Forage Plant Production, Abundance, Vigor, and Use 



Forage Production 



The characteristically wide fluctuations in weather- 

 climatic conditions on the study area were reflected in wide 

 variation in plant species production, abundance, and quality, 

 within and among years . Measurements of standing current 

 growth of f orbs , grasses, and shrubs during July, 1976-1986 

 (Table 3.4), show that annual production of forbs on 2 sites 

 within the sagebrush-grassland type varied nearly 16-fold 

 between low and high years, while production of grasses varied 

 by a factor of about 4.5. Current annual growth production of 

 3 shrub species in the Douglas fir- juniper type varied 5.3- 

 fold between years of high and low production within a 

 shorter, 7-year period that did not include the year of lowest 

 forb growth. Annual production of yellow sweet-clover, a 

 biennial forb highly preferred as forage by mule deer varied 

 even more than forbs in general (Table 3.5). 



To further evaluate fluctuations in forage production and 

 estimate annual production and trends for years prior to 1976, 

 a series of regressions relating production to climatic 

 factors were computed. Factors included as independent 

 variables were based on studies by Rogler and Haas (1947), 

 Blaisdell (1958), Dahl (1963), Shiflet and Dietz (1974), Cable 

 (1975), and Smoliak (1986). Ideally, available soil moisture, 

 precipitation during the growing season, and 

 evapotranspiration data were most likely to relate to forage 

 production. Lacking direct measurements of available soil 

 moisture and evapotranspiration for the study area, 

 precipitation prior to and during the growing season and 

 temperature during the growing season seemed to best predict 

 forage production (Blaisdell 1958, and Smoliak 1986). 

 Precipitation prior to and during the growing season 

 influenced available soil moisture, and temperature during the 

 growing season influenced evapotranspiration. 



Precipitation and temperature variables most closely 

 correlated with production on the area are listed in Table 

 3.6. Many combinations of precipitation prior to and during 

 the growing season (including some not listed in Table 3.6) 

 provided high positive correlations with forb and shrub 

 production. Precipitation during April and May was the only 

 variable that provided a significant correlation with yield of 

 grasses. Mean monthly temperature during the growing season 

 was significantly negatively correlated with forb yield and a 

 combined f orb-shrub yield index. 



Cooler temperatures during April and May might be 

 expected to correlate with higher precipitation during the 



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