FOLIAR NUTRIENTS IN SUGAR MAPLE FORESTS ALONG A REGIONAL POLLUTION-CLIMATE GRADIENT

Stressing agents such as defoliation, adverse climatic conditions, and pollutant deposition have the potential to alter forest nutrition. Several recent instances of sugar maple (Acer saccharum Marsh.) de dine and dieback have been associated with foliar nutrients deficiencies. This study assessed foliar nutrient status and cycling in five sugar maple dominated northern hardwood forests along a Great Lakes pollution-climatic gradient. Concentrations and contents in mid-July foliage and litterfall were determined at each site for N, P, S, Ca, Mg, IS, Al, Fe, Mn, B, Zn, and Cu. Where differences existed among sites in foliar nutrient concentrations, they could be predicted primarily from soil properties. Two notable exceptions were foliar S, which was strongly related to SO4 deposition, and foliar Al, which could be predicted by a combination of soil nutrient cation availability and SO4 deposition. Nutrient content of mid-July foliage and litterfall increased from northwest to southeast along the gradient for N, S, Mg, Al, Fe, B, and Cu. This was the result of an increase in foliage and litterfall biomass, combined in some cases (S, Al, Fe, and B) with increasing foliar nutrient concentrations. Reproductive effort significantly affected total litter return of all nutrients and 43 to 62% of mid-July foliar N, P, K, and S were conserved through retranslocation prior to litterfall. Sugar maple foliar nutrient concentrations for the five sites revealed no obvious nutrient deficiencies or toxicities, and provide a regional baseline against which the effects of long-term pollutant deposition and other stresses can be assessed in the future.