86 P. C. Miller et al. 



10 



0.5 1.0 



Absorptance 



25 50 



Leaf Resistance, s cm"' 



FIGURE 3-12. Effect on simulated 

 leaf temperatures on about 10 July 

 (5-day mean) at solar noon of 

 changes in A) leaf absorptance, B) 

 leaf width, C) leaf resistance to water 

 loss at two ambient vapor densities, 

 and D) leaf resistance to water loss at 

 three wind speeds. The standard envi- 

 ronmental conditions used were: total 

 solar irradiance 560 J m'^ s~\ infrared 

 radiation from the sky 280 J m~^ 5"', 

 air temperature 6.0°C, wind speed 

 1.0 m s'^ and vapor density of the air 

 7.9 g m'\ 



Influence of the Canopy on the 

 Soil Thermal Regime 



The moss or soil surface temperature is the interface between the 

 aerial and soil thermal regimes. In natural and modified vegetation cano- 

 pies, thaw depth was shallower with higher foliage areas (Brown et al. 

 1969, Linell 1973, Ng and Miller 1977). In field experiments (Ng and Mil- 

 ler 1977), thaw depth on 1 August decreased 3 cm with an increase in foli- 

 age area index of 1.0 on the control plots. These shallower thaw depths 

 reduce the available minerals and water for the plants, and lower temper- 

 atures of the roots. 



