HERBAGE PRODUCTION 



Production of vegetation differed between exposures and fluctuated considerably 

 over the years. Although production was usually greater on the northeast exposures, 

 the magnitude of this difference varied with both elevation and year. Over the 5-year 

 study, the southwest exposure produced only 58 percent as much herbage as the northeast 

 exposure at 7,100-ft. elevation, whereas at 8,200 ft., it produced 90 percent as much 

 herbage as the northeast exposure. Composition of this vegetation also differed between 

 exposures, but again this difference was not consistent between elevations. At the 

 lower elevation, graminoids formed 58 percent of the total production on the southwest 

 exposure and 26 percent on the northeast exposure. At the upper elevation, these 

 proportions were reversed; graminoids formed 36 percent of the vegetation on the south- 

 west exposure and 58 percent on the northeast exposure. 



Herbage production generally fluctuated more between years on northeast than on 

 southwest exposures. Total production on the northeast exposure at 7,100-ft. elevation 

 averaged 1,246 lb. /acre with a coefficient of variation (C) of 26 percent; at 8,200-ft. 

 elevation, it averaged 1,127 lb. /acre with a C of 25 percent. However, on southwest 

 exposures, total production at 7,100 ft. averaged 724 lb. /acre with a C of only 11 per- 

 cent; at 8,200-ft. elevation, production averaged 1,021 lb. /acre with a C of only 

 16 percent. The forbs were primarily responsible for this greater variation in total 

 production on the northeast exposures; the C for forbs averaged 36 percent on the two 

 northeast exposures, and only 17 percent on the two southwest exposures. Variability of 

 graminoid production over the 5 years was about the same on both exposures and at both 

 elevations (C ~ 20 percent). 



The amount of variation in production of individual species at the two lower 

 elevation areas is shown in table 5. These data also exemplify production differences 

 between exposures, which were on facing slopes within 200 yards of each other. Relative 

 production of most species fluctuated considerably more between years than did produc- 

 tion by vegetation classes. This finding supports Blaisdell's (1958) conclusions that 

 (a) individual species vary greatly in their response to the same environmental factors 

 and (b) increased yield of one can compensate for decreased yield of another and thus 

 dampen oscillations in total production. The great difference between years in relative 

 amounts of minor species (those that contribute little to overall production) is prob- 

 ably the result of sampling inadequacies. 



Since 5 years of both production and weather records were available from all four 

 areas, I had an opportunity to relate weather variations to yearly variations in plant 

 production. 1 assumed at the outset that differences in productive capacity existed 

 between the four areas, irrespective of yearly variations in weather. These area dif- 

 ferences were discounted prior to analyses for weather effects. Production for an area 



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