Effects of soil fumigation and seeding regimes on secondary succession in a semiarid shrubland

In order to ascertain the degree to which disturbance and subsequent recove ry of belowground biotic components (mycorrhizal and decomposer systems) in fluence successional dynamics, a portion of semiarid shrubland in northwest Colorado was mechanically disturbed in 1984. Two treatments, soil fumigati on (fumigated with methyl bromide and not fumigated) and seeding (early-ser al species, late-seral species, and not seeded) were imposed on 500 m(2) pl ots in each of four replications. Aboveground annual production by species, and decomposition rates were measured in 1991, 7 years after the initial d isturbance and treatments. Mycorrhizal infection potential had been previou sly measured at this site from 1984-1988. Seeding to late-seral species res ulted in greater production rates (and greater community composition) of la te-seral species, whereas seeding to early-seral species had only a minor e ffect when compared to unseeded plots 7 years after disturbance. Fumigation slowed the rate of succession on unseeded plots, primarily by decreased pr oduction of perennial grasses. Mycorrhizal infection potential, initially g reatly reduced by the disturbance and by fumigation, recovered to near-back ground levels on unfumigated plots but not on fumigated plots after 4 years . Decomposition experiments suggest that seeding may have facilitated recov ery of the decomposer system after initial disturbance and fumigation. Our results suggest that the redevelopment of soil biotic communities following disturbance has a significant impact on successional dynamics, particularl y the replacement of early-seral annuals by mid-seral perennial grasses.