Krasnoyarsk scientists have revealed that the lack of absorbed moisture in coniferous trees growing in permafrost conditions leads to disturbances in the structure of tree rings and wood cells. This causes the tops of the tree crowns to dry out. Since the 1980s, with the onset of intense warming and an increase in the aridity of the climate, changes in the structure of annual rings and wood cells have been detected, and this has significantly reduced their ability to transport water and dissolved substances from roots to crowns. The results of the study are published in the journal Contemporary Problems of Ecology.

In the north-taiga regions, coniferous trees with dry tops are often found. One of the possible reasons for their appearance is the water shortage that trees can experience in the specific conditions of permafrost.

Researchers of the Federal Research Center "KSC SB RAS" found that the shortage of water absorbed from the seasonally thawed soil layer affects the cellular structure of tree rings and the structure of the tree cells themselves, namely tracheids. This contributes to the top drying of the crown of coniferous trees. Scientists have also established a relationship between the tree ring growth at different stem heights and with different climatic factors.

The greatest effect of air temperature on the tree ring growth in healthy and damaged trees is observed during intensive growth, from late May to the twentieth of June. At the same time, the sensitivity to air temperature and the amount of precipitation in stag-headed trees is higher than in healthy ones. However, the main differences between the stag-headed and healthy trees are manifested in the structure of wood under the treetops rather than in the effect of different weather conditions on the growth rate of annual rings.

The scientists compared the tree ring width and the anatomical structure of the wood in healthy Gmelin larch trees and neighboring trees of the same species with dried crown tops that grow in the same stand in the Nizhnyaya Tunguska River basin. The tree rings in healthy trees at all levels of stem height turned out to be noticeably wider than in damaged trees. Since the 1980s, in other words, since the beginning of intense climate warming and with an increase in the aridity of the study area, the size of the cells in the upper part of tree stems under the dried top through which water and dissolved substances are transported from the roots to the crown has noticeably changed. The thickness of their walls has decreased by about a half as compared to healthy trees. The size of the cell gaps has also significantly decreased, reducing their ability to transport water and nutrients.

“Our data indicate a vivid response of trees to the effect of climatic factors. In general, damaged trees are more sensitive to weather conditions than healthy ones. The indicated features may be due to insufficient water supply to the upper parts of tree stems. This leads to a slow radial growth and low intensity of cell division in spring. As a result, relatively narrow tree rings are formed, consisting of a small number of cells with a reduced ability to transport water. This aggravates the lack of moisture entering the crown, and leads to the drying out of trees,” explained Dmitry Mashukov, junior researcher at the V.N. Sukachev Institute of Forest FRC KSC SB RAS.

The study was supported by projects of the Russian Foundation for Basic Research, the Russian Science Foundation, and a grant from the Government of the Russian Federation.