中文摘要：

利用光学仪器法能够快速、高效地测定森林生态系统的叶面积指数（leaf area index, LAI）。然而, 评估该方法测定针阔混交林LAI季节动态准确性的研究较少。该研究基于凋落物法测定了小兴安岭地区阔叶红松（Pinus koraiensis）林LAI的季节动态, 其结果可代表真实的LAI。参考真实的LAI, 对半球摄影法（digital hemispherical photography, DHP）和LAI-2000植物冠层分析仪测定的有效叶面积指数（effective LAI, Le）进行了评估。首先对DHP测定LAI过程中采用的不合理曝光模式（自动曝光）进行了系统校正。同时, 测定了光学仪器法估测LAI的主要影响因素（包括木质比例（woody-to-total area ratio, α）、集聚指数（clumping index, ΩE）和针簇比（needle-to-shoot area ratio, γE））的季节变化。结果表明： 3种不同方法测定的LAI均表现为单峰型的季节变化, 8月初达到峰值。从5月至11月, DHP测定的Le比真实的LAI低估50%–59%, 平均低估55%; 而LAI-2000植物冠层分析仪测定的Le比真实的LAI低估19%–35%, 平均低估27%。DHP测定的Le 经过自动曝光, α、ΩE和γE校正后, 精度明显提高, 但仍比真实的LAI低估6%–15%, 平均低估9%; 相对而言, LAI-2000植物冠层分析仪测定的Le经过α、ΩE和γE校正后, 精度明显提高, 各时期与真实的LAI的差异均小于9%。研究结果表明, 考虑木质部和集聚效应对光学仪器法的影响后, DHP和LAI-2000植物冠层分析仪均能相对准确地测定针阔混交林LAI的季节动态, 其中, DHP的测定精度高于85%, 而LAI-2000植物冠层分析仪的测定精度高于91%。

英文摘要：

Aims Leaf area index （LAI） is a commonly used parameter for quantifying canopy structure and can be quickly measured by indirect optical methods in a forest stand, but few studies have evaluated the accuracy of optical methods to estimate seasonal variations of LAI in a mixed conifer-broadleaved forest. The aims of this study are to （1） develop a practical field method for directly measuring seasonal variations in LAI for mixed conifer-broadleaved forest; （2） evaluate the accuracy of optical methods （digital hemispherical photography （DHP） and LAI-2000 plant canopy analyzer） for measuring the seasonality of LAI; and （3） determine how much the accuracy of estimating the seasonality of LAI can be improved by using optical methods after correcting for influencing factors （e.g., woody materials and clumping effects within a canopy）. Methods The seasonal variations of LAI in a mixed broadleaved-Korean pine （Pinus koraiensis） forest were estimated from litterfall and used to evaluate optical LAI （effective LAI, Le） measurements using the DHP and the LAI-2000 plant canopy analyzer. We corrected a systematic error due to incorrect automatic photographic exposure for DHP measurements. In addition to optical Le, we also measured the seasonality of other major factors influencing the determination of LAI, including woody-to-total area ratio （α）, clumping index （ΩE） and needle-to-shoot area ratio （γE）. Important findings The LAI from different methods all showed a unimodal form, and peaked in early August. Effective LAIs from the optical methods underestimated LAI throughout the growing seasons （from May to November）. Le from DHP underestimated LAI by an average of 55% （ranging from 50% to 59%） and from LAI-2000 plant canopy analyzer by an average of 27% （ranging from 19% to 35%）. The accuracy of Le from DHP after correcting for the automatic exposure, α, ΩE and γE was greatly improved, but the LAI was underestimated by 6%–15% （with mean value of 9%） f