Deviations of treeline Norway spruce radial growth from summer temperatures in East-Central Europe

While some cold regions show evidence of recent decoupling of tree-ring growth from observed temperature rise, i.e. restricted growth increase, similar evidence from other regions is missing. Increasing or diminishing regional coherency in tree growth has also been observed over recent decades. The temporal and spatial extent of the abovementioned processes are poorly known and their drivers are not well understood. Pollution and changing climate have often been discussed as a cause of divergent or convergent growth patterns and deviations of growth from driving climatic variable. We compiled climatic records and robust tree-ring chronologies of treeline Picea abies covering 1920-2010 for four regions in East-Central Europe (Czech Republic, Poland, Slovakia, 50 degrees N, 15-20 degrees E) which experienced differing acid pollution loads. The divergence of these chronologies from Jun-Jul temperatures was compared with temperature and pollution trends. We found a period of low intra-regional growth coherency in the 1950s reflecting warmer, less temperature-limiting conditions and land use change. Highly coherent growth in the 1930s, 1970s and 1980s was related to the strong environmental growth limiting signals of short growing seasons and high acid pollution loads. In all regions, we identified periods with higher (1940-1960s) and lower (1970-1980s) growth than expected based on temperature. In the high-frequency domain, the effect of pollution on growth departure from temperature was limited and detectable exclusively in regions that were most impacted by pollution. In the low-frequency domain, the departures of growth from temperature were caused by combined effects of the changing seasonal window of tree growth sensitivity to climate and pollution load. These results highlight the need to recognize non-stationary noise in the relationship between temperature and tree growth.