Reliability of net ecosystem productivity estimation in an Alaskan boreal forest from satellites

我们把西伯利亚东部的落叶松林和阿拉斯加的云杉林作为永久冻土上的代表性森林。落叶松和云杉分别占西伯利亚东部和阿拉斯加面积的80%和70%。利用对地观测卫星上的传感器估算了净生态系统生产力（NEP）和森林火灾对NEP的影响。我们评估了未受森林火灾破坏的森林的碳预算，阿拉斯加黑森林的火灾严重程度，以及西伯利亚东部的树冠和地表火灾。基于野外苔藓和森林成分的光谱观测，建立了基于遥感数据估算森林地表植被、冠层净初级生产力（NPP）和叶面积指数的方法，并应用于阿拉斯加云杉和西伯利亚落叶松森林。我们估算了冠层叶面积指数和森林地表植被组成。在此基础上，结合野外观测，评价了林冠叶面积指数与林冠NPP、林底植被组成和林底NPP、NEP地理分布之间的关系。此外，我们还测量了包括苔藓、地衣和烧痕在内的森林地面的光谱反射率，以评估烧痕对火灾后植被恢复的影响。在阿拉斯加黑云杉林中，利用线性方程（决定系数R^2=0.6）从50m×50m面积中平均绿带和红带的比例估算苔藓的分数面积。由于保留了许多部分的苔藓，恢复的主要是云杉。由于只剩下一小部分藓类植物，将以阔叶树如桦树为主。估算剩苔面积是估算火灾后新能源效益的主要指标。

We focused on a larch forest in eastern Siberia and a spruce forest in Alaska as representative forests that exist on permafrost. Larch and spruce occupies 80% and 70% of the area in eastern Siberia and Alaska, respectively. We estimated net ecosystem productivity (NEP) and forest fire effects on the NEP using sensors onboard earth observation satellites. We evaluated carbon budgets of forests that were not damaged by forest fires, fire severity of Alaskan black forest, and crown and surface fires in eastern Siberia. Based on field spectral observations of mosses and forest component, we built a methodology for estimating forest floor vegetation as well as canopy net primary productivity (NPP) and leaf area index from the remotely sensed data, and we applied to Alaskan spruce and Siberian larch forests. We estimated canopy leaf area index and forest floor vegetation composition. Based on these relationships and field observations, we evaluated the relationship between canopy leaf area index and canopy NPP, forest floor vegetation composition and forest floor NPP, and geographical distribution of NEP. Further, we measured spectral reflectances of forest floor including mosses, lichens, and burnt scars to evaluate effects of burnt scars and vegetation recovery after the fire. In the Alaskan black spruce forest, fractional area of mosses were estimated from the ratio of green and red bands averaged in 50m×50m area using a linear equation (coefficient of determination R^2=0.6). As the many portion of the mosses remained, recovery of spruce will be predominant. As small part of mosses remained, broad leaf trees such as birch will be predominant. The estimated fractional area of remained mosses was the main index for estimating NEP after the fire.