The Sudetes form a medium size mountain barrier straddling the border between Poland and the Czech Republic. They are covered predominantly by spruce forest, in the western part of the massif reborn after the ecological disaster of the 1980s. The aim of this study is to explain the dynamics of annual tree rings of spruce in the context of present climatic condition. Over the past two decades, the Sudetes have recorded a clear upward trend in temperature and increasingly frequent droughts. Between 2018 and 2023 the increase of mean air temperature was 1.2 ºC and the annual precipitation decreased by 15%.
To examine the response of trees to factors influencing their growth, around 1070 core samples from 52 locations were collected between SEP 2022 and NOV 2023. On the basis of elaborated tree ring series, two periods were selected to show the dynamics of spruce forest health: (A) recovery period 2001-2010 and (B) present negative trend 2018-2023.
The values of tree ring dynamic in period “A” were positive at slopes position, flat valley-basis and ridges (+13%, +26% and +26% respectively) whereas at the foothills it was slightly negative (-9%). In period B the tree rings were reduced at all landform categories with highest reduction -29% at both foothills and southern slopes. In the case of individual locations, the reduction was even greater than -40%.
The first decade of the 21st century (period A) shows a strong positive reaction of spruce trees at medium and high altitudes which can be explained by much smaller acid deposition combined with better light conditions for the remaining trees after previous dieback. At the foothills, where climate is relatively mild, the reaction remained slightly negative, because of climate change effects gradually deteriorating conditions suitable for the spruce. In period B, climate change negatively influenced spruce growth at all landforms, particularly the warmest landform category where southern aspect enhances the role of solar radiation.
Optimal conditions for spruce growth occurred before the recent acceleration of global warming in relatively wet 2001-2010 period. Nowadays worse conditions are visible, especially where temperatures are too high and seasonal water shortages become frequent.