Forage Quality 



As discussed earlier, annual variations in the length of 

 time plants remain green and succulent, providing high quality 

 forage, appeared to be a major factor influencing mule deer 

 population dynamics on our study area. Both our observations 

 and those of Blaisdell (1958) indicated that high forage 

 production was correlated with delayed maturation, hence the 

 apparent relationship between population dynamics and forage 

 quantity. However, delayed maturation as a result of cool 

 spring temperatures also provided a longer period during 

 summer and autumn that high quality forage was available, 

 providing adequate forage for lactation through summer and fat 

 accumulation prior to winter. Late summer and early autumn 

 rains that resulted in an autumn green-up of grasses during 

 1962, 1977, 1985, and 1986 provided a longer period of high 

 quality forage and resulted in high fawn production and 

 survival during 1963, 1978, 1986, and 1987. High total 

 precipitation for the 10 months prior to the growing season 

 also influenced fawn production and survival as long as above 

 average growing season temperatures did not result in early 

 plant maturation. 



We agree with Klein (1985) that maximization of selective 

 feeding by cervids is most likely to occur in mountainous 

 regions where wide variability in exposure, slope, and 

 altitude create a diversity of microclimatic influences. The 

 distribution, habitat use, and home range patterns of deer on 

 our study area indicated similar conclusions. Deer, 

 especially females with fawns, preferred the most 

 topographically and vegetationally diverse areas and were able 

 to utilize smaller home ranges in those areas. 



In contrast to mountainous areas, however, the 

 elevational gradient on our study area was relatively small. 

 In northern mountainous areas, green forage is always 

 available until autumn frosts, even during dry years. On our 

 study area, forage maturation and desiccation was delayed 

 somewhat on steep north- and east-facing slopes during average 

 to good years, but during extremely dry years, most forage 

 became desiccated on even those sites by early August. For 

 example, the leaves of deciduous shrubs remained green during 

 most years until the first frost or early September, but 

 deciduous shrubs dried out and the leaves turned colors and 

 dropped by late July in 1961 and 1984, even on north-facing 

 slopes. After that time, even non-productive adult deer were 

 probably on no better than maintenance diets for the remainder 

 of the year. 



All of our data indicated that the length of time that 

 high quality, green, succulent forage was available had a 

 major impact on fawn survival and thereby population dynamics. 



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