Leaf Area Index Models

Abstract

Leaf area index (LAI), one half the total green leaf area per unit horizontal ground surface, is an important structural property of vegetation. Because leaf surfaces are the primary border of energy and mass exchange, important processes such as canopy interception, evapotranspiration, and gross photosynthesis are directly proportional to LAI. This article discusses how to obtain LAI, the global LAI characteristics, and how LAI is applied in ecological models. The current state of the art in obtaining LAI can be broken into the ground-based methods and the remote-sensing methods. In the field, LAI can be estimated directly or indirectly: direct methods measure LAI through litterfall or destructive sampling; indirect methods estimate LAI via relationships with other more easily measurable parameters, such as canopy transmittance. Current methods for estimating LAI from optical remote sensing are classified into three categories through: (1) empirical relationships between LAI and vegetation indices; (2) inversion of canopy reflectance models; and (3) a hybrid inversion method. Following this, several current satellite sensors that provide LAI products will be introduced. The spatial and temporal properties of global LAI products are analyzed. Finally, how the LAI is applied in various ecological models is discussed.