22 Leaf Diffusive Conductances
in the Major Vegetation Types of the Globe
Ch. Korner
22.1 The Significance of Leaf Conductances in Vegetation Modeling
Water availability is a key determinant of growth and distribution of individual plants as well as vegetation. In turn, plant coverage of landscapes
influences terrestrial water storage, and - by controlling evapotranspiration
- feeds back on the climate and soil moisture regimes. Because of this
interrelation of plant functioning with climate and soils, plant control of
vapor loss is an important component of biosphere as well as global circulation models.
By far the largest fraction of terrestrial evaporative water loss passes
through the microscopic stomata pores of plant leaves. It is estimated that
this pathway accounts for 70% of the evaporative vapor loss in Europe
(Maniak 1988), and similar values may apply to other regions. The degree of
stomatal opening, expressed as the diffusive conductance of leaves for water
vapor (g), is controlled by physiological processes, which themselves respond to environmental conditions such as photon flux density, soil, or
atmospheric moisture. The maximum rate of vapor loss of vegetation for
any given meteorological situation is determined by the maximum diffusivity
of leaves (i.e., the number and geometry of stomatal pores), and the total
amount of leaf area per unit of land area (the leaf area index, LAI). At
any given leaf conductance the most important climatic determinants of
transpiration are the moisture deficit of the atmosphere and the aerodynamic conditions in and above the plant canopy. The latter conditions are
strongly determined by the geometry and density of the plant stand. Thus,
leaf conductance by itself is insufficient to predict transpiration, but it is, in
addition to LAI, the major component that is under biological control.
22.2 Constraints of Utilizing Leaf Conductances in Vegetation Modeling
In this contribution, key components of leaf diffusive conductance will be
summarized for a number of globally important biomes. However, it is clear
from the above that the applicability of these numbers for leaf conductance
in the Major Vegetation Types of the Globe
Ch. Korner
22.1 The Significance of Leaf Conductances in Vegetation Modeling
Water availability is a key determinant of growth and distribution of individual plants as well as vegetation. In turn, plant coverage of landscapes
influences terrestrial water storage, and - by controlling evapotranspiration
- feeds back on the climate and soil moisture regimes. Because of this
interrelation of plant functioning with climate and soils, plant control of
vapor loss is an important component of biosphere as well as global circulation models.
By far the largest fraction of terrestrial evaporative water loss passes
through the microscopic stomata pores of plant leaves. It is estimated that
this pathway accounts for 70% of the evaporative vapor loss in Europe
(Maniak 1988), and similar values may apply to other regions. The degree of
stomatal opening, expressed as the diffusive conductance of leaves for water
vapor (g), is controlled by physiological processes, which themselves respond to environmental conditions such as photon flux density, soil, or
atmospheric moisture. The maximum rate of vapor loss of vegetation for
any given meteorological situation is determined by the maximum diffusivity
of leaves (i.e., the number and geometry of stomatal pores), and the total
amount of leaf area per unit of land area (the leaf area index, LAI). At
any given leaf conductance the most important climatic determinants of
transpiration are the moisture deficit of the atmosphere and the aerodynamic conditions in and above the plant canopy. The latter conditions are
strongly determined by the geometry and density of the plant stand. Thus,
leaf conductance by itself is insufficient to predict transpiration, but it is, in
addition to LAI, the major component that is under biological control.
22.2 Constraints of Utilizing Leaf Conductances in Vegetation Modeling
In this contribution, key components of leaf diffusive conductance will be
summarized for a number of globally important biomes. However, it is clear
from the above that the applicability of these numbers for leaf conductance