Dendrochemical Challenge in Climate Science: Whether Chemical Elements in Wood Reflect the Fluctuations in Weather Parameters.

The aim of this study was to find consistent correlations between weather parameters and elemental content of tree rings in four widely distributed Siberian conifers: Siberian spruce (Picea obovata Ledeb.), Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and Siberian pine (Pinus sibirica Du Tour). Slices from the wood cores were subjected to chemical treatment by extraction in alcohol and HCl. The slices were scanned using an Itrax Multiscanner (COX Analytical Systems) to obtain the count rates of Al, P, S, K, Ca, Ti, Mn, Fe, Cu, Zn, and Sr. Every slice was scanned three times, in the original form, after alcohol extraction, and after HCl treatment. Altogether, 21 weather parameters were used to search for consistent correlations between the elemental contents. Weather parameters as well as elemental contents were averaged for successive triplets of calendar years. The statistical treatment of the data included the calculations of non-parametrical Spearman rho and Kendall tau coefficients. We defined consistent correlation as a correlation that is stronger than +/-0.3, observed in all the trees studied, and is significant at least in one tree. The main result of the study is that no consistent correlation was found that we could observe in all the species involved in the study. Nevertheless, there are several consistent correlations within the species. This means that the right choice of species for a dendrochemical study is of paramount importance. In some species, e.g., the larch and spruce, we found no correlations unless the chemical treatment was applied. Thus, a chemical treatment may reveal the reactions of tree rings' elemental content to some weather parameters.

Two-Species Forests at the Treeline of Siberian Mountains: An Ecophysiological Perspective under Climate Change.

In an underexplored region of the East Sayan mountains, ecophysiological traits of two conifers, Pinus sibirica Du Tour and Abies sibírica Ledeb., have been studied. The goal was to predict which of the species co-dominating the same habitat is more vulnerable under prospective climate change. Along a transect from the treeline to the floodplain, photosynthetic pigment content and electron-transport rate (ETR) were measured in needles of neighboring trees of the species. From 570 to 1240 m a.s.l., P. sibirica does not suffer from stress factors during the growing season, while A. sibirica does. The latter is reflected in a decrease of pigment content and ETR with the increase of altitude. A stronger climate-change trend (probably to more dry and warm conditions) will likely favor the shift of P. sibirica upper in altitudes, and only under the pine shelter might the fir survive the changes.

Turnover of 137Cs in 'soil-tree' system: An experience of measuring the isotope flows in a Siberian conifer forest.

Little attention has been paid to the uptake of 137Cs in natural forests under low levels of the isotope fallout when no immediate ecological danger presents. Here we present the extended assessments of the soil-to-plant and canopy-to-litter flows of 137Cs recently evaluated in a native Siberian forested area. The area undergoes a typical after-fire long term succession, with light-conifer upper story being followed by undergrowth of Siberian fir and other dark-conifer species. The one-year-old needles of Siberian fir were found to accumulate the largest concentration of the isotope, 4.10 Bq/kg oven-dry weight during the first growth season, as compared with older needles that accumulated 4.67 Bq/kg oven-dry weight in 2-3 years of growth. Based on these data an approach was developed that, hypothetically, can allow one to estimate the 137Cs activity concentration in soil solutions. Direct activity measurements in the soil solutions were not possible. The isotope activity in soil solutions was estimated to be 0.0061-0.0105 Bq/L. Based on the original data from the litter fall the annual flow of the isotope from the upper canopy to on-ground litter was found to be 0.42-0.84 Bq/m2. The amount of 137Cs that returns yearly back from canopy with falling litter was estimated to be 0.012-0.015% of the total soil isotope content. A combination of the estimations obtained in our study with the values of global 137Cs fallout allowed us to assess the ages (the time of formation) of horizons of the soils in the area.