EVAPORATION PATTERNS IN FORESTS OF DIFFERENT AGES, SITE CONDITIONS, AND PRODUCTIVITY LEVELS

Abstract

The paper analyzes the factors behind evaporation from a forest: foliage and solar irradiance. The patterns of foliage formation and its changes with age in forests of varying productivity are demonstrated. The limiting factor for stand growth and development in each type of forest is the energy resources available. The average radiation balance of a region being given, the stand productivity depends on the characteristics of the locality, which influence soil fertility and predetermine the forest type. The southwards enhancement of the quality class of a forest type with a rise in the radiation balance is associated with the growing share of foliage and intensification of biochemical processes. The share of foliage mass in the total biomass of the tree stand depends on the forest site conditions, quality class, and energy supply. Previously designed techniques have been applied to calculate age-related patterns of evaporation from forest sites of varying habitat conditions and productivity in middle and southern taiga. As the radiation balance grows, physical evaporation from forest areas increases, and the growing share of foliage in the tree stand’s total biomass enlarges transpiration by the stand in every forest type and quality class. Alteration of site conditions entails a change in the age-related pattern of evaporation and transpiration by the stand. Enhancement of site conditions and quality characteristics leads to an increase in evaporation in young and middle-aged forests, however in mature and over-mature forests this trend may be broken. The greatest evaporation and transpiration by the stand are observed at an age when current biomass increment is the highest and the amount of foliage is at maximum. According to our calculations, the age of maximum annual total evaporation and transpiration varies from 50 to 100 years depending on the forest site conditions