INTRODUCTION 



Annual differences in plant growth and production are among the most commonly 

 observed phenomena on our native rangelands. In addition, knowledge of growth and 

 production are fundamental to understanding the dynamics of the grassland ecosystem. 

 Despite their conspicuousness and importance, these phenomena have not been documented 

 for all range types. Mountain grasslands of western Montana are among those areas where 

 information is generally lacking on yearly variations in plant development and herbage 

 yield. 



During a continuing study of the relation between plant growth and weather, 1 

 accumulated data on variations in development and yield at four different mountain grass- 

 land sites. A summary of these data is presented here for those interested in mountain 

 grassland vegetation. Resource managers should find this summary useful for judging 

 the amount of year-to-year variability in range readiness for grazing and the varia- 

 bility in grazing capacity that can be expected to occur naturally on such areas. 



1 



