INTRODUCTION 



The growing interest in dynamic community ecology over the past 20 or so years has 

 provided an increasing volume of data on the productivity, accumulation, and turnover 

 rates of organic matter for a number of terrestrial ecosystems. Although methods of 

 study vary and most reports give only gross estimates of the parameters, the values 

 reported are of such relative magnitude for each ecosystem that they fall rather consist- 

 ently into a rational global pattern (Rodin and Basilevich 1968). Most of the available 

 information on Temperate Zone deserts is from Central Asia. In North America, Chew and 

 Chew (1965) studied the productivity of a warm desert in southeastern Arizona, but their 

 data on accumulated organic matter are incomplete, except for that of one species. 

 Pearson (1965) gives estimates of biomass above and below the ground in his study of 

 productivity of a cold semidesert steppe in eastern Idaho. In an investigation of nitro- 

 gen cycling, Bjerregaard (1971) determined the biomass of two salt-desert shrub communi- 

 ties in northern Utah. 



Because of sampling problems, the underground portion is the least known part of 

 terrestrial ecosystems, especially in communities of woody perennials, where much of 

 the plant material is contained in coarse roots concentrated in small areas near trees 

 or shrubs. We present here data obtained from a study made with another objective (soil 

 moisture movement) in mind, and use them to show the amount of accumulated biomass 

 (including dead material), and its three-dimensional distribution in a cold desert shrub 

 community in the eastern part of the Great Basin. Earlier studies of the response of 

 vegetation to grazing were conducted in the same area; the productivity data from these 

 studies, in conjunction with our data, enable us to estimate a turnover rate for organic 

 material on this site. 



The mass of accumulated organic matter is at its annual minimum at the end of win- 

 ter, just as the growing season starts. Because this is a desert of woody perennial 

 plants, where the minimum of organic matter reserve is several times greater than the 

 annual increment and the breakdown of litter is slow, the magnitude of the minimum 

 probably varies little from year to year. Although the annual increment does vary 

 considerably, being dependent upon a variable annual precipitation (Hutchings and 

 Stewart 1953), the rate of decomposition, which is also dependent on moisture, varies 

 similarly. From the known history of the study area, we assume it to be near a steady 

 state of productivity and decay. 



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