ESTIMATING THE EFFECTS OF CARBON 

 FERTILIZATION ON FOREST COMPOSITION 

 BY ECOSYSTEM SIMULATION 



DANIEL B. BOTKIN,* JAMES F. JANAK,t and JAMES R. WALLISt 

 *School of Forestry, Yale University, New Haven, Connecticut, and 

 tIBM Thomas J. Watson Research Center, Yorktown Heights, New York 



ABSTRACT 



We have used a computer model of a forest ecosystem to investigate the effects of carbon 

 dioxide fertilization on the structure and function of that ecosystem. Simulated fertilization 

 was carried out, assuming only that an increase in C0 2 increased the annual diameter 

 increments of all trees by an equal percentage. The model predicts that this treatment would 

 weight the environment in favor of shade-tolerant, long-lived species and hasten the process 

 of succession. Changes in productivity and biomass would be obscured by these effects and 

 by the stochastic processes of mortality and seedling survival. 



That individual green plants grow better in air enriched with carbon dioxide has 

 been known since the 18th century. The effects of such an enrichment of 

 earth's entire atmosphere on natural terrestrial ecosystems are hard to foresee. 

 Meager knowledge of ecosystems and their innate complexity makes difficult an 

 assessment of the long-term ecological effects of any environmental perturba- 

 tion, but even if knowledge were plentiful, our minds would have difficulty 

 assessing the probable outcome of any complex mechanism, such as an 

 ecosystem, that operates overtime with many feedback loops. What one needs is 

 a tool that faithfully remembers the implications of one's assumptions and 

 faultlessly moves the system through time. It is obvious that computer modeling 

 and Monte Carlo simulation could provide such a tool, but so far few successful 

 ecological applications have been reported. Why is this? Have we been victimized 

 by inappropriate theories? Have we made the wrong hierarchical assumptions? 

 Have we insisted on accurate micro components and hoped that these would 

 automatically interface to give reasonable macro simulations? Probably all have 

 their own themes for the dearth of successful ecosystem simulations, but most 

 will agree that the power of the computer has yet to be realized in ecology. 



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