Indirect contact method

In forest stands, direct estimates of vegetative LAI are often derived from the allometric relationship between leaf area per tree and diameter at breast height (DBH). An allometric equation relates the stem diameter to leaf area with log y — a + b log(x) [3]

Where y is the leaf area (in square meters) and x is the stem diameter (in cm) at DBH. The coefficients, a and b, vary with plant species, tree size, nutrient availability, and fertilization. When accurate estimates of LAI are needed, site-specific allometric equations should be developed.

The point quadrats method offers another way of measuring leaf area indirectly. It pierces a vegetation canopy with a long thin needle under known elevation (i.e., the angle between the needle and the horizontal plane when vertically projected) and azimuth angles (i.e., the bearing of the needle from north when horizontally projected) and counting the number of hits or contacts of the needle with 'green' canopy elements. The vegetation LAI is determined by the following formula:

where Ni is the number of contacts of the needle with the vegetation with elevation i, and Kj the extinction coefficient with elevation i. The point quadrats method is suitable for short vegetation with large leaves but not for forests.

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