| Woody debris consists of coarse woody debris (e.g. log, snag, stump and large branch), and fine woody debris (e.g. relics of wood, and branchlet), which are formed by died trees in the forest ecosystem. The former is an important structural and functional component, and plays crucial roles in significant pools of carbon and nutrients, maintaining biodiversity and forest regeneration in most of forest ecosystems. Meanwhile, woody debris especially fall and dead trees can often relate to the formation of forest gap and forest regeneration, resulting in different distribution patterns from forest gap center, gap edge to closed canopy. Compared with other forests, the alpine forest ecosystems above 3000-m altitude can be stronger limited by low temperature and natural disasters, leading to the forest regeneration can be more dependent on woody debris. But far less information has been available on woody debris storage and the distribution patterns as affected by forest gaps in the alpine forest. Therefore, a typical alpine forest Minjiang fir (Abies faxoniana) primary forest was selected in the eastern Tibet Plateau and western Sichuan. In order to provide with basic data for understanding the material cycling related to woody debris and forest regeneration in the alpine forest ecosystem, and scientific basis for sustainable forest management, therefore, the stocks of woody debris and their distribution characteristics from gap center to closed canopy, decomposition, and carbon and nutrient stocks were investigated in the alpine forest ecosystem.The aboveground biomass in the alpine forest ecosystem was 72.75 t/hm2, and woody debris was about 53.00 t/hm2. There was larger woody debris in closed canopy than that in forest gap and forest edge. Log showed the highest storage compared with other coarse woody debris, and stump storage accounted for less than 1% of total coarse woody debris storage. The woody debris with diameter> 40 cm accounted for 76.15%,74.55% and 75.68% of total woody debris storage from forest gap center, gap edge to closed canopy. No significant differences were observed in coarse woody debris with different diameters in forest gap center, gap edge and closed canopy. The storage of woody debris with Ⅲ and Ⅳ decay classes accounted for 50.02% in forest gap center,55.84% in gap edge and 62.90% in closed canopy, respectively. In addition, the proportion of log and stump storage was relatively lower in forest gap center compared with closed canopy and gap edge, but the proportion of snag and fine woody debris storage was relatively higher. Furthermore, the coarse woody debris storage with lower decay class was higher in forest gap center, while which with higher decay classes showed the significantly higher storage in closed canopy than those in forest gap center and gap edge.Substrate quality refers to the easy decomposition components (C. N. P) and difficult decomposition components (Lignin, Cellulose, Hemicellulose) combination, nutrient content, the proportion of each component, it’s the inner factor that effected woody debris decomposition. The concentration of N, P, lignin, C/N, N/P and lignin/N has been as an important indicator to measure the decomposition speed. With the decomposition of coarse woody debris, the content of C had no significant change in 511.07～604.86 g/kg, N and P content with the decomposition showed increasing tendency. N content of large branch with V decay class was higher than that in Ⅰ. Ⅱ and Ⅳ decay classes and stump with V decay class was higher than that in Ⅰ. Ⅱ and Ⅲdecay classes. P content of snag and stump with Ⅳ and V decay classes was significant higher than that in other decay classes, P content of log with Ⅰ decay class was higher than that in other decay classes, P content of large branch with Ⅰ decay class was higher than that in Ⅰ, Ⅱ and Ⅳ decay classes. The content of lignin with decomposition was first decreased and then increased between log and large branch. But the content of lignin with decomposition between snag and stump was gradually decreased. The change between lignin and cellulose was opposite. C/N and lignin/N showed similar tendency. C/N and lignin/N with decomposition was gradually decreased in log, snag and stump, C/N and lignin/N from Ⅰ to Ⅴ decay class was increased in large branch .In addition, four types of coarse woody debris N/P was decreased from Ⅰ to Ⅲ decay class and increased from Ⅳ to Ⅴ decay class.The ecosystem above ground in the alpine forest in Western Sichuan Province carbon, nitrogen, and phosphorus storage was 38.32 t/hm2,322.44 kg/hm2,157.95 kg/hm2. Coarse woody debris carbon, nitrogen, and phosphorus storage accounted for 70.44%,55.70%,5.48%. Metal elements content in different types of coarse woody debris did not show the same trends, but content were higher. According to the change of coarse woody debris density with time, nonlinear regression fitting curve was used to analysis coarse woody debris decomposition. The result showed log, correlation coefficient of large branch, snag and stump was 0.88,0.90,0.9 and 0.91. Decomposition rate of large branch, snag and stump was 0.105,0.114,0.097 and 0.127. Time of 95% decomposition was 28.53,26.28,30.8 and 23.59 years between four types coarse woody debris. Different type of coarse woody debris decomposition rate was different in the same conditions, it showed stump> large branch> log> snag.In summary, the alpine forest in Western Sichuan Province had a huge storage of woody debris, especially coarse woody debris storage and showed different distribution patterns from forest gap center, gap edge to closed canopy. Coarse woody debris carbon, nitrogen, and phosphorus storage was 26.99 t/hm2,179.59 kg/hm2 and 8.65 kg/hm2 in the alpine forest of Western Sichuan Province. Different type of coarse woody debris decomposition rate was different in the same conditions, it showed stump> large branch> log> snag. From above results, we provided the basic data for understanding the forest ecosystem in alpine forest of woody debris material circulation. |
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