水曲柳阔叶混交林冠层光分布与天然更新相关性研究

探讨甘肃小陇山林区阔叶混交林冠层光分布对水曲柳天然更新的影响。以水曲柳为研究对象，采用大田试验和样地调查法，使用Hemi View数字植物冠层分析仪测定水曲柳阔叶混交林冠层的光照指标及LAI，建立DSF、ISF与LAI回归分析。结果表明，水曲柳在幼苗期适宜于在遮荫度<50%的环境下生长，当遮荫度>50%时，其苗高生长明显下降且与对照差异显著；水曲柳阔叶混交林中，林分冠层的郁闭度与叶面积指数（LAI）之间存在显著的正相关关系；散射光立地系数（ISF）、直射光立地系数（DSF）、散射光立地系数（GSF）、冠下总辐射（TotBe）随叶面积指数（LAI）的增大，呈明显的负相关关系，当郁闭度<0.66，散射光分布较多，更有利于水曲柳幼苗的生长与天然更新；对于种子扩散繁殖，距离母树0~5 m种子数量最多，随着距离的增加而减少，扩散半径因风向风不同而异，最远可达20 m。混交林冠层光分布对水曲柳幼苗期的天然更新有很大的影响。

Correlations between Light Distribution of the Crown Layer and Natural Regeneration of Fraxinus mandshurica

The objective of this study was to understand the effects of light distribution of broad-leaved mixed forest crown layer on the natural regeneration of Fraxinus mandshurica occurring in Xiaolongshan forest area,Gansu Province.Methods of general field investigation and sample plot observation were adopted.Hemi View Digital System was used to measure relative light indicators and light area index (LAI).The regression model between direct site factor (DSF) and LAI,indirect site factor (ISF)and LAI were built.The results showed that the optimal shade degree for the young seedling growth was less than 50%,when the shade degree was over 50%,the height growth significantly decreased,and presented significant difference with the control.In the broad-leaved mixed forest,significantly positive correlationship was observed between canopy density and LAI.Parameters such as ISF,DSF,GSF (general site factor),TotBe (total radiation below canopy) decreased with the increase of LAI,presenting significantly negative correlationship.When the canopy density was less than 0.66,the distribution of scattering light was more,which was beneficial to the seedling growth and natural regeneration of F.mandshurica.To the diffusion and reproductive of seed,there was more seeds in the distance about 0-5 m to the seed tree,and seed number decreased with distance,and the diffusion radius was different with the wind direction,the farthest distance was 20 meters.The results indicted that light distribution of crown layer in the broad-leaved mixed forest had significant effect on seedling natural regeneration of F.mandshurica.