Biophysical Processes and Primary Production 



87 



Temp, "C 

 10 Jul 



-20- 



-4 -2 



-60 



Temp, "C 

 22 Jul 



Temp, "C 

 4 Aug 



FIGURE 3-13. Profiles of air and soil temperature at different times of 

 the year in the moist meadow canopy. Points show measured values of 

 daily mean temperature. Curves give results of simulations. (After Miller 

 et al. 1976, Ng and Miller 1977.) 



Ng and Miller (1975, 1977) presented a model of canopy processes, 

 ground surface heat exchange, and soil heat conduction based on micro- 

 climate and foliage area profiles measured in 1973. The model predicted 

 the seasonal course of soil temperature well, except during a period of 

 snow (Figure 3-13). The simulation indicated that in the Carex-Onco- 

 phorus meadow, evaporation from the wet moss-soil surface can ac- 

 count for over 80% of the latent energy lost with low and ambient foliage 

 area indices (0.5 and 1 .9), but that evaporation can decrease to 40 to 75% 

 of the energy lost with a foliage area index of 4.6. The amount of the 

 decrease depended on the extinction coefficient for turbulent transfer; 

 the coefficients used, 1.0 and 0.5 respectively, were within the range of 

 measured values. With a dry ground surface and foliage area indices of 

 0.5 and 1.9, convection accounted for over 90% of the energy lost from 

 the ground, but at the high foliage area index convectional loss was 77 to 

 84%, depending on the turbulent exchange extinction coefficient (1.0 

 and 0.5, respectively). Under normal or wet conditions with a turbulent 

 exchange extinction coefficient of 0.5, convection added energy to the 

 surface with all foliage area indices. But using an extinction coefficient 

 of 1 .0, convection added energy only with the low and ambient foliage 

 area indices. Using the extinction coefficient of 0.5, both the energy con- 

 ducted into the ground and the depth of thaw decreased with the higher 

 foliage area index. However, the converse occurred with an extinction 

 coefficient of 1.0. These results have the common basis that decreasing 

 the extinction coefficient for turbulent transfer increases the turbulent 

 transfer at the soil surface and increases heat loss due to evaporation and 



