广西桉树人工林叶面积指数的估测及其校正

叶面积指数(Leaf area index, LAI)是森林生态系统重要的结构参数，通过遥感技术可反演区域LAI,但其可靠性需要地面准确的实测数据进行验证。选取广西国有高峰林场不同林龄的桉树(Eucalyptus robusta)人工林为对象，以异速生长法(Allometry)为对照，综合利用植物冠层分析仪法(LAI-2200)、跟踪辐射和冠层结构分析仪法(TRAC)、半球摄影法(DHP)以及地基激光雷达法(TLS)等间接法估测样地的LAI,并考虑木质成分以及聚集效应影响，进行相应的校正处理，为地面快速、准确测量桉树人工林LAI提供参考。结果表明：桉树人工林的比叶面积为125.37±13.38 cm~2/g,通过Allometry获得的LAI变化范围在1.65—3.84,平均为2.73,不同林龄间的差异均显著(P<0.05),随着林龄的增加呈现先增加后减少的趋势。在未校正情况下，LAI-2200、TRAC、DHP、TLS估算的LAI存在显著差异(P<0.05)。与对照相比，LAI-2200在幼龄林和过熟林中估算误差最小，TRAC在成熟林中估算误差最小。相对于完全去除法，利用...

Leaf area index estimation and correction of Eucalyptus plantation in Guangxi Autonomous Region

Leaf area index (LAI) is an important structural parameter of forest ecosystem, and the regional LAI can be retrieved through remote sensing technology. However, due to the complexity of forest structure and the heterogeneity of ground features, its reliability needs to be verified by accurately measured data on the ground. Using Eucalyptus plantation of different ages in the Guangxi State-owned Gaofeng Forest Farm as the object and the Allometry method as the control, this study uses indirect methods such as LAI-2200 plant canopy analyzer (LAI-2200), tracing radiation and architecture of canopies (TRAC), digital hemispherical photography (DHP), and terrestrial laser scanning (TLS) to estimate the LAI of the sample plots. The study also takes into account the influence of wood elements and clumping effect to conduct corresponding correction treatment, which provides a reference for the quick and accurate measurement of the LAI of Eucalyptus plantation on the ground. The results showed that the specific leaf area of Eucalyptus plantation was 125.37±13.38 cm²/g, and the LAI obtained by the Allometry method ranged from 1.65 to 3.84, with an average of 2.73. The differences between different forest ages were significant (P<0.05), showing a trend of first increasing and then decreasing as the forest age increased. Without correction, there were significant differences in the LAI estimated by LAI-2200, TRAC, DHP, and TLS (P<0.05). Compared with the control, LAI-2200 had the smallest estimation error in young and over-mature forests, and TRAC had the smallest estimation error in mature forests. LAI was generally underestimated by different indirect methods. Without considering the correction, the LAI-2200 is the most suitable choice, which can obtain accurate LAI. It is necessary to further consider automatic exposure problems during measurement of LAI by DHP. For TLS, it is necessary to further consider the inversion model according to the forest stand environment and use airborne laser scanning (ALS) to appropriately supplement the point cloud data above the canopy to improve the accuracy of the inversion. Compared with the complete removal method, it is more reasonable to use the PS imitation method to correct the wood''s influence in Eucalyptus plantation. The woody-to-total area ratio is between 0.33% and 25.95%, and the clumping index is between 0.63 and 1.00. Both have the same degree of impact on the estimation of LAI by the indirect methods. It is found that the correction effect is not obvious. Because there is an offsetting role in the removal of wood elements and clumping effect.