Predicting peak standing crop on annual range using weather variables

Abstract

Wide yearly fluctuations in peak standing crop on California annual-type range are largely explained by temperature and precipitation patterns. The objective of this study is to improve the predictability of functions relating weather patterns and peak standing crop by including degree-days, dry periods, evaporation, season start dates, and lengths and precipitation as independent variables. Peak standing crop was regressed on these independent variables for the University of California Hopland Field Station (HFS) and San Joaquin Experimental Range (SJER). Fall and winter precipitation, winter degree-days, and longest winter dry period were related to peak standing crop at HFS (R2=0.61). Spring precipitation, growing season degree-days, winter evaporation, and winter and spring start dates were related to peak standing crop at SJER (R2=.72). The relationship of peak standing crop to accumulated precipitation on 20 November using 33 years of data (r2=0.34) was weaker than previously reported for the first 16 years (r2=0.49). This study suggests that timely prediction of peak standing crop may be possible at HFS but more difficult at SJER.