SIMILAR PATTERNS OF CHANGE IN STEMWOOD CALCIUM-CONCENTRATION IN RED SPRUCE AND SIBERIAN FIR

Changes in stemwood calcium concentration ([Ca]) for the last 120 year s occurred in a common pattern for two sample collections of red spruc e (n=33 and 20) from the northeastern United States and for one sample collection of Siberian fir (n=20) from southcentral Siberia, Russia. The [Ca] was measured for wood formed during the periods 1871-90, 1891 -1910, 1911-30, 1931-50, 1951-70 and 1971-90. For each core, the relat ive increase or decrease in [Ca] for adjacent periods of wood formatio n was recorded. The relative frequency of positive change in [Ca] for each period of wood formation was calculated for the three sample coll ections. Previous research indicated that under equilibrium conditions , [Ca] in stemwood tended to decrease in more recently formed wood, du e to declining numbers of Ca binding sites. Consequently, we expected a low frequency of positive changes in [Ca] in successively formed woo d. Consistent with expectation, the relative frequency of positive cha nge from the preceding period to the periods 1891-1910, 1911-30, 1931- 50, and 1971-90 were low. Contrary to expectation, the frequency of po sitive increases in [Ca] more than doubled in 1951-70 compared to 1931 -50. The frequency of positive increases in the 1951-70 period relativ e to the preceding period was 48%, significantly greater than all othe r periods (P less than or equal to 0.01). The frequencies of positive increases for all other periods were not significantly different from each other (overall mean = 21%, SD = 7). This anomaly in the frequency of positive change in [Ca] in wood formed in 1951-70 relative to wood formed in 1931-50 indicated a perturbation in the ion exchange chemis try of stemwood in two widely separated parts of the northern conifero us forest. This anomaly could be due to external or internal factors. Changes in sap chemistry that affected stemwood chemistry could have b een due to changes in the rooting zone. Such changes in rooting zone c hemistry could result from the atmospheric deposition of ionic polluta nts. Other external factors that could cause the observed anomaly incl ude unusual climatic periods or environmental disturbances such as log ging or fire. Internal factors that might produce an anomalously high frequency of positive change of [Ca] include heartwood formation, stem wood infection and a hypersensitive response of the tree against infec tion.