Study On Litter Dynamics Of Abies Lanceolata Forest In Sejila Mountain

Forest litter is a product of plant metabolism in the forest,which is the main carrier of material and energy flow in the forest.It generally includes small branches,fallen leaves,bark,reproductive organs,animal debris,and resin debris.The Abies acutipennis（Abies Georgei var.Smithii）forest is the dominant population and top community in the subalpine region.It conserves water resources in the plateau area and the the Yarlung Zangbo River basin,reduces surface runoff in this area,increases soil fertility,and plays an important role in biodiversity and nutrient balance in the ecosystem of the plateau.Taking Sejila Mountain,a typical area in southeastern Tibet,as the research area,the forest litter was collected continuously on a monthly basis from different diameter classes of standing trees in a 1.0 hm²standard plot of a sharp pointed long braced fir primitive forest.Conduct research and analysis on the characteristics of litter composition,annual input,monthly dynamic changes,and nutrient cycling processes.The main conclusions are as follows:（1）From 2021 to 2022,in the sample plot of the sharp pointed long bracted fir forest in Sejila Mountain,the total litter amount for two years was 7.48T hm^-2year^-1,with an average annual litter amount of 3.74T hm^-2year^-1.The order of average litter size for different diameter classes of standing trees is:diameter class I>diameter class III>diameter class II>diameter class IV>diameter class V.The order of annual average litter size for the six components of litter is needle>branch>cone>bark>debris>male cone,and the order of litter size for each component of the five diameter classes of standing trees is consistent.Among them,the proportion of needle leaves to litter is 61.5%,followed by branches,accounting for 20.0%;The proportion of cones and bark is 12.8%and3.0%,respectively,and the proportion of litter from inflorescences and debris is about 2.0%.（2）The annual dynamics of litter in the sharp pointed long braced fir forest generally exhibit a bimodal curve.The peak period of litter is from October to November,with the highest proportion of litter being 28.72%in October;There will also be a small peak period in April,accounting for 11.34%;The litter volume in September is the lowest,accounting for only 3.7%.During peak and peak periods,the order of size for different diameter classes is consistent with the annual average litter volume for different diameter classes;In September,the size order of different diameter classes was different because diameter class III was greater than diameter class I.The monthly dynamic changes of leaf components also exhibit a bimodal pattern of size;There is no significant monthly dynamic change pattern in the litter of twigs,bark,and debris;The withering of cones and male cones varies in years of fruiting abundance and deficiency,and both exhibit a monthly dynamic pattern with a single peak.（3）The amount of litter in different directions of the standing tree crown is shown as follows:east>south>north>west,with significant differences in litter in different directions.The monthly dynamic changes of litter in different directions are consistent with the monthly dynamic changes of total litter volume.The order of litter volume in different directions of the crown of different diameter classes of standing trees also varies.（4）The content of C and N elements in fallen leaves is the highest in November.The average annual nutrient return of C element in the litter of the fast-growing fir forest is 1713.45 kg hm^-2a^-1,and the average annual total return of N,S,and P elements is 35.47 kg hm^-2a^-1.The average return amount of each component’s elements is in the order of C>N>S>P.The order of average annual returns of each component is:leaves>twigs>reproductive organs>debris>bark.In summary,among the components of the litter in the sharp pointed long braced fir forest,the leaf and branch components are the main components of the litter composition,and their dynamic changes can reflect the annual total amount of litter changes.Among the trees of different diameter levels,the first diameter level has the largest amount of litter.Based on the analysis of its crown area,it is believed that the litter amount of trees of different diameter levels per unit area of forest land is related to their crown area.The amount of canopy litter in different directions is related to the mountain orientation and the seasonal wind direction on the windward slope.