Biophysical Processes 

 and Primary Production 



p. C. Miller, P. J. Webber, 



W. C. Oechel, and L. L. Tieszen 



INTRODUCTION 



During most of the year the arctic tundra is covered with snow, and 

 the exchange of heat at the earth's surface through radiation, convection 

 and evaporation involves only physical components of the environment. 

 However, during the short snow-free period the vegetation becomes a 

 significant exchange surface. The vegetation influences the partitioning 

 of incoming energy into evaporation, convection and soil heat conduc- 

 tion. The vegetation also accumulates the biomass on which the plants 

 themselves and the other ecosystem components depend for energy. This 

 chapter discusses the rates of primary production, the standing crop, and 

 the partitioning of incoming energy by the vegetation. The interactions 

 between diverse environmental factors and specific canopy and plant 

 properties affecting plant temperatures are integrated in the energy 

 budget equation (Gates 1962, 1965, Parkhurst and Loucks 1972, and 

 others): 



Q^ + Oa = d+G + H + LE + M 



where Q„ = incoming shortwave radiation absorbed by the plant 

 da = longwave radiation absorbed by the plant 

 d = longwave radiation emitted by the plant 

 G = net heat flux into the soil or moss layer 

 H = heat exchanged by convection 

 LE = evaporative loss of energy by transpiration from vascular 

 plants or the evaporative loss of energy from moss sur- 

 faces 

 M = metabolic term to account for energy used in photosyn- 

 thesis or produced in respiration. 



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