小兴安岭针叶林冠层对雪水量平衡的影响机制

The effects of forest properties on snow processes is very important for hydroecology in seasonal snow cover regions, but the mechanism of forest canopy to snow processes is unrevealed in Xiaoxing'an mountains. Canopy properties of spruce-fir-Korean pine forest, larix gmelini plantation and snow processes are surveyed on the basis of the sample positioning plot experimental data of Tangwang river basin at long term. Cut-tree experiments, weighing lysimeters and meteorological instruments are used to measure canopy snow migration and meteorological factors. And the continuous observations of snow accumulation and melting dynamics are based on the experiment of regular snow-depth and snow-density from the plot to the stand scale. However, the study is rare on the effects of multi-scale field and modeling of forest canopies and meteorological factors on snow migration processes. Therefore, we apply this project to study the effect mentioned above. This project is to more deeply analyze the effect of forest canopy on snow water equivalent balance during the complete accumulation and melting period within Xiaoxing'an mountain range as follow: 1. The interaction to processes of snow interception will be studied among canopy structures and intercepted snow migrations and meteorological factors. 2. The mechanisms of intercepted snow migrations will be explored throughout the snow season. （1 and 2 support application in canopy hydrology models, processes of snow interception and removal of intercepted snow by sublimation, melt-water drip and mass release are simulated by building snow physical model.） 3. Site-scale canopy structure measures will provide a reliable basis to explain the spatial variability of within-stand snow deposition.Hydrological effect of canopy structures and meteorological factors on seasonal evolution of snowpack will be studied within stands as well（1,2 and 3 will be used to construct the model of snow water equivalent balance）. This research will provide data and scientific guidelines for forest management practices that are in agreement with the optimization of water resources.

本项目以小兴安岭汤旺河流域典型的云冷杉红松林和落叶松人工林为研究对象，基于样方尺度和林分尺度，通过样地定位调查、气象因子观测、切割树称重技术和应用改进型称重式蒸渗仪，对降雪运移过程和林内雪变化过程进行了研究。探析林冠层对降雪截留过程的影响机理，阐明冠层雪的运移规律，解析林内雪演变过程和空间分布的驱动机制，构建基于物理过程的冠层雪水文模型和针叶林雪水量平衡模型，揭示森林冠层对雪水量平衡的作用机制，为寒区森林生态系统经营和流域水资源优化管理提供数据支撑和科学依据。

在中国东北高寒区，森林覆盖率高达40%，季节性积雪储量高于青藏高原地区，年积雪量可达50～90 mm，占年降水量的1/9～1/10。而森林冠层截留降雪的再分配作用深刻影响森林内积雪的空间分布，森林冠层界面与大气界面的能量和物质的强烈交换也显著改变森林内积雪和融雪的过程，因此深入开展森林冠层对雪水量平衡影响机制的研究，是东北高寒区森林水文生态雪需要填补的薄弱环节。本研究选取位于伊春市五营区黑龙江省丰林国家级自然保护区内的原始红松林分布区为研究区，对研究区内的森林冠层的截留降雪过程和林内的积雪及融雪过程进行了系统的研究，建立了林冠截留降雪模型和林内最大积雪量与林冠参数的统计模型以及积雪期林内雪水量模型。. 研究结果显示：1）在积雪期林外最大雪深和最大雪水量都要高于红松林的，且林外样地的最大雪深和最大雪水量与高郁闭度红松林相比，差异均显著。在融雪期，林外的融雪速率最高，高郁闭度红松林的融雪速率最小，但方差分析表明林外与红松林间的融雪速率无显著性差异。在积雪后期和融雪后期，雪密度随着温度的升高而增加。在积雪初期和融雪期间的雪水量的变异性较高，红松林由于林冠层郁闭的作用导致林内积雪分布不均匀，其雪水量的变异性均要高于林外的。2）森林冠层对雪分布的影响显著，郁闭度最高的样点的雪水量与郁闭度最低的样点相比最高差异超过50%，且在积雪期和融雪期二者之间的雪水量差异均极显著。积雪期的最大雪水量和林冠开度、林冠间隙度呈显著正相关，与有效叶面积指数以及坡度呈显著负相关。郁闭度较高林分的雪水量变异性要高于林间空地的。3）林冠截留雪量与林外降雪量和有效叶面积指数以及树高呈显著正相关，与林冠开度和林冠间隙度呈极显著负相关。林冠截留降雪量与林外降雪量的关系符合幂函数拟合模型。. 本研究揭示了森林冠层对雪水量平衡的影响机制，研究将为流域水资源优化管理以及林分尺度至流域尺度的森林雪水文模型的建立提供数据支撑和科学依据。