Factors Affecting Rates of Production

Abstract

We know that various environmental factors affect photosynthetic efficiency of forest trees and that such relationships are discussed in many textbooks of ecology and physiology. In previous chapters we have described how the dry matter production of forests is affected by various environmental factors and by the management practices of foresters. However dry matter production is not only dependent on rates of photosynthesis; many intermediate processes are involved. Monsi (1960) has described these production processes schematically. Supposing, for simplicity, that the mean photosynthetic rate (a) and mean respiration rate by leaves (r) and non-photosynthetic tissues (r’) do not change in a given time period, net production (Pn) may be expressed as:

$$\text{Pn} = \text{F(a - r)} - \text{C}\text{.r}'\,\, \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(6.1)

where F is the amount of leaves and C the amount of non-photosynthetic tissue (either for individual plants or for plant communities occupying a unit ground area). Using subscripts to indicate values of Pn, F, and C at successive points in time, t₀, t₁, t₂, etc., then at time 0:

$$\text{Pn}_\text{0} = \text{F}_\text{0} \,\text{(a - r)} - \text{C}\text{.r}'\,\, \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(6.2)

Pn₀ is distributed to make additional photosynthetic or non-photosynthetic tissues and added to F₀ and C₀, thus:

$$\text{Pn}_\text{0} = \Delta \text{F}_\text{0} \, + \Delta \text{C}_0 \,\, \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(6.3)

and

$$\text{F}_\text{1} = \text{F}_\text{0} \, + \Delta \text{F}_0 \,\text{and}\,\text{C}_\text{1} = \text{C}_\text{0} \, + \Delta \text{C}_0 \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(6.4)

at time t₁

$$\text{Pn}_\text{1} = \text{F}_\text{1} \,\text{(a - r)}\, - \text{C}_\text{1} .\text{r}'\,\, \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(6.5)

and so on.