CANOPY TREE SOIL INTERACTIONS WITHIN TEMPERATE FORESTS - SPECIES EFFECTS ON PH AND CATIONS

We quantified soil acidity and exchangeable cations in the forest floo r and upper 7.5 cm of mineral soil beneath the canopies of individual trees of six different species in a mixed-species forest in northweste rn Connecticut. Soil pH decreased in a sequence starting with sugar ma ple (Acer saccharum) > white ash (Fraxinus americana) > red maple (Ace r rubrum) > beech (Fagus grandifolia) > red oak (Quercus rubra) > east ern hemlock (Tsuga canadensis). The differences among species were lar gest in the forest Boor and the top 7.5 cm of mineral soil. Exchangeab le Ca and Mg in the 0-7.5 cm mineral soil layer were significantly hig her beneath sugar maple than all other species, with the exception of white ash. There were negligible differences among species in the quan tity of exchangeable Ca and Mg in the forest floor. In the 0-7.5 cm mi neral soil layer, exchangeable Ca was positively correlated with the c ontent of unweathered Ca in the parent material, but the relationship differed among species. There was a large increase in exchangeable Ca in the soils beneath sugar maple but a negligible increase in the soil s beneath hemlock and red maple. Exchangeable Al and Fe were highest b eneath hemlock and lowest beneath sugar maple. The differences in pH a nd exchangeable cations between sugar maple and hemlock are likely due to interspecific differences in the introduction of acidity (e.g., or ganic acids) and Ca uptake and allocation. Observing an association be tween tree species and specific soil chemical properties within mixed- species stands implies that changes in the distribution and abundance of tree species alters the spatial and temporal pattern of soil acidit y and cation cycling in this forest.