子午岭次生油松林立木竞争格局研究

Competition Pattern of Standing Trees in Secondary Pinus Forest in the Ziwuling Mountains,China

研究干旱区森林立木竞争及空间分布格局,旨在为揭示干旱区森林恢复演替过程中竞争动态和格局形成驱动机制提供科学依据。经全面调查之后,依据时空互代原理选择了4个处于不同演替阶段,面积为0.25 hm2的大样地进行研究。采用Hegyi邻体密度模型研究立木竞争强度指数。采用Kriging法与Hegyi法相结合研究立木竞争的空间格局。采用一元和二元O-ring函数模型分别研究了乔木空间分布格局和乔木种间空间相关性。结果表明:在上述4个群落中油松(Pinus tabuliformis)种群密度分别为1476、996、800、648株·hm^(-2),白桦(Betula platyphylla)种群密度为48、32、44、16株·hm^(-2),山杨(Populus davidiana)种群密度分别为64、28、24、12株·hm^(-2)。3种主要乔木的竞争指数由高到低依次为油松、白桦、山杨,各物种竞争指数均随演替阶段的增长而下降;演替后期,胸径2~15 cm油松个体减少明显,而胸径大于30 cm的个体数量有所增加;在所有演替阶段中,油松竞争指数均随着胸径的增加而下降;油松种群竞争空间格局为典型的非匀质斑块状格局。点格局分析结果表明,油松种群在0~5 m尺度呈现聚集分布,且与其他树种在5~15 m尺度存在空间负相关。本研究主要结论如下,黄土高原次生油松林群落中油松竞争指数高于其他物种。油松在各演替阶段均呈现出基于径级大小的竞争不对称性,演替后期油松群落自疏机制为限制小径级个体的生长。竞争的格局在水平空间尺度具有斑块性,随着演替的进行,高竞争斑块在数量、范围和强度上减小,但并不会消失。油松生态策略为小尺度聚集分布,与其他树种在5~15 m尺度空间负相关,这个尺度已经超过了经典的树冠竞争理论范畴,其背后的原因需要更加深入地研究。

In order to reveal the driving mechanism of competition dynamics and pattern formation in the process of arid forest restoration and succession,the competition and spatial distribution pattern of standing trees in arid forest China were studied,and a typical secondary Pinus tabuliformis forests was investigated in the Ziwuling Mountains,China,and four larger sample sites(0.25 hm^(2) each)in different developmental stages were selected,according to the method using space instead of time,and some details of population,size,inter-tree competitions and spatial pattern of four sample sites were acquired respectively.The results showed that,in the four communities at different stages of succession,population densities of P.tabulaeformis were 1476,996,800 and 648 per ha^(2) respectively;population densities of Betula platyphylla were 48,32,44 and 16 per ha^(2) respectively;and population densities of Populus davidiana were 64,28,24 and 12 per ha^(2) respectively.Competition index of main tree specials decreased with succession,and showed P.tabulaeformis>B.platyphylla>P.davidiana.Quantity of small individuals(diameter at breast height from 2-15 cm)decreased obviously;but quantity of large individuals(diameter at breast height larger than 30 cm)increased.In all succession stages,the competitive intensity of P.tabulaeformis decreased with the increase of diameter.The horizontal spatial competition pattern of P.tabulaeformis showed a patchiness distribution.P.tabulaeformis clumped at the scales 0-5 m,and negative correlated with other tress specials at the scales 5-15 m.Quantity of small size Pinus individuals decreased obvious in later developmental stage.Inter-tree competition of P.tabulaeformis was stronger than other tree species,and inter-tree competition decreased in the later developmental stage.The conclusions are as follows:the size of trees are negatively correlated with the competition index;the competition index of P.tabulaeformis is higher than other species;the competition at community scales decline as development,and the quantity and range of the patches with an intense competition decline,but do not disappear yet.Competition and spatial relations are observed within the scales of 5-15 m which are larger than the average crown size of Pinus.The conditions suggest that the range of inter-tree influence could expand indirectly beyond their crown range through unknown methods,which should be further investigated.