Fluctuations in Miserotoxin Concentration of Timber Milkvetch on Rangelands in British Columbia

Abstract

The variation in miserotoxin concentration (percent dry weight) of timber milkvetch (Astragalus miser var. serotinus) was ascertained for 19 sites throughout British Columbia. Determinations were based on recently developed methods of micro-isolation and derivatization of miserotoxin from fresh-frozen timber milkvetch samples. With the exception of one site, timber milkvetch located in fescue grassland areas yielded the highest miserotoxin values (5.8 to 7.3%); whereas the lowest peaks (3.1 to 4.3%) were recorded in the medium-canopied forests of the Douglasfir-pinegrass community. Subalpine, savannah, parkland, and semiopen areas of the montane forest exhibited intermediate miserotoxin maxima (4.3 to 5.8%). The data for 1973 suggest that grazing should be avoided in the fescue grasslands in spring and minimized in exposed forest areas.