The Influence of the Overstory, Understory and Upper Soil Horizons on the Fluxes of some Ions in a Mixed Deciduous Forest

1989

S. 185-197

2 Abb., 32 Lit. Ang.

Unselbständiges Werk

200088076

Chemical fluxes were measured in precipitation passing through the overstory, understory and upper soil horizon within an aspen-birch forest in Ontario, for ten rain events occurring between May and August 1985. Analysis of mean event chemical fluxes showed that the dominant control on nutrient transfers through aspen systems was that exerted by the overstory. Nutrient transfers through the birch overstory and hazal understory canopy were of a similar magnitude. Hydrochemical changes through the understory below aspen were of the same general types as those occurring within the overstory but only about one-third as large. Overstory throughfall generally contributed a much larger solute load than stemflow, ranging, on average for all ions, from four times larger (for largetooth aspen) to 130 times larger (for trembling aspen). Understory stemflow contributed about six times more solutes than understory throughfall (on average for all ions). The dominance of throughfall in overstories and of stemflow in understories, may be explained by a larger stem area index for understory stems compared with that of tree trunks. Chemical inputs to the mineral B horizons of the soil are controlled by the frequency of heavy rains and by chemical changes in, and withdrawals from, the upper soil during smaller precipitation events.