MANAGEMENT IMPLICATIONS 



Range managers generally rely upon vegetation and soil readiness indicators to 

 decide when grazing can safely begin in the spring or early summer. Two common indica- 

 tors of vegetation readiness on mountain grasslands in Montana are Delphinium hiootor 

 in full bloom and appearance of Festuaa idahoensis flower stalks (USDA Forest Serv. 

 1969). IVlien these indicators were applied to this study, the date of vegetation readi- 

 ness for grazing was found to differ as much as 26 days during the 5 years. Weather 

 conditions were not extreme during this period; a greater difference will likely occur 

 over a longer time. However, in 2 out of 3 years, vegetation should be ready to graze 

 within 11 days of the average date of readiness, judging from the variability 

 (a = 11.2) in date of readiness over the 5 years studied. 



Although the lag in plant development attributable to each 1,000-ft. rise in 

 elevation is generally considered to be about 10 days (Hopkins' Bioclimatic Law), the 

 lag apparently can be much greater in some of our mountain areas. In this study, the 

 lag in plant development (and consequently in vegetation readiness for grazing) was 

 18 days/1 , 000-ft . rise in elevation. We can also expect a lag of almost 1 week in 

 vegetation readiness on north exposures compared to south exposures. 



Knowing how much herbage production is likely to vary from year to year assists 

 the range manager (a) in establishing grazing capacities and (b) in anticipating 

 possible yearly adjustments in stocking. This study shows that herbage production 

 differs much more between years on north exposures than on south exposures. Over this 

 one 5-year period, more than twice as much vegetation was produced on northeast exposures 

 during the high year than during the low year; during this same period, only one-third 

 again as much vegetation was produced on southwest exposures during the high year than 

 the low. Generally, production of forbs varies more between years than production of 

 grasses. In 2 out of 3 years, total herbage production on northeast slopes can be 

 expected to be within 26 percent and that on southwest slopes to be within 14 percent 

 of their respective mean productions. 



Regression equations developed in this study for predicting production based upon 

 weather data are primarily of theoretical value. The r'='"ource manager seldom has 

 access to these types of weather data collected on mountain rangelands. However, both 

 the positive relationship established between production and May precipitation and the 

 negative relationship between production and maximum temperatures in June and July have 

 practical significance. In years when May precipitation is above normal and June and 

 July daytime temperatures are below normal, above-average herbage production can be 

 expected. Conversely, when May precipitation is below normal and June and July 

 temperatures are above normal, below-average herbage production can be expected. 



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