Leaf Area Index at Harvard Forest HEM and LPH Towers since 1998

Leaf area index (LAI) measurements are made to detect changes in forest leaf area that are important in understanding forests’ carbon dioxide (CO2) uptake and water use. Measurements of LAI in different forest types are useful understanding differences between forests in CO2 uptake and water use, while variation in LAI in the same forest type over time helps to explain interannual variation and long-term trends in carbon storage and water use. Within a single year, especially for deciduous forests, seasonal changes in LAI are very important in determining the forest’s cycle of CO2 uptake and water use. LAI measurements at Harvard Forest were begun in the old-growth hemlock stand in 1998 in order to understand and develop a predictive model for its carbon exchange, and were begun at the Little Prospect Hill site in 2002 to better understand CO2 uptake and carbon storage at this site, which were measured by the eddy-covariance method beginning in 2002. Due to a lack of personnel, multiple annual measurements of LAI to examine seasonal change in leaf area did not begin until 2007.叶面积指数（Leaf Area Index，LAI）测量旨在检测森林叶面积的变化，这对理解森林的二氧化碳（CO₂）吸收与水分利用过程具有核心意义。针对不同森林类型的叶面积指数测量，有助于明晰不同森林在二氧化碳吸收与水分利用方面的差异；而同一森林类型的叶面积指数随时间的变化，则可用于阐释碳储量与水分利用的年际波动及长期趋势。在单一年度内，尤其是落叶林，叶面积指数的季节变化对确定森林的二氧化碳吸收与水分利用循环至关重要。1998年，研究团队在哈佛森林（Harvard Forest）的原生铁杉林分启动了叶面积指数测量工作，以探究并构建该林分的碳交换预测模型；2002年，又在小展望山（Little Prospect Hill）站点开展了该项测量，以更深入地理解该站点的二氧化碳吸收与碳储量特征——该站点的相关观测自2002年起采用涡度协方差法（Eddy Covariance Method）完成。由于人员不足，为探究叶面积季节变化而开展的多次年度叶面积指数测量直至2007年才正式启动。