A long-standing goal of ecology has been to understand the cycling of carbon in forests. This has taken on new urgency with the need to address a rapidly changing climate. Forests serve as long-term stores for atmospheric CO₂, but their continued ability to take up new carbon is dependent on future changes in climate and other factors such as age. We have been measuring many aspects of carbon cycling at an unmanaged evergreen forest in central Maine, USA, for over 25 years. Here we use these data to address questions about the magnitude and control of carbon fluxes and quantify flows and uncertainties between the different pools. A key issue was to assess whether recent climate change and an aging tree population were reducing annual C storage. Total ecosystem C stocks determined from inventory and quantitative soil pits were about 23,300 g C m⁻² with 46% in live trees, and 48% in the soil. Annual biomass increment in trees at Howland Forest averaged 161 ± 23 g C m⁻² yr⁻¹, not significantly different from annual net ecosystem production (NEP = −NEE) of 211 ± 40 g C m⁻² y⁻¹ measured by eddy covariance. Unexpectedly, there was a small but significant trend of increasing C uptake through time in the eddy flux data. This was despite the period of record including some of the most climate-extreme years in the last 125. We find a surprising lack of influence of climate variability on annual carbon storage in this mature forest.

中文翻译：

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多年碳循环测量表明 Howland Forest AmeriFlux 站点对外部变化驱动因素的抵抗力

生态学的一个长期目标是了解森林中的碳循环。由于需要应对迅速变化的气候，这具有新的紧迫性。森林是大气 CO ₂的长期储存库，但它们持续吸收新碳的能力取决于未来气候变化和年龄等其他因素。25 年来，我们一直在美国缅因州中部未经管理的常绿森林中测量碳循环的许多方面。在这里，我们使用这些数据来解决有关碳通量大小和控制的问题，并量化不同池之间的流量和不确定性。一个关键问题是评估最近的气候变化和树木老化是否会减少年度碳储存量。根据清单和定量土壤坑确定的总生态系统碳库约为 23,300 g C m ^-2，其中 46% 存在于活树中，48% 存在于土壤中。Howland Forest 树木的年生物量增量平均为 161 ± 23 g C m ^-2  yr ^-1, 与通过涡度协方差测量的 211 ± 40 g C m ^-2  y ^{-1 的}年净生态系统产量 (NEP = -NEE) 没有显着差异。出乎意料的是，在涡流数据中存在随时间增加 C 吸收增加的小但显着的趋势。尽管有记录的时期，包括过去 125 年中气候最极端的一些年份。我们发现气候变率对这片成熟森林的年碳储存量的影响令人惊讶地缺乏。