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.

生态系统通过改变地表能量平衡（surface energy balance），调控多年冻土土壤（permafrost soils）的热动力学特性。因此，植被结构与功能的变化有可能改变多年冻土土壤的热学特性，并对土壤碳循环产生连锁效应。在西伯利亚北方针叶林（boreal forests）中，林木株密度与林冠覆盖度受野火烈度（wildfire severity）的影响。本研究选取6处林分（stand），分析其林下空气与土壤微气象学（micrometeorology）特征的差异：其中2处为高密度林分（林冠覆盖度＞75%）、2处为中密度林分（林冠覆盖度25%~50%）、2处为低密度林分（林冠覆盖度＜25%），所有林分均位于西伯利亚东北部切尔斯基附近一处约1940年过火的单一火迹地（fire perimeter）内。在每处林分中，我们于地面上方1米处测定了光合有效辐射（photosynthetically active radiation, PAR）、空气温度与相对湿度；同时在有机层与矿质层土壤界面（约10厘米深度）以及该界面下方10厘米的矿质土层中，测定了土壤含水率与土壤温度。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。林冠遮阴会降低高密度林分的光合有效辐射水平，并在生长季降低土壤温度；冬季高密度林分的土壤温度同样更低，不过土壤含水率的分布格局与森林密度的相关性并不显著。