8. LAI (Leaf Area Index)¶

8.1. Key Facts¶

Varies with phenology (state of the vegetation e.g. leaf on or leaf off, bud burst).
Measure of the area of leaf surface relative to the ground area. If you look up at an adult, healthy tree there will be typically many layers of leaves between the ground and the top of the canopy. Hence the LAI values are typically greater than 1 m² m^-2.
Units: m² m^-2

8.2. Porosity¶

If air can blow through an object (e.g. a tree) it is more porous than those one the that air can not (e.g. buildings). The latter are referred to as bluff bodies. Trees porosity may change through the year with phenology. For example, when deciduous plants lose their leaves (fall off) they become more porous.

8.3. Measuring LAI¶

Direct measurements

Destructive sampling - measuring the area of all the leaves of a tree
Collect all the leaves that fall off and measuring their area

Indirect measurements

Measurements (above and below the canopy) of radiation (e.g. using LAI-2000, LI-COR) which are then used to infer LAI
Satellite based products e.g. MODIS)

8.4. Model LAI¶

Depends on:
- temperature (growing degree days)
- solar radiation/day length

8.5. Parameters LAI influences¶

Albedo
Roughness length and displacement
Aerodynamic resistance
Surface/ canopy resistance

For assignment we needs a simple measure of the value and how it varies. For example, do you expect the LAI to vary through the year for the land cover you are looking at? If yes, when should it increase/ decrease? What is an approximate maximum (typical value)?