Basical Quality And Environmental Effects Of Fallen Logs In Tsuga Longibracteata Forest In Tianbaoyan National Nature Reserve

Tsuga longibracteata W. C. Cheng, a rare and endangered coniferous species endemic to China,plays an important role in promoting forest succession,maintaining the balance and stability offorest ecosystems, and water conservation. However, barren site condition and poor naturalregeneration were critical problem for the protection and restoration of Tsuga longibracteata forest.Fallen logs play important roles in maintaining the structural and functional integrity of forestecosystems;they provide habitat for forest species, act as a long-term nutrient store, and contributeto nutrient cycling,energy flow, regeneration succession and soil formation. These functionsprovide evidence for the importance of logs for forest ecosystem. A better knowledge of logs couldhelp in solving the problem of stability and regeneration in Tsuga longibracteata forest. Base onthe investigation on fallen logs quantity and quality,nutrient stock,energy stock and environmentalfactors（including topographic factors, human disturbance, stand structure, meteorological factors andsoil microenvironment under fallen logs）were track monitoring, the present study try to demonstratethe logs ecological function in nutrient cycling and energy flow,and found the right site for seedbedstudy.It also contribute to a reference basis for conservation and sustainable management of Tsugalongibracteata forest. The results showed that:（1） The fallen logs in Tsuga longibracteata forest in Tianbaoyan National Nature Reserve,mainly belonged to slightly decayed and small-classed logs,that is,they mainly distributed at therange of decay class I~II, diameter class0~10cm, length class1~3m.Logs density were decreasedwhile volume increased with the increased of diameter class（length class）, Logs density, volumeand covered area were increased with the decreased of elevation.Logs density were decreased withthe increased of decay class, volume and covered area distribution were close to normal distribution.fallen logs quantity and quality were differed significantly among decay class and forest types （P<0.05）. fallen logs volume in this area was18.14m~3/hm~2, and the selective volume was only3.37m~3/hm~2when we chose class IV for seedbed study.（2） The content of C, K were not significantly in different decay classes（P>0.05）, whileN, P and C/N were extremely significantly（P<0.01）; With the increased of the decayclass, thecontent of N, P displayed the increased trend, however C/N decreased; logs nutrient stocks inhighly decay class were larger than slightly decayed; and the total C stock was2.316t/hm~2,while N stock was9.832kg/hm~2,P stock was1.154kg/hm~2,K stock was1.713kg/hm~2. Nutrient stocks waslowest in Tsuga longibracteata pure forest, and largest in Tsuga longibracteata+Phyllostachysedulis forest, C stock in different forest types showed the following trend: Tsuga longibracteatapure forest <Tsuga longibracteata+hardwood <Rhododendron simiarum+Tsuga longibracteata <Tsuga longibracteata+Phyllostachys heterocycla pubescens, and N,P,K stocks followed Tsugalongibracteata pure forest <Rhododendron simiarum+Tsuga longibracteata <Tsugalongibracteata+hardwood <Tsuga longibracteata+Phyllostachys heterocycla pubescens, the fournutrient stocks decreased during the decay process,but the release stock was lower, which indicatedthat nutrients return was slow for the slow decomposition of fallen logs,they played an importantrole in maintaining forest stability and sustainable development.It is especially more important forthe rare and endangered species Tsuga longibracteata in barren site condition.（3）Burnable logs index and burnable entropy results showed that fallen logs combustibility weredecreased with the increased of decay class, logs in Tsuga longibracteata pure forest were thelowest combustibility and potential energy, whereas highest in Tsuga longibracteata+Phyllostachysedulis forest; in this area,logs were low combustibility and had lower ignition potential,so in theforest management,retain but not remove the current logs could optimize meet their function.（4） Soil properties under fallen logs were analyzed by variance analysis,correlationanalysis,path analysis and factor analysis,the results showed that soil bulk density and pH werelower, while porosity, SOC, TN, TK, protease, urease, invertase, cellulose and acid phosphataseactivity were higher in soil beneath fallen logs, which indicated that fallen logs were contributed toimprove the soil productivity; SOC were increased with the increased of decay class, SOC wereextremely significant difference in soils under fallen logs of all decay classes, while the other soilproperties were no significant difference; season were significant effects on most soil properties（P<0.05）; Soil properties showed a significant correlation between each other, Highly significantcorrelation was found between SOC and the selected physical and chemical properties,while thesame between TN and the five soil enzyme activities. SOC,TN and C/N were the most importantindex on the five soil enzyme activities.Comprehensively, fallen logs was contributed to improvesoil quality, and promote nutrient cycling and energy flow in soil environment.（5） Redundancy analysis（RDA） were performed to determine therelationships between fallenlogs and environmental factors, and the results showed that fallen logs quantity and quality was strongly effected by elevation, precipitation have the lowest effect on the release of C,N and Pstock. Except for human disturbance, fallen logs were not mainly from self-thinning and senescence,but mostly origin from snow or wind disturbance.The highly decayed logs, soil enzymeactivities,nutrient and energy release stock were increased from northern to southern slope, whichindicated that elevated temperature will accelerate the decomposition of fallen logs in the studyarea, and thus shorten the duration of its function as a seedbed, so sampling logs that use forseeding experiment should not be overly concentrated on southern slopes in further study. Slopegradient had the least effect on logs quantity and quality and soil enzyme activity under fallenlogs,but middle effect on nutrient and energy release,seedbed logs were found on middleslope,biodiversity was richer on class Ⅳ, which were advantage for seedlings colonization.Thus,all the results suggested that fallen logs on Tsuga longibracteata forest floor acted aslong-term storage for nutrients,contributed to soil fertility and heterogeneity, the accumulation oflogs would lead to accelerated nutrient cycling and energy flow,which would promoted the stabilityof forest ecosystem.In addition, if the class Ⅳwas chooseen for seedbed experiment, they shouldput in middle slope,and without considering slope gradient, but not be overly concentrated onsouthern slope.