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植物叶片组织的单侧总表面积，是关联水分与光照截获、辐射传输、水碳交换的关键衍生参数（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）。上述两类指标均可作为实际冠层叶面积的替代表征。叶面积指数是植被覆盖评估的首选指标，同时也是总生物量估算及碳循环预测模型中的核心变量。叶面积指数的间接测定方法包括基于平拍或半球影像的数码摄影技术，分别对应数码冠层摄影法（Digital Cover Photography, DCP）与数码半球摄影法（Digital Hemispheric Photography, DHP）。研究团队会在每个超级监测点（SuperSite）结合现场植被类型，选用最适配的叶面积指数测定方法。数码冠层摄影法（DCP）适用于结构简单的中等高度（10~40米）植被，该方法最初为稀疏至中等密度的阔叶森林开发，同时也在稀树草原林地中完成了测试验证。针对上述植被类型推荐使用数码冠层摄影法，且已有研究建议其可应用于更茂密的森林（Pekin & MacFarlane, 2009）。数码半球摄影法（DHP）则适用于低矮植被（4~8米，如低矮班克木林地）、多层结构的复杂植被以及高度超过40米的高大植被，影像采集间距需设置为20米（MacFarlane et al., 2007）。