The Characteristics Of Coarse Wood Debrisin Picea Likiangensis Var. Linzhiensis Forest

Coarse woody debris（CWD）is the material formed after the death of trees in forest ecosystem,including Logs,Snags,Large branch and Stumps.CWD is an important structural and functional component of ecosystem,and its dynamic change law is influenced by many factors such as tree species,mortality and decomposition rate,and its reserve characteristics are the basis for studying the overall change law of CWD.Picea likiangensis var.Linzhiensis is one of the main tree species of subalpine dark coniferous forest in Tibet Plateau.It has the characteristics of wide distribution,large area and high stability,plays an important role in constructing plateau ecological barrier and maintaining ecological environment.In this study,the 1 hm²original Picea likiangensis var.Linzhiensis forest in Bomigang Nature Reserve was taken as the research object.The decomposition level,reserves,types,nutrients,forest regeneration and spatial distribution of CWD in Picea likiangensis var.Linzhiensis forest in southeast Tibet were studied,and the carbon pool and nutrient characteristics of CWD in high altitude cold temperate forest ecosystem were systematically studied.Draw the following conclusions:（1）Picea likiangensis var.linzhiensis is the dominant tree species in the standard plot of Picea likiangensis var.linzhiensis forest with the highest density.The density,volume and reserves of CWD in the forest are 191 plants·hm^-2,261.97·m³hm^-2and 80.72 t·hm^-2,respectively.The order of total diameter reserves of coarse woody debris is:large diameter（61.25%）>medium diameter（28.55%）>small diameter（10.20%）.The density of CWD with different input modes in Picea likiangensis var.linzhiensis forest is negatively correlated with the increase of diameter class,which is a typical inverted“J”structure and the contribution rate of Logs is the highest.The decomposition levels of all CWD and Logs in Picea likiangensis var.linzhiensis forest are generally approximately normal distribution,and the decomposition levels ofⅡandⅢare mostly;Dead tree concentrationⅠ,Ⅱ,decomposition level;The number of big branches and Logs is small,which are concentrated in a lower decomposition level.In terms of reserves,CWD in Picea likiangensis var.linzhiensis forest is generally in a moderate decomposition state withⅡandⅢdecomposition grades as the main ones.（2）The large CWD storage base in Picea likiangensis var.linzhiensis forest makes the CWD carbon storage relatively high,reaching 39.88 t hm^-2,About95.75%,of which the carbon storage of Logs is as high as 38.18 t hm^-2,which is the main contributor to forest carbon pool.CWD carbon storage accounts for the most in the initial stage of decomposition,mainly concentrated in decomposition grades II(15.39 t hm^-2)and III(16.54 t hm^-2).The general performance of different types of coarse wood residues is Logs>Snags>stump>branch.The nutrient content of different decomposition levels is carbon>calcium>nitrogen>potassium>magnesium>phosphorus.The nutrient reserves of coarse wood residues with different decomposition levels and different input methods vary with the change of CWD reserves.Among them,the carbon content increases significantly with the increase of decomposition level,which has great potential for carbon storage,and the nitrogen concentration increases significantly with the increase of decomposition degree,indicating that coarse wood residues may be an important long-term nitrogen source.The contents of other nutrient elements（phosphorus,potassium,calcium and magnesium）are relatively stable.（3）The effect of CWD on seedling regeneration is closely related to its decomposition level,existing form and habitat.There are 1222 regenerated seedlings in 1 hm²plot,including 841 seedlings,165 young trees and 216 small trees,and the number of regenerated seedlings of Picea likiangensis var.linzhiensis is the largest.The regenerated seedlings on CWD showed a downward trend with the increase of decomposition grade,and mainly concentrated on grade III;The number of medium and small diameter seedlings（0～45 cm）is relatively high,and the number of seedlings on the ground is lower than CWD,which shows that the density of updated seedlings gradually decreases with the increase of seedling height.（4）With the increase of spatial scale,CWD of different types,diameter classes and decomposition levels in Picea likiangensis var.linzhiensis forest shows cluster distribution,and a large number of studies show that aggregate distribution is the stable distribution pattern of most natural populations.In addition to Logs,different forms of existence also mainly show cluster distribution.Except that the decomposition levels ofⅡandⅢfluctuate between cluster distribution and random distribution with the increase of scale,each decomposition level is clustered distribution.CWD of smaller diameter class（10～30 cm）fluctuates in cluster distribution and random distribution with the increase of scale,and all other diameter classes show cluster distribution.Through the above research results,it is helpful to improve the CWD research of different climatic zones and different forest ecosystems in China,and supplement the distribution law of coarse wood residues in alpine regions and their nutrient pool data in forest ecosystems.Using the internationally unified classification standard of CWD to classify the CWD of spruce forest in Linzhi is conducive to comparing the results on a global scale,integrating and perfecting the global data of rough wood residues,and providing basic data for fully understanding the key ecological processes such as material cycle related to rough wood residues in the forest regeneration process of forest ecosystems in Tibet.