Seasonal variation of the seed bank of Medicago minima and Erodium cicutarium as related to grazing history and presence of shrubs in central Argentina

Medicago minima (L.) Grufberg and Erodium cicutarium (L.) L'Herit are very abundant on the rangelands of central semi-arid Argentina, especially. on wet springs. Available information on these species deals with their ecophysiology, demographic response to grazing, nutritive value, etc., but no information within the region has been detected on their seed bank dynamics and dormant status of buried seeds. The main objective of this work was to study the seasonal variation of the seed bank of these species as related to shrub and grazing influence. Dormancy states and viability of buried seeds were also studied. Results indicate that the seed bank is abundant, especially in the case of M. minima, and it seems to be more abundant in the grazed area than in the ungrazed area. The seed bank showed low seasonal variation and shrubs seem to have only minor effects. Two simultaneous dormancy states were detected in both species and all seeds tested for dormancy resulted viable. (C) 1999 Academic Press.