Understory micrometorology across a larch forest density gradient in northeastern Siberia 2014-2020

Ecosystems affect the thermal dynamics of permafrost soils via impacts on the surface energy balance. Changes in vegetation structure and function therefore have the potential to modify the thermal characteristics of permafrost soils, with knock-on effects for soil carbon cycling. In Siberian boreal forests, stem density and canopy cover are influenced by wildfire severity. In this study we examine differences in understory air and soil micrometeorology at six stands, two high-density (greater than 75% canopy cover), two medium-density (25-50% canopy cover), and two low-density (less than 25% canopy cover), all within a single fire perimeter that burned circa 1940 near Cherskiy in northeastern Siberia. At each stand we measured photosynthetically active radiation (PAR), air temperature, and relative humidity at 1 meter (m) above the ground, and measured soil moisture and temperature at the interface between the organic and mineral soil horizons (~10 centimeter (cm) depth), and also within the mineral soil 10cm below the organic-mineral interface. Data collection began in July of 2014 and is ongoing, though there are gaps due to power outages. Canopy shading reduces PAR at higher density sites, and leads to lower soil temperatures during the growing season. Soil temperatures are also lower in higher density stands during winter, while soil moisture patterns are less clearly related to forest density.生态系统通过影响地表能量平衡，调控多年冻土土壤的热动态变化。因此植被结构与功能的改变，有可能改变多年冻土土壤的热特性，并对土壤碳循环产生连锁影响。在西伯利亚寒温带针叶林中，林木株密度与冠层覆盖度受野火烈度影响。本研究针对6处林分样地开展林下空气与土壤微气象特征差异的分析：其中2处为高密度样地（冠层覆盖度＞75%）、2处为中密度样地（冠层覆盖度25%~50%）、2处为低密度样地（冠层覆盖度＜25%），所有样地均位于西伯利亚东北部切尔斯基（Cherskiy）附近一处1940年左右过火的火迹地内。针对每处样地，我们测定了地面1米高度处的光合有效辐射（Photosynthetically Active Radiation, PAR）、气温与相对湿度；同时测定了有机土层与矿质土层界面处（约10厘米深度）的土壤含水率与温度，以及该界面下方10厘米处的矿质土层内的土壤温湿度。数据采集工作始于2014年7月，目前仍在持续，但因停电问题存在部分数据缺失。冠层遮阴会降低高密度样地的光合有效辐射水平，并导致生长季内土壤温度降低；冬季时高密度林分的土壤温度同样更低，但土壤含水率的分布格局与林分密度的关联相对较弱。