Leaf Area Index Data, Victorian Dry Eucalypt SuperSite, Whroo, 2015

Leaf area index (LAI) can be defined as the total one sided area of leaf tissue per unit area of ground and is a key derived parameter that is associated with water and light interception, radiation transfer, water and carbon exchange (Bréda, 2003). Canopy cover can be defined as the fraction of ground shaded by the vertical projection of tree crowns (Walker et al. 1981). These measures may be used as proxies for actual canopy leaf area. Leaf area index is the preferred measure of cover for vegetation and as a key variable used in total biomass estimation and in carbon cycling prediction models. Indirect measures of LAI include digital photographic methods using flat or hemispherical images, referred to respectively as DCP (digital cover photography) and DHP (digital hemispheric photography). LAI measurements are carried out at each SuperSite using the most appropriate method for the vegetation type present. Digital Cover Photography (DCP) is recommended for medium stature (10-40 m) vegetation with simple structure. DCP was originally developed for sparse to moderately dense broadleaf forest and has also been tested in sparse savanna woodland. DCP is recommended for these vegetation types and has also been suggested for more dense forests (Pekin and MacFarlane 2009). Digital Hemispheric Photography (DHP) is recommended for short vegetation (4-8 m) e.g. low banksia woodland, complex (multi strata) and tall vegetation (> 40+ m) using images taken 20 m apart (MacFarlane et al. 2007).

叶面积指数（Leaf Area Index, LAI）可定义为单位地面面积上的叶片组织单侧总表面积，是与水分与光能截获、辐射传输、水碳交换密切相关的关键衍生参数（Bréda, 2003）。冠层覆盖度（Canopy cover）可定义为树冠垂直投影所遮蔽的地面比例（Walker et al. 1981）。上述指标可作为实际冠层叶面积的替代表征参数。叶面积指数是植被覆盖度的优选衡量指标，同时也是总生物量估算及碳循环预测模型中的关键变量。叶面积指数的间接测量方法包括采用平面影像或半球影像的数码摄影技术，二者分别称为数码覆盖摄影（Digital Cover Photography, DCP）与数码半球摄影（Digital Hemispheric Photography, DHP）。各超级站点（SuperSite）会根据所在地的植被类型，选用最适宜的方法开展叶面积指数测量。数码覆盖摄影（DCP）推荐用于结构简单的中等株高（10~40米）植被。该方法最初专为稀疏至中等密度的阔叶森林开发，也曾在稀疏稀树草原林地中开展测试，适用于上述植被类型，同时也被建议应用于更茂密的森林（Pekin and MacFarlane 2009）。数码半球摄影（DHP）推荐用于矮生植被（4~8米，如低矮班克木林地）、复层（多层结构）植被以及高大植被（>40米），拍摄时的影像间隔为20米（MacFarlane et al. 2007）。