What is Leaf area index? — Biology

Definition 3.7 University Biology — Year 1 · Chapter 3 — Functional Organization of a Flowering Plant

The leaf area index $L$ of a plant cover is the total one-sided leaf area per unit area of ground. A meadow in June has $L \approx 3$ , a deciduous forest $4\text{ to }6\,$ , a tropical rain forest up to $8\,$ : several layers of leaf are stacked above every square metre of soil.

Light under a canopy against leaf area index, for three leaf orientations. Beyond L 6 an extra layer of leaves gains almost nothing, which is why canopies stop there. — Light under a canopy against leaf area index, for three leaf orientations. Beyond $L \approx 6$ an extra layer of leaves gains almost nothing, which is why canopies stop there.

Examples

Example 3.10 (The oak’s two surfaces)

An oak whose crown shades $100\,\mathrm{m}^{2}$ at $L = 5$ carries $500\,\mathrm{m}^{2}$ of leaf. Its fine roots, at a few kilometres per cubic metre through $100\,\mathrm{m}^{3}$ of soil, offer several hundred square metres, and their root hairs a thousand more: the absorbing surface underground is several times the photosynthetic surface above, over the same square metres of ground.

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