Effects of rainfall variability and gopher disturbance on serpentine annual grassland dynamics

Studied the dynamics of a serpentine annual grassland in N California in relation to disturbance by pocket gophers Thomomys bottae and interannual variation in rainfall over 1982-1988. Annual rainfall varied 3-fold and plant community dynamics were strongly affected by this. In particular, Plantago erecta decreased and Lasthenia californica increased in abundance with increasing rainfall. Abnormally high rainfall in 1982-1984 allowed the buildup of populations of Bromus mollis, the only nonnative species that invades the serpentine significantly. B. mollis was, however, subsequently virtually eliminated from the serpentine grassland by 2 consecutive years of severe drought. Invasion of B. mollis was found only on gopher mounds formed in 1983. In subsequent years recolonization of gopher mounds was predominantly by other species, in particular Lotus subpinnatus. Interannual variability in species abundances was most apparent on disturbed microsites. -from Authors