Production and standing crop of litter and humus in a forest exposed to chronic gamma irradiation for twelve years

Continuous exposure since 1961 of an oak-pine forest at Brookhaven National Laboratory to chronic gamma irradiation has shown: (1) progressive reduction in litter production from the first year through 1965; (2) greater litter production in 1973 compared to 1965 at exposure rates below 9 R/day primarily because of the prolific sprouting of the oaks, especially Quercus alba; (3) further reduction in litter production in intermediate zones (14-49 R/day) from 1965 to 1973 as a result of replacement of the forest by a Carex pensylvanica mat; (4) increased litter production in the high exposure zone (125 R/day) in 1973 as a result of colonization by adventive species; (5) reduction in the standing crop of litter by 1973 at the lowest exposure rate studied (3.5 R/day) although in 1965 there was no reduction at exposure rates up to 15 R/day; (6) decline in humus content at 4.6 R/day and above with the standing crop in the Carex zone exceeding that of the shrub and damaged forest zones of lower exposures. Both further losses and partial recovery in the production and storage of organic matter have occurred since 1965. These changes constitute a portion of the long-term response of the forest to chronic disturbance. The pattern of response is the result of ecosystem processes that are still not in equilibrium with the chronic disturbance and which were not predictable from short-term studies, even those spanning as much as 4 yr