Red spruce stands downwind from a coal-burning power generator: tree-ring analysis

Abstract

Tree rings of red spruce (Picearubens Sarg.) in uneven-aged forest stands downwind of an SO2, source (a coal-burning power generator) were analyzed in terms of spatial and temporal trends for bole increments and elemental concentrations (Al, Ca, Mg, K, P, Mn, Zn, Fe, Ni, Cu, Cr) in xylem. Five-year core segments were pooled with respect to distance from emission source, time of wood formation, and tree age (young trees <35 years; old trees >35 years). Soil analysis was done for all stands (total of 28) by soil layer (forest floor, A and B horizons) for pH, exchangeable K, Ca, Mg, Al, and oxalate-extractable Al and Fe. Also analyzed was the snowpack at each stand at three sampling dates in February and March 1986. The snow data for pH, Ca, Mg, K, and SO4 were highly variable, with some of the variability presumably related to fallout of fly ash. The soil data were also variable, but revealed a gain of water-soluble and bicarbonate-extractable SO4, and a loss of exchangeable Mg with increasing proximity to the power generator. Magnesium levels in the wood of the red spruce trees showed a similar trend. Wood concentrations for Ca, Mg, Mn, and Zn were found to decrease with increasing stand age. In contrast, wood concentrations for P, K, Fe, Ni, Cu, and Cr were highest in the most recently formed xylem. Some of these variations were probably affected (i) by the affinity of the wood for each element during wood formation, and (ii) by removal through flow of xylem sap. Some of these trends may also reflect changed ion availabilities in the soil or may be due to air pollution. Trends for the age-related variations of mean bole increments in each of the uneven-aged stands were probably affected by within-stand competition, modified by selective logging, and by recurring outbreaks of spruce budworm (Choristoneurafumiferana Clem.). An enhanced rate of SO2 emission since about 1965 may also have had a negative effect on radial bole growth. The availability of soil water appeared to be a principal factor in relating a tree growth index to year by year climate variations. This tree growth index (developed for an even-aged stand of red spruce upwind from the power generator) was positively related to precipitation of the preceding year and to precipitation in July and August (time of latewood formation). The growth index was negatively related to prolonged periods of high temperatures during earlywood formation.