Biophysical Processes and Primary Production 



81 



1.4 - 



1.2 



0.6 - 



0.4 



FIGURE 3-8. Seasonal progression of total foliage area 

 index (live plus dead, Af) and the fraction of incoming 

 beam irradiance intercepted by the canopy (o) and by a 

 unit foliage area (mj. 



age area decreased because of increased self-shading (Figure 3-8). On 21 

 June, when solar irradiance was potentially the greatest, the fraction of 

 incoming radiation intercepted by live leaves in the Carex-Oncophorus 

 meadow was almost zero because of the small foliage area index, but the 

 irradiance per unit foliage area was large. The irradiance per unit foliage 

 area decreased dramatically during the season when the standing dead 

 material was absent, but less dramatically when a constant standing crop 



2 4 6 



Foliage Area Index 



FIGURE 3-9. Ratio of inter- 

 cepted to incoming beam ir- 

 radiance per unit ground sur- 

 face ( — ) and per unit of foli- 

 age surface ( — ) at three 

 solar altitudes (fi) with differ- 

 ent foliage area indices. 



