Abstract
Tropical, temperate, and boreal forests are the subject of various eddy covariance studies, but less is known about the subtropical region. As there are large areas of subtropical forests in the East Asian monsoon region with possibly high carbon uptake, we used three years (2011–2013) of eddy covariance data to estimate the carbon balance of a subtropical mountain forest in Taiwan. Two techniques of flux partitioning are applied to evaluate ecosystem respiration, thoroughly evaluate the validity of the estimated fluxes, and arrive at an estimate of the yearly net ecosystem exchange (NEE). We found that advection is a strong player at our site. Further, when used alone, the nighttime flux correction with the so-called u∗ method (u∗ = friction velocity) cannot avoid underestimating the nighttime respiration. By using a two-technique method employing both nighttime and daytime parameterizations for flux corrections, we arrive at an estimate of the three-year mean NEE of −561 (±standard deviation 114) g·C·m−2·yr−1. The corrected flux estimate represents a rather large uptake of CO2 for this mountain cloud forest, but the value is in good agreement with the few existing comparable estimates for other subtropical forests.
Highlights
It is well accepted that the eddy covariance technique is most suitable for quantifying CO2 fluxes for sites with long fetches, flat terrain, and an overall very homogenous surface [7]
Is study is based on a three-year (2011–2013) data set of eddy covariance measurements of CO2 fluxes above a subtropical mountain forest in Taiwan
For the investigation of the yearly CO2 net ecosystem exchange (NEE), a detailed analysis of the quality of the measured fluxes is performed. e local meteorology is analysed in detail, and the contribution of the ecosystem respiration to NEE is estimated by using a combination of several flux partitioning techniques
Summary
It is well accepted that the eddy covariance technique is most suitable for quantifying CO2 fluxes for sites with long fetches, flat terrain, and an overall very homogenous surface [7]. It is, a challenge to obtain reliable estimates of yearly carbon uptake by photosynthesis in mountainous. For the investigation of the yearly CO2 net ecosystem exchange (NEE), a detailed analysis of the quality of the measured fluxes is performed. E local meteorology is analysed in detail, and the contribution of the ecosystem respiration to NEE is estimated by using a combination of several flux partitioning techniques. We develop an improved estimate of the annual carbon uptake of the subtropical forest in complex terrain by including the best estimate of ecosystem respiration into the carbon balance evaluation
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