefficient. The nutrient elements recycling period in the bamboo community increased with increasing stem density.