Effects of spatial and temporal variability in soil moisture on widths and δ¹³C values of eastern Siberian tree rings

Abstract

We studied the relationships between earlywood/latewood width, stable carbon isotope ratio (δ 13 C) of cellulose, and soil moisture at a dry and a wet site in Yakutsk, eastern Siberia, which differed considerably in soil water conditions. Recharge of soil water by snowmelt in spring and subsequent drought in summer provided a marked seasonal contrast in soil water conditions between the earlywood and latewood formation period. Ring index was calculated by dividing each earlywood/latewood width by the 5‐year averaged width for each individual. In order to determine whether drought influenced the ring index‐δ 13 C relation, the ring index time series were compared with δ 13 C time series. We collected wood samples from eight Larix gmelinii (Rupr.) Rupr. and four Pinus sylvestris L. trees from the two sites and measured the earlywood and latewood widths and δ 13 C of earlywood and latewood formed during the years 1996–2000. At the dry site, seasonal soil water content variation corresponded to seasonal δ 13 C variation of tree rings. We found negative ring index‐δ 13 C correlations in latewood for both species at the dry site mainly dominated by Pinus but not in latewood of Larix at the wet site dominated by Larix . Decrease and/or early cessation of latewood growth and increase in δ 13 C under drought conditions possibly explain this negative correlation. This suggests the growth limitation of trees in this region by drought and the prospects of reconstructing past drought with latewood δ 13 C of the dry site.