Toward biologically meaningful net carbon exchange estimates for tall, dense canopies: Multi-level eddy covariance observations and canopy coupling regimes in a mature Douglas-fir forest in Oregon
Toward biologically meaningful net carbon exchange estimates for tall, dense canopies: Multi-level eddy covariance observations and canopy coupling regimes in a mature Douglas-fir forest in Oregon
复制标题
DOI：
10.1016/j.agrformet.2013.01.001
复制
发表时间：
2012-12
影响因子：
6.2
通讯作者：
Christoph K. Thomas;Jonathan G Martin;B. Law;K. Davis
中科院分区：
文献类型：
--
作者：
Christoph K. Thomas;Jonathan G Martin;B. Law;K. Davis
我们试图提高净生态系统交换（NEE）的估计，高大，密集，成熟的道格拉斯冷杉林在俄勒冈州海岸范围内的特点是弱流，系统的风向切变，有限的湍流混合在整个昼夜期间。我们使用涡度协方差（EC）观测在两个层次上，并在6年（2006-2011年）收集的碳和水通量的同步生物测量，以开发和测试一个概念框架，以（i）减少不确定性，通过保留更多的测量计算每年的NEE总和和（ii）产生可验证的和生物意义的估计，通过占失踪的子冠层呼吸。该框架假设：（a）垂直层之间的标量交换可以归类为离散的冠层耦合制度和（B）平流导致标量的系统性损失，从观测量，可以间接估计和占亚冠层呼吸通量时，冠层解耦。期间与解耦的子冠层占主导地位，并占据65%和88%的白天和夜间期间，分别。根据新框架得出的年NEE估计为480 gCm − 2 year −1，与使用临界摩擦速度过滤的单水平EC数据的传统估计相比减少了620 gCm − 2 year − 1。减少NEE是由于增强生态系统呼吸（RE），而总生态系统生产力保持不变。改进的RE估计值与基于土壤、茎和叶呼吸的独立估计值在3%以内一致。新框架的风险和局限性进行了讨论。我们的结论是，同时以上和子冠层EC观测是必不可少的，以衡量一个有意义的碳平衡，在高大，茂密的森林，因为他们不借给自己传统的，标准化的处理。新的框架可能有助于将更多高大茂密的森林纳入全球碳循环合成和建模工作。
We sought to improve net ecosystem exchange (NEE) estimates for a tall, dense, mature Douglas-fir forest in the Oregon Coast range characterized by weak flows, systematic wind directional shear, and limited turbulent mixing throughout the diurnal period. We used eddy covariance (EC) observations at two levels and concurrent biological measurements of carbon and water fluxes collected over a period of 6 years (2006–2011) to develop and test a conceptual framework to (i) reduce uncertainty by retaining more measurements for the computation of annual NEE sums and (ii) produce defendable and biologically meaningful estimates by accounting for the missing sub-canopy respiration. The framework assumes that (a) the scalar exchange between vertical layers can be categorized into discrete canopy coupling regimes and (b) advection leads to a systematic loss of scalar from the observational volume that can indirectly be estimated and accounted for as sub-canopy respiration flux when canopy layers are decoupled. Periods with a decoupled sub-canopy layer dominated and occupied 65 and 88% of the day- and nighttime periods, respectively. Annual NEE derived from the new framework was estimated as 480gCm−2year−1, which was reduced by 620gCm−2year−1compared to traditional estimates from single-level EC data filtered using a critical friction velocity. The reduced NEE was due to an enhanced ecosystem respiration (RE), while gross ecosystem productivity remained unchanged. Improved RE estimates agreed well with those from independent estimates based on soil, stem, and foliage respiration within 3%. Risks and limitations of the new framework are discussed. We conclude that concurrent above- and sub-canopy EC observations are essential to measure a meaningful carbon balance in tall, dense forests since they do no lend themselves to traditional, standardized processing. The new framework may help to include more tall and dense forests in global carbon cycle synthesis and modeling efforts.