Interactive effect of extreme climatic event and pollution load on growth and wood anatomy of spruce

Key message Air pollution intensified the effect of climatic extreme and left a detectable mark in growth and wood-anatomy parameters over 3–5 years following the stress event. The forests in the region of so-called “Black Triangle” suffered from heavy air-pollution load until the end of the 1980s. Acid deposition reduction in 1990s led to an improvement of forest condition. However, the positive development was interrupted by an extreme climatic and pollution stress during the winter of 1995/96. It resulted in an acute damage of spruce stands, manifested by drying and falling of needles and significant decrease of bud vitality. The methods of tree-ring and quantitative wood-anatomy analysis were employed to study the impact of this event on growth and wood anatomy of Norway spruce ( Picea abies (L.) Karst.). Reexamining the tree response remains challenging, because the knowledge about the impact of acute pollution stress on xylem traits is still lacking. The annual radial growth showed a clear reaction to the stress event, manifesting as a strong growth reduction in 1996–1998. Height growth was affected in similar manner, but only recovered in 2001. Anatomical features of both earlywood (EW) and latewood (LW) were affected by the stress, however, with the maximal effect occurring with a lag of 1 year from the time of the event. The EW part was more responsive and showed a higher variability of parameters than the LW part. During the 1996–2000 stress period, tree growth was driven by climatic factors and by the air-pollution load; later, the impact of air pollution was no longer pronounced and tree growth was correlated to the content of nutrients.