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Leaf area index (m2 rrr2)

ductance of the soil is as large as that from plants, as long as the soil surface is wet. For LAI < 1 surface conductance increases again, i.e. sparse vegetation cover protects the soil from loss of water, but the component regulated by the plant is very small. In this case "water saving" by plants does not affect the water loss from the site, because the water balance is determined by evaporation from the soil (Greenwood et al. 1992). In Fig. 2.2.19 data from measured plant stands are included. It becomes obvious that the maximum stoma-tal conductance of the plant cover of the earth is between 4 and 12 mm s_1. Whilst herbaceous vegetation is characterised by a high LAI and high canopy conductance, forests and shrubs have a low LAI and low conductance. The reason for this difference is the coupling of the vegetative types to the atmosphere. The high conductance does not mean that herbaceous vegetation transpires more than forest stands.

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