基于结构方程模型的林分上下层间结构与树木多样性耦合关系研究

Coupling relationship of structure and tree diversity between upper and lower canopy layer based on structural equation model

为探讨林分上下层间结构与树木多样性的关系,以阿什河流域天然次生杂木林为对象,构建了立地条件-林分上层结构-林分上层树木多样性-林分下层结构与树木多样性的结构方程模型。结果表明:立地条件(ξ1)对林分上层结构(ξ2)具有直接正影响,影响系数为0.59;对林分上层树木多样性(ξ3)具有正影响,总影响系数为0.75,直接影响系数为0.43;对林分下层结构与树木多样性(ξ4)具有负影响,总影响系数为-0.58,直接影响系数为-0.12。林分上层结构(ξ2)对林分上层树木多样性(ξ3)具有直接正影响,影响系数为0.55;对林分下层结构与树木多样性(ξ4)具有负影响,总影响系数为-0.55,直接影响系数为-0.38。林分上层树木多样性(ξ3)对林分下层结构与树木多样性(ξ4)具有直接负影响,影响系数为-0.31。对林分下层密度(x11)影响最大的林分上层观测变量为林分上层树冠面积(x7),总影响系数为-0.19,直接影响系数为-0.12。对林分下层平均树高(x12)影响最大的林分上层观测变量为林分上层平均树高(x6),总影响系数为-0.28,直接影响系数为-0.13。林分上层树冠面积(x7)和树高多样性(x10)对林分下层树种多样性(x14)影响较大,影响系数分别为-0.38和-0.36。树冠面积(x7)的影响全为直接影响;树高多样性(x10)的直接影响大于间接影响;林分上层结构(ξ2)与树木多样性(ξ3)中的观测变量对林分下层树冠面积(x13)影响不明显。

In order to clarify the relationship of structure and tree diversity between upper and lower canopy layers,we built the structural equation model of the site condition- structure of upper canopy layer- tree diversity of upper canopy layer- structure and tree diversity of lower canopy layer based on the secondary multiple species forest beside the Ashi River in southern Heilongjiang Province. The results showed that site condition（ ξ1） had a positive impact on structure（ ξ2） and tree diversity（ ξ3） of the upper canopy layer with the total path coefficients of 0. 59 and 0. 75,and the direct path coefficients of 0. 59 and 0. 43,respectively. Site condition（ ξ1） had a negative impact on structure and tree diversity of the lower canopy layer（ ξ4） with the total path coefficients of- 0. 58,and the direct path coefficient of- 0. 12. Structure of the upper canopy layer（ ξ2） had a positive impact on tree diversity of the upper canopy layer（ ξ3） and a negative impact on structure and tree diversity of the lower canopy layer（ ξ4）,with the total path coefficients of 0. 55 and- 0. 55,and the direct path coefficient of 0. 55 and- 0. 38,respectively. Trees diversity of upper canopy layer（ ξ3） had a directly negative impact on structure and tree diversity of the lower canopy layer（ ξ4）,with the path coefficient of- 0. 31. Of all the observation variables of structure and tree diversity for the upper canopy layer,canopy area（ x7） was the most important factor affecting density of the lower canopy layer（ x11）,with the total path coefficient of- 0. 19 and the direct path coefficient of- 0. 12. Average height（ x6） was the most important factor affecting average height of the lower canopy layer（ x12）,with the total path coefficient of- 0. 28 and the direct path coefficient of- 0. 13. Canopy area（ x7） and height diversity（ x10） were the most important factors affecting tree species diversity of the lower canopy layer（ x14）,with the total path coefficients of- 0. 38 and- 0. 36,respectively. The impact of structure（ ξ2） and tree diversity（ ξ3） of the upper canopy layer on the canopy area of the lower canopy layer（ x13） was not obvious.