Woody biomass and litter production of fertilized grey alder plantations on a low-humified peat bog

Abstract

Production of woody biomass and litter by planted grey alder stands grown on a sphagnum peat bog in central Sweden were studied. The stands were treated either by daily nutrient irrigation, including nitrogen, during the growing season (IL) or solid fertilization with all essential nutrients except nitrogen, once every second year (F). The above-ground woody biomass and litter production was fairly similar in the two treatments each year, while the annual woody biomass production increased during the study period, reaching 10–11 t dm ha −1 year −1 after 7 years. The leaf litter production also increased but levelled off at 3–4 t dm ha −1 year −1 after 5–7 years. In both treatments about 100 kg N ha −1 year −1 was returned to the soil through litterfall. The IL stands had somewhat less accumulated woody biomass during the first 4 years but thereafter it was higher than in the F stands, probably because of larger microbial immobilization of nutrients and by competition for nutrients between weeds and alders in the IL stands during the initial years. The high production of the F stands without nitrogen fertilization indicated an effective N 2-fixation by the introduced Frankia strains in the tree bacteria symbiosis. Water supply seemed to be limiting on the drained peat bog in non-irrigated stands during periods when precipitation was low. This may have caused the early peaks of litterfall during dry summers and also the lower woody biomass productions in the next 2 years.