CARBON IN THE BIOTA 301 



a residential neighborhood that is a kind of man-made woodland is created. I 

 think, overall, the direction almost everywhere must be one of decrease in 

 biomass. I cannot really speculate on the overall effect on the carbon cycle. 



Mitchell: Recalling Dr. Machta's estimate in the opening session that 

 something of the order of one-quarter of the fossil carbon added to the 

 atmosphere may be going into the biosphere, 1 just made a quick calculation that 

 this represents only about 0.1% increase per year in the total biota carbon 

 reservoir you estimate in your paper. This would be extremely difficult to 

 measure if we want to verify by actual measurement that this is really where 

 some of the fossil atmospheric carbon is going. 



Whittaker: This seems to me almost impossible in terms of method. Under 

 experimental conditions, one can pick up the effect, but in natural communities 

 the difficulties are staggering. A friend in California pointed out to me the 

 possibly happy effects of air pollution in the great valley of California —that air 

 pollution first increases the C0 2 levels and then produces a diffuse canopy that 

 has a ground-glass effect on the light, dispersing it. Both of these, he said, should 

 tend to increase productivity of the farming areas of the Great Valley of 

 California. I though him too sanguine. 



Reiners: Am I correct in surmising from your paper that it is unlikely that 

 terrestrial biomass is increasing and thus serving as a carbon receptor for excess 

 fossil-fuel C0 2 ? 



Whittaker: I think that the cutting of forests is the overwhelmingly 

 dominant influence. 



Richardson: To what extent might it be possible to estimate world net 

 productivity from seasonal changes in atmospheric C0 2 measured at a number 

 of selected stations around the world? These seasonal changes were dramatically 

 evident in the records from the Mauna Loa observatory which were presented 

 earlier in this symposium. 



Whittaker: I have no idea. This seems to be a tenuous kind of extrapolation 

 from such measurements in the few places where they could be made, but all I 

 can say is that it is an interesting idea. I think that no one has tried it. 



Deevey: Note that my own independent estimates from Rodin and 

 Basilevich's data yield the opposite conclusion from yours from the same data, 

 i.e., it is at least arguable that the biota is growing and not diminishing. I want to 

 stress that, even if you are right, the vital effect of clearing a tropical forest stand 

 is to increase, not decrease, the productivity. Substitution of immature for 

 mature systems will normally have this effect, in the short run of course. 



Whittaker: I agree that this is too complex a matter to debate here, but I 

 would observe this: although it is true that individual immature forest stands are 

 growing, at the same time many of these and others are being cut. Considering 

 the manner in which forest cutting is progressing, I myself must believe that it is 

 the cutting which prevails over the growth in the overall average. 



Deevey: If the cutting exceeds the growth, one result is to increase, not to 

 decrease, the productivity. Under reasonable treatment of a cleared forest, the 



