Abstract

Extensive studies are available that analyse time series of carbon dioxide and water flux measurements of FLUXNET sites over many years and link these results to climate change such as changes in atmospheric carbon dioxide concentration, air temperature and growing season length and other factors. Many of the sites show trends to a larger carbon uptake. Here we analyse time series of net ecosystem exchange, gross primary production, respiration, and evapotranspiration of four forest sites with particularly long measurement periods of about 20 years. The regular trends shown are interrupted by periods with higher or lower increases of carbon uptake. These breakpoints can be of very different origin and include forest decline, increased vegetation period, drought effects, heat waves, and changes in site heterogeneity. The influence of such breakpoints should be included in long-term studies of land-atmosphere exchange processes.

摘要

已有大量研究分析了FLUXNET站点多年的二氧化碳和水通量测量值的时间序列，并将这些结果与气候变化联系在一起，例如大气中二氧化碳浓度，空气温度和生长期的长短以及其他因素的变化。许多站点都显示出更大的碳吸收趋势。在这里，我们分析了四个森林站点的净生态系统交换，初级总产值，呼吸作用和蒸散量的时间序列，测量时间特别长，大约为20年。所示的规律性趋势会被碳吸收量增加或减少的时期打断。这些断点的来源可能非常不同，包括森林退化，植被增加，干旱影响，热浪以及站点异质性的变化。