CARBON FERTILIZATION EFFECTS IN A SIMULATED ECOSYSTEM 329 



We have recently reported elsewhere a computer simulation that successfully 

 reproduces the population dynamics of trees in a forest. The simulation has a 

 basis that makes it an appropriate tool for considering the effects of various 

 perturbations on natural communities (Botkin, Janak, and Wallis, 1972a and 

 1972b). This simulation was constructed with a biological orientation, reflecting 

 currently available information and assumptions about terrestrial communities. 

 We tried to create a model that would be dynamic in the sense that changes in its 

 state would be the result of its current state plus random components. In such a 

 model the cumulative effects of perturbations are not necessarily obvious 

 beforehand nor analytically predictable from the initial conditions. 



We make no claims that this simulation provides a definitive treatment of a 

 forest ecosystem. We claim only that it is a reasonable approximation of current 

 understanding of the population dynamics of forest tree species and that it 

 successfully reproduces the general dynamic characteristics of a forest. Here we 

 shall use the simulation in an attempt to assess: what carbon dioxide fertilization 

 of a forest would do to the structure and function of that ecosystem; how much 

 fertilization would be necessary to produce significant changes; and what these 

 changes would imply for the global cycle of carbon. After the fact, our results 

 appear somewhat obvious, but we present them here because we believe that 

 they do show up some interesting deficiencies in knowledge. 



Before considering our simulated experiments, we believe that it is necessary 

 to understand the basis of the model, of which a brief description follows. For a 

 more complete discussion of the assumptions and limitations of the model, the 

 reader is referred to Botkin, Janak, and Wallis (1972a). 



DESCRIPTION OF THE MODEL 



The simulation was originally designed for use in the Hubbard Brook 

 Ecosystem Study in the White Mountains of New Hampshire. In its present 

 version it simulates forests typical of that study area and of northern New 

 England. However the underlying concepts are general, and in theory the 

 simulation could be extended to many terrestrial ecosystems. 



In the simulation, tree species* are defined by a few general characteristics: a 

 maximum age, maximum diameter, and maximum height; a relationship between 



*Sugar maple (Acer saccbarum), beech (Fagns grandifolia) , yellow birch (Betula 

 allegbaniensis), white ash (Fraxinus americana), mountain maple (Acer spicatum), striped 

 maple (Acer pensylvanicum), pin cherry (Prunus pensylvanica), chokecherry (Prunus 

 virginiana), balsam fir (Abies balsamea), red spruce (Picea rubens), white birch (Betula 

 papyrifera), mountain ash (Sorbus americana), and red maple (Acer rabrum) (nomenclature 

 follows Gleason, 1968). 



