Attributes And Effect Factors Of Coarse Woody Debris In Picea Schrenkiana Forests Of Tianshan Mountains

Coarse woody debris(CWD)is generally considered to be the general term for dead woody objects with a diameter of?10 cm in the forest,plays important structural and biogeochemical roles in Tianshan Picea schrenkiana forest ecosystem processes,which profoundly affects nutrient cycling,carbon storage and hydrological ecological processes in forest ecosystems.In addition,it also plays an important role in maintaining forest biodiversity and forest regeneration.Explaining its storage characteristics is the basis for studying CWD.However,on a large-scale no studies have yet been reported in this area,and the previous studies on the scale of the sample can not avoid the influence and limitation of the spatial sampling scale on the research results.The definition specification of CWD formulated by USDA Forest Service and LTER defines wood debris with a big head diameter?10cm as coarse wood debris(CWD).The specific types of CWD are specified by Harmon and Sexton(1996):Snags are the wood debris with inclination rate(deviation from the vertical direction)<45°,big head diameter?10 cm,height?1 m.Height<1m,but other features similar to snags are judged as stumps.Based on the combination of field investigation,laboratory test and data analysis,study objectives of this report were to examine storage estimate by composition,diameter and decay class distributions,and analyze spatial pattern and other basic characteristics of CWD in P.schrenkiana forest of Tianshan Mountains.On this basis,the effect factors of CWD storage are discussed.Results indicate that:(1)A substantial number(936)of CWD(?10cm diameter)exists in 8 hm~2P.schrenkiana forest dynamics plot,snags,logs and stumps are the main forms of CWD.P.schrenkiana is the single component species of CWD in the dynamics plot.Density,volume and storage of CWD in this plot averaged 117 N/hm~2,15.13 m~3/hm~2and 4.52 t/hm~2,well below the global average of coniferous forest CWD storage,but at the lower end of the range of coniferous forest storage in China.Stumps have the highest density by accounting for 41.03%of the total CWD.Logs were the main contributor and accounted for 45.41%and 52.21%of the total CWD volume and storage,while the percentage of snags and stumps were 20.58%and 27.21%.Density and storage of snags were the lowest by composition,which accounted only about 20%of the total CWD storage.(2)We found that CWD quantity in P.schrenkiana forest by diameter class was followed the inverse J-shaped,which decreased sharply with the increase of the diameter grade.The diameter distribution of this population is highly skewed towards smaller-sized(?30cm dia.)CWD,which accounted for 83%of total CWD quantity.The storage of different types of CWD in the sample plot was different in the diameter distribution,but it generally expressed as a"U"structure,which increased after an initial decrease.The storage order of CWD by diameter is small diameter grade(55.6%)>large diameter grade(25%)>medium diameter grade(19.4%).(3)In the sample plot,snags and logs are mainly at the mid-low decomposition level,while stumps are concentrated at decay class III,IV,and V.However,there was no obvious distribution rule of logs.The distribution of total CWD by decay class is skewed toward decay class?and?.Overall,the current decay class distribution of CWD in P.schrenkiana forest appears to follow a natural progression of CWD decay.Our results also showed that the CWD diameter in the plot has a certain influence on the distribution of decay class.With the increase of the diameter,the degree of CWD decomposition continues to increase.(4)The CWD spatial clustering intensity of different types,different diameter levels and different decomposition levels in P.schrenkiana forest overall decrease with the increase of scale,showing a distribution pattern of small scale clustering distribution and large scale random distribution.(5)The formation of CWD storage and distribution characteristics of Tianshan P.schrenkiana forest is affected by various factors such as its own characteristics,natural environment,human disturbance history and forest development stage.Among many environmental factors,stand density,canopy density and elevation are the main factors affecting the storage characteristics of CWD in P.schrenkiana forest of Tianshan Mountains,while soil factors and other factors explain the storage characteristics of CWD to a lower degree.This study quantified the storage of CWD in P.schrenkiana forest of Tianshan Mountains on a large scale,analyzed the distribution characteristics of CWD and its influencing factors,which can provide a scientific evidence for the sustainable development and management of P.schrenkiana forest,and could be useful in developing ecologically sustainable forest management guidelines.