起测径对南盘江流域次生林中枯立木空间结构的影响

Influence of Minimum Measured Diameter on Spatial Structures of Snags of Secondary Forests in the Nanpan River Basin

树木大小是林分的基础属性,反映个体在森林生态系统过程中扮演的角色和地位。作者于2016-2018年在中国西南地区南盘江流域松栎混交林中建立3块永久性标准固定样地(A、B、C),并用双相关函数g(r)、标记相关函数kmm(r)、标记变差函数γ(r)和k-邻体距离分布函数Dk(r)分析不同大小枯立木的空间结构特征,以揭示林分水平上枯立木的大小和空间结构之间的关系。结果显示:(1)枯立木的起测径(minimum measured diameter,mmd)越小,小尺度上(r=0~5 m)的分布格局趋向聚集状态,但随着起测径的增大(mmd=5~8 cm),随机分布格局几乎占据每个尺度(r=0~20 m)。(2)当起测径等于1~2 cm时,枯立木的大小在小尺度上(r=0~1 m)接近聚集分布,除此之外它一直保持随机分布。(3)当起测径≤4 cm时,枯立木的树种分布集中;反之,它在每个尺度上越接近或成为随机状态。(4)当起测径由1 cm增大至8 cm时,r=0~10 m之内相邻木的株数减少且距离增加,其变化程度受到林分株数的影响。研究表明,枯立木的起测径与其分布格局类型、标记特征以及距离分布紧密相关,暗示同种小树易呈团块死亡,而大径的枯立木偏向随机分布;对比分析枯死木的空间结构需使用统一的起测径标准。

Tree size is a fundamental attribute of forest stand,reflecting the role and status of individuals in the process of forest ecosystem.We established three permanently fixed plots(A,B and C)in a mixed forest of pine-oak in the Nanpan River basin,southwestern China in 2016-2018.We analyzed the spatial structures of snags of different tree size using pair correlation function g(r),mark correlation function kmm(r),mark variogram functionγ(r),and distance distribution function kth neighbor Dk(r),with the purpose to disclose their relationships at stand level.Our results showed that:(1)distribution pattern tended to be clumped at small scale(r=0-5 m)when the minimum measured diameter(mmd)of snags was small.Random distribution pattern,however,dominated the majority of scales(r=0-20 m)with the increasing of minimum measured diameter(mmd=5-8 cm).(2)Tree size approximated aggregation at small scale(r=0-1 m)when the minimum measured diameter was equal to 1-2 cm.Otherwise,it maintained a random pattern.(3)Tree species showed a clump pattern when the minimum measured diameter was smaller than 4 cm.On the contrary,it was in or became random at each scale.(4)The abundance of neighbors decreased and the distances between any pair increased within r=0-10 m with the increasing of the minimum measured diameter from 1 cm to 8 cm.These results suggest that the minimum measured diameter of snags is closely related to distribution pattern,tree mark and distance,implying the small-sized snags of conspecific have a clump pattern while the large-sized ones are likely to be distributed randomly.A uniform minimum measured diameter of snags should be used when analyzing spatial structure.