Table 3.5. Abundance (number of plants/2 frequency) of yellow sweetclover 

 in 310 4x10 dm plots on 31 sites, 1977-1986. 



First Second 



Year Year Avg. Weight 3 



Year Plants Plants (g) per plant kg/ha 



1977 11/1.9 0/0 



1978 3227/44.2 21/3.5 



1979 0/0 1407/38.1 



1980 90/3.5 0/0 



1981 2582/54.2 9/2.9 



1982 2563/53.9 291/26.5 



1983 544/22.9 769/46.8 



1984 3205/35.5 21/3.2 



1985 46/3.2 0/0 



1986 3695/62.6 108/11.9 

 a Average weight (g) per plant taken from separate clipped plots, 



same period. Although this often was the case, cool 

 temperatures also occurred in the absence of precipitation. 

 Thus, mean temperature for April and May was significantly 

 negatively correlated with forb production, but precipitation 

 during those months was not (Table 3.6). The negative 

 relationship between mean growing season temperature and 

 forage production appeared to be independent of a correlation 

 with precipitation. 



Multiple regression models incorporating both temperature 

 and precipitation variables were computed for the period 1976- 

 1982, when production of all forage classes was measured 

 (Table 3.7). Mean temperature during May and precipitation 

 during the previous July-April period together explained 91.5% 

 of the annual variation in forb yield (R 2 = 0.915, F = 21.55, 

 P = 0.009). Stepwise procedures indicated that both variables 

 were significantly related to forb yield; mean May temperature 

 explained 73% of the variation and an additional 18.5% was 

 explained by July-April precipitation. Production of 3 shrub 

 species was best predicted by precipitation during July-May 



59 



