II. PRIMARY PRODUCTIVITY OF COASTAL MARSH PLANTS 

 A, Productivity of Coastal Environments 



II-A-1 



Westlake, D.F. 1963. Comparisons of plant productivity. Biological 

 Reviews of the Cambridge Philosophical Society 38:385-425. 



This article discusses the principles of comparative productivity 

 and the net primary productivity of different types of plant communities. 

 The author defines primary production as weight of new organic matter 

 created by photosynthesis over a period of time. This is expressed 

 as a rate. Several other pertinent definitions are also provided. 



Ways of adjusting source data to a common form are examined at length, 

 for meaningful comparisons are impossible if this is not done. Source 

 data are published according to a great variety of criteria such as 

 fresh weight, dry weight, oxygen production, and carbon fixation. 

 Standing crop or yield data need correction for omitted parts of the 

 plant. The determination of productivity from changes in biomass may 

 involve corrections for material accumulated from earlier periods and 

 for losses due to death or grazing. Conversions from gross production 

 to net production are usually required when photosynthetic determinations 

 are made. 



Problems raised by the use of different units are discussed, and 

 selected factors are listed for conversions to the recommended units. 

 The basis adopted for comparisons is the maximum average annual net 

 productivity of organic (ash-free) matter that can be attained over 

 a large area. This facilitates the comparison of the productivity of 

 different types of communities by minimizing differences due to local 

 site conditions and weather, and is the most useful measure for 

 general ecological purposes. For some selected examples, the produc- 

 tivity and biomass are expressed in a variety of other ways to facilitate 

 direct comparisons with source data. 



Methods for determining productivity are only discussed insofar 

 as the details affect the comparability of the results. The 

 most productive temperate communities appear to be fertile reed- 

 swamps, which may produce 30 to 45 metric tons per hectare (m.t./ha.) 

 in a year. Coniferous forests and perennial plants under intensive culti- 

 vation may produce 25 to 40 m.t./ha. Deciduous forests, uncultivated herbs 

 and cultivated annual plants are less productive (10 to 25 m.t./ha). 



The phytoplankton of lakes and oceans is relatively poor in terms of 

 productivity, even on fertile sites, with an annual production of only 

 1 to 9 m.t./ha. Values greater than 3 m.t./ha. are achieved only in 

 waters enriched by man's activities or in the tropics. Submerged 

 freshwater macrophytes are no more productive in the temperate region, 

 but may attain 13 to 21 m.t./ha. in warmer climates. Benthic marine 

 plants in shallow waters may produce more; from 25 to 33 m.t./ha. in 



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