CARBON IN THE BIOTA 



285 



year l per millimeter of precipitation. Paterson 8 ' 9 has employed formulas 

 using several climatic variables (mean temperature of the warmest month, range 

 between warmest and coldest months, precipitation amount, length of growing 

 season, and insolation). Rosenzweig has shown an effective, logarithmic 

 relation between net primary production and actual evapotranspiration: log 

 NAAP = (1.66 ±0.27) log AE - (1.66 ± 0.07), in which NAAP is net annual 

 aboveground productivity in grams per square meter per year, AE is annual 

 actual evapotranspiration in millimeters, and 5% confidence limits are given. 

 Russian work (Refs. 3, 4, 11, 16) has related production to the ratio of radiation 

 intensity and the amount of heat needed to evaporate the annual precipitation. 

 It is not difficult to establish a variety of such correlations, but none of these has 

 been applied to estimation of world production. 



To make possible such estimation, Lieth 34 has simplified the variables to the 

 two that seem most critical and are most widely available in climatic 

 data — mean annual temperature and mean annual precipitation. Production 

 data are plotted in relation to these variables, as shown in Figs. 1 and 2, and 

 curves are fitted to the data. The equations for these curves are then applied to 

 climatic data to give two production estimates for each station; of the two the 

 lower is chosen as the better estimate by the principle of limiting factors. This 

 technique of prediction may not please the physical scientists among you. It is 

 an approach governed by feasibility, using the curves fitted to dispersed data to 

 average out the many factors that affect productivity but cannot be used for the 



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2000 



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 O 



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 a. 



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10 



20 



30 



TEMPERATURE. °C 

 Fig. 1 Annual dry -matter productivity vs. mean annual temperature. 34 



