The Leaf Area Index measures the area of leaves and needles per unit of ground area. For deciduous trees, it can be estimated by examining the litterfall. If trees are felled as part of forestry activities, an examination of the crown can be used for the determination of the Leaf Area Index. Additionally, optical methods are used to measure the Leaf Area Index. These include, for example, photographic approaches from below the canopy with subsequent image analysis.

Among other things, the leaf area index contributes to the understanding of the following processes in forest ecosystems:

• Photosynthesis (carbon uptake, transpiration, light absorption)
• Evaporation from the forest floor and transpiration of ground vegetation (shading)
• Changes in the composition of ground vegetation (shading)
• Release of volatile organic compounds (VOCs)
• Influence on filtering effect of forests (air pollutants)