282 WHITTAKER AND LIKENS 



the model for the earth's surface. We, as well as others, have used the first 

 approach. 80 82 The second approach was developed for productivity of land 

 vegetation by Lieth. 34 



ESTIMATION OF PLANT PRODUCTION BY ECOSYSTEM TYPES 



World estimation by ecosystem types depends on knowledge of the total 

 area of each type. For land communities, ecosystem types are likely to be the 

 formation types of plant geographers, or biome types, but for the seas a 

 different breakdown into open ocean, continental shelves, upwelling and 

 estuarine areas, etc. is appropriate. Obtaining geographic areas of the formation 

 types on land is not simple. Formations, or structural types of vegetation, 

 intergrade continuously; consistent classification is difficult both because of this 

 continuity and because of the diversity of types and lack of correspondence of 

 some of the types between Southern and Northern Hemispheres. However, an 

 inventory of areas of formations was published by Vahl and Humlum; 74 and 

 both Lieth and we have used also planimetering of maps, data of the Food 

 and Agriculture Organization (FAO), i and other sources, to obtain the areas 

 shown in the first columns of Tables 1 and 2 (compare also Refs. 25, 40, 66). 



Given the areas of ecosystem types, it is next necessary to obtain mean 

 productivities and biomasses of these. A wide range of Western research results, 

 which Lieth summarized 33 ' 34 (see also Refs. 2, 42, 44, 79) and which 

 we compiled since that time, has been supplemented by Rodin and 

 Bazilevich's 7 summaries of Russian work. Other sources have been used for 

 marine (Refs. 10, 29, 51, 55, 63, 64, 71, 72) and freshwater (Refs, 35, 56, 77, 

 78) productivity. There is much disparity in the information available on 

 different ecosystem types; our data for temperate forests are not bad, those for 

 other temperate and arctic communities are reasonable, those for tropical 

 communities are very meager. Both aquatic and terrestrial production measure- 

 ments are subject to intrinsic difficulties of technique; but systematic sources of 

 error may be more vexing, and the estimates consequently less secure, for 

 aquatic communities than for terrestrial ones. To obtain the means in columns 3 

 and 7 of Table 1, we have averaged sets of reported values when these seemed 

 adequate, but in other cases (e.g., tropical forests, savanna, desert scrub) the 

 "mean" is a subjectively chosen intermediate value based on very few 

 measurements. Reliability of means is affected also by exceedingly wide 

 dispersions in the values for some ecosystem types (particularly lake and stream, 

 algal bed and reef, and estuarine communities). It is important that values be 

 based on the full range of conditions of an ecosystem type and not only on the 

 high productivities in more favorable conditions. 



The estimates of world production and biomass are given in Table 1, 

 columns 4 and 8. The marine production total represents the convergent 

 estimates of our earlier table, 80 ' 82 Ryther, 64 and Koblenz-Mishke, Vokovinsky, 

 and Kabanova, 25 ' although Riley 55 and Bunt 10 have suggested these estimates 



