Study On The Gap Disturbance Mechanism Of Picea Schrenkiana-Dryopteris Filix-mas Stand

Forest system is always in a constantly mutative state owing to the double effects of self-development and exoteric influence. In this dynamic system, disturbance acting as the main driving factor of spatio-temporal pattern change, drives forest cycle. And forest forms mosaic structure because of disturbance. The structure not only enhances heterogeneity of forest, but also changes validity of resources, maintains the dynamic stability of forest. Therefore, mastering adequately the disturbance regime is extremely important for the sustainable forest development. The thesis takes Picea schrenkiana-Dryopteris filix-max original forest in the Western Tianshan National Nature Reserve as research objects,adopting the method of whole stand in temporary plot, regarding natural disturbance of gaps,coarse woody debris(CWD) and regeneration responses to gaps as an union,focuses on the study about the characteristics of gap disturbance,CWD dynamics and regeneration on fallen wood.The results are as follow:In 1 hm2 temporary plot in the Western Tianshan National Nature Reserve,the population structure of Picea schrenkiana-Dryopteris filix-mas pure stands is stable,the patterns of age,diameter and the height of Picea schrenkiana-Dryopteris filix-mas pure stands are all in inverse J-shaped curves,indicating a typical uneven-aged stand structure.The age distribution shows that Picea schrenkiana-Dryopteris filix-mas pure stand is in a continuous regeneration and saplings are very abundant in their self-regenerating process. Analysis about CWD indicates that a five-class decay classification system of fallen wood is developed,and the decomposition time of each class is 4a,18a,38a,68a and 92a,respectively.Under the nature condition,the decomposition time that the woody debris density decreases 50%,90% and 95% is approximately 59a,196a and 255a,respectively.Meanwhile,the research estimates the volume and the biomass of CWD in Picea schrenkiana-Dryopteris filix-mas pure stands.Mean CWD volume is 337.61m3/hm2,and dry biomass is 87.98Mg/hm2.Based on the woody debris density,there is a simple negative exponential relation between time and density,and it can be expresses by y=0.435e-0.01174t(R2=0.9386).What is more,the measurements of nutrient content show that the average percent of C,N,P,K and Na is 55.93%,0.34%,0.12%,0.06%,0.03%,the average content of Ca and Mg is 56.74g/kg,34.89g/kg, respectively. At the same time, the same nutrient among different decomposition classes is different but inconspicuous.Through field investigation of gaps,there are 17 gaps in the study region.The return interval of gap disturbance is 763a.Most of gaps are formed by many gaps makers,and most of gaps are formed in 60～80a.Shape of all gaps various,shape index of most expanded gaps and canopy gaps are seldom close to 1.The sizes of expanded gaps range from 20 to 280 m2,the sizes of canopy gaps vary from 0 to 180 m2.Furthermore,in Western Tianshan National Nature Reserve,there are many seedling and sapling growing on the fallen wood.Through the research of regeneration of fallen wood,the results indicate that the average orientation of all fallen woods is northwestern,and the average orientation of fallen woods having regeneration is northeastern.Regeneration on fallen wood is not strongly influented by the orientation of fallen woods,but markedly affected by decomposition.