Spatial distribution of introduced Norway spruce growth in lowland Poland: The influence of changing climate and extreme weather events Marcin Koprowski Nicolaus Copernicus University, Institute of Ecology and Environment Protection, Laboratory of Dendrochronology, Gagarina 9, 87-100 Torun, Poland article info Article history: Available online 20 April 2012 abstract Norway spruce trees grown outside their natural range were intensively studied in terms of their adaptability to increased late winter temperature. A total of 708 cores of Norway spruce were taken from 35 sites throughout northwestern and western Poland at sites outside or at the margin of its natural range. Clustering reveals that research sites are grouped geographically. The mean ring widths, however, are similar among the three regions. The relationships between tree growth and temperature together with precipitation are comparable to those in lower elevations in Central and Eastern Europe and southern latitudes in Scandinavia. In total, 18% of the single correlations for all months were significant at p < 0.05. The generally positive precipitation effect was found for all months except January. Temper- ature had mixed effects on ring width. Higher temperatures in late winter and early spring increased ring width (13% of all significant correlations). High summer temperatures in both the previous and the current year, on the other hand, generally had a negative impact on tree-ring width during the growing season. On most of the sites, the observed long-term trend for increasing temperatures in February and March had no significant negative influence on tree growth. Also the effect of extreme weather events was taken into account. In 1994 and 1995 the wider rings were mostly observed in humid sites from southwestern Poland. In selected time spans, growth recovery following extreme weather events is particularly strong. Ó 2012 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Norway spruce (Picea abies [L.] Karst.) occurs naturally in the northeastern and southern parts of Poland while its natural occurrence in the central part of eastern Poland remains contro- versial (Fig. 1)(Lata1owa and van der Knaap, 2006; Dering and Lewandowski, 2009). During the last 200 years spruce has been planted, particularly in mountain areas of southwestern Poland and in the lake-lands of northwestern region. As a result, the occurrence of spruce has been extended to large areas outside its natural range (Boraty nski, 1998) and the importance of this tree in forest management has increased. In the case of spruce, the major influences on geographical distribution other than climate are the evolutionary-genetic tree tolerance, extreme weather events (Podbielkowski, 1991), and negative impact of management activity together with unfavourable soil conditions (  Srodo n, 1967). The effects of climatic change have been observed in Poland (Ko _ zuchowski and Degirmend zi c, 2005), and its impact on tree growth may differ within selected time spans. Further, tree-ring increment patterns might differ across larger regions due to meso-scale differences in climate. In the last 50 years Central Europe has seen increasing average temperatures and higher minimum temperatures in February and March, and thus an earlier onset of spring by more than two weeks (Ko _ zuchowski and Degirmend zi c, 2005). The impact of these higher temperatures on the growth and health status of Norway spruce is still not fully understood. Because spruce is the second most important tree species after pine in Polish forests (Boraty nski and Buga1a, 1998), improved understanding is clearly needed on the impact of climate change on the ecology and growth of spruce (Koprowski and Zielski, 2006). The present work therefore has three major aims: 1. To identify the climate parameters that affect the growth of Norway spruce outside its natural range and to compare these patterns to those found for spruce within its natural range. The latter is already sufficiently known for many European natural stands (Mäkinen et al., 2003; Andreassen et al., 2006; Koprowski and Vitas, 2010). The study of trees outside the natural range might help to determine how spruce reacts after E-mail address: koper@umk.pl. Contents lists available at SciVerse ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2012 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2012.04.020 Quaternary International 283 (2013) 139e146