Temporal shifts of climate-growth relationships of Norway spruce as an indicator of health decline in the Beskids, Slovakia

Norway spruce (Picea abies) is one of the most widespread and economically valuable tree species in Europe, however recently it has been experiencing a large-scale decline. In the western Carpathians, particularly forests in the Beskids Mountains have recorded the most extensive health decline ever documented. Climate change during the last several decades has had a significant impact on the functioning of these forest ecosystems. To contribute to the debate on the causes of the spruce decline we conducted a dendroecological study in the Beskids Mountains. A large sample of ring-width series were collected along a transect spanning the large range of ecological conditions in the region. Non-metric multidimensional scaling was used to identify structural similarities between spruce trees in terms of their response to climate variation and to identify the most relevant site- and stand-related variables. Cluster analysis was applied to identify relevant groups of trees. Step-wise linear regression was used to build climate-growth models for chronologies in the clusters. A shifting correlation in 20-year moving segments was used to identify temporal change in spruce climate-growth relationships. Results show that needle loss significantly changed the character of the response when trees with different intensity of defoliation, growing at the same altitude, responded oppositely to the mean summer temperature. In addition, we observe shifts in the climate-growth relationships of spruce trees to spring and summer temperatures when the relationship of trees without or with low defoliation started to decline between 1990 and 1998. This deterioration indicates three hypotheses: (i) climate change; (ii) trees that were considered healthy when observed might have started to decline, and this will be visually detectable in the near future; and (iii) rapid reduction of emissions in interaction with the recent climate change. (C) 2014 Elsevier B.V. All rights reserved.