Application of slow release fertiliser to small (0.5x1 m) plots within a serpentine annual grassland community led to significant increases in above-ground biomass and a shift in species relative abundances. In fertilised plots the native forb species which usually dominate the grassland were almost totally replaced by grasses. In the years following initial fertiliser application, a heavy mulch formed from the previous year's grass growth allowed establishment of grass species such as Bromus mollis but significantly reduced forb establishment. Gopher disturbance of fertilised plots in the second and third years of the experiment effectively removed the grass mulch and allowed re-establishment of forb species.

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We present a computer model which simulates population processes and spatial patterning in response to gopher disturbance in an annual grassland community. The model includes the processes of seed production, dispersal, germination and seedling survival of four main grassland species. Runs show that soil disturbance by gophers affects both short-term spatial patterning and long-term species composition. The main determinant of species behaviour is their relative seed dispersal distances, and the model is relatively insensitive to initial species distribution or abundances. The model adequately simulated short-term community patterning, and provided predictions of long-term dynamics which can now be tested using longer-term field experiments.

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