NPP Boreal Forest: Consistent Worldwide Site Estimates, 1977-1994

The three objectives of this study were: (1) to summarize net primary productivity (NPP) and carbon allocation patterns for boreal forests, (2) to examine relationships between climatic and biological variables and NPP, and (3) to examine carbon allocation coefficients for all boreal forests or types of boreal forests that can be used to estimate NPP from easily measured components of NPP. Twenty-four Class I boreal forest stands (complete NPP budgets) and 45 Class II stands (aboveground NPP - ANPP - budget only) were identified. The geographic distribution of the Class I stands was not uniform; 46 percent of the stands were from two studies in North America and only one stand was from the important larch forests of Eurasia. Total (above- and below-ground) net primary productivity (NPP) ranged from 52 to 868 gC/m2/yr and averaged 424 gC/m2/yr. ANPP was consistently larger for deciduous than evergreen boreal forests in each of the major boreal regions, especially for boreal forests in Alaska. Ratios of belowground net primary productivity (BNPP) to total net primary productivity (BNPP:TNPP) were consistently larger for evergreen (0.36) than deciduous (0.19) boreal forests. NPP of different-aged stands in age sequence varied from 44 to 77 percent - a magnitude equal or greater to that of climatic factors or vegetation type. NPP and ANPP were positively correlated (r2 = 0.66 to 0.68) to mean annual aboveground increment for Class I stands and this empirical relationship explained 81 percent of the observed variation of ANPP for Class II stands. These robust relationships provide an approach for increasing the number and spatial coverage of boreal forest NPP data needed to evaluate NPP estimates from ecosystem models. Notable deficiencies of boreal forest NPP data were: ground layer vegetation and belowground NPP data, NPP data for boreal forest age sequences, and NPP data for boreal larch ecosystems in Eurasia.

本研究的三大目标为：(1) 总结北方针叶林的净初级生产力（net primary productivity, NPP）与碳分配模式；(2) 探究气候与生物变量和净初级生产力之间的关联；(3) 梳理适用于所有北方针叶林或其林型的碳分配系数，以便通过易于测定的净初级生产力组分估算净初级生产力。
本研究共筛选得到24个I级北方针叶林林分（具备完整净初级生产力预算）以及45个II级林分（仅包含地上净初级生产力（aboveground NPP, ANPP）预算）。I级林分的地理分布并不均匀：其中46%的林分来自北美地区的两项研究，仅1个林分取自欧亚大陆重要的落叶松林生态系统。
总净初级生产力（total net primary productivity, TNPP，涵盖地上与地下部分）的取值范围为52~868 gC/m²/年，平均值为424 gC/m²/年。
在各主要北方针叶林分布区中，落叶型北方针叶林的地上净初级生产力始终高于常绿型北方针叶林，这一差异在阿拉斯加地区的北方针叶林中尤为显著。
地下净初级生产力（belowground NPP, BNPP）与总净初级生产力的比值（BNPP:TNPP）在常绿型林分中为0.36，显著高于落叶型林分的0.19。
不同林龄序列林分的净初级生产力取值介于44%~77%之间，其变化幅度不低于气候因子或植被类型带来的影响。
对于I级林分，净初级生产力与地上净初级生产力均与年平均地上增量呈显著正相关（决定系数r²=0.66~0.68）；该经验关系可解释II级林分地上净初级生产力81%的观测变异。
上述稳健的相关关系为扩大北方针叶林净初级生产力数据的样本量与空间覆盖范围提供了可行路径，可用于评估生态系统模型所估算的净初级生产力结果。
当前北方针叶林净初级生产力数据仍存在显著短板：缺乏地表层植被与地下净初级生产力相关数据、北方针叶林林龄序列的净初级生产力数据，以及欧亚大陆北方落叶松林生态系统的净初级生产力数据。