Tree health and annual and periodical radial growth in coniferous trees in northern Italy

With the 2018 megadrought causing widespread canopy damage to forests in central Europe, the question whether this can result in reduced tree and forest growth became of renewed interest. Such a question has clear relevance for the functional interpretation of forest health data as collected in Europe since the 1980s and in the climate change debate. For instance, Rohner et al. (2021) showed that droughtinduced defoliation and leaf browning are associated with lower growth- and carbon sequestration rates. Here we investigated relationships between tree health indicators (crown defoliation, damage) on annual (measured by tree-ring width on 69 Norway spruce trees) and periodical (expressed in terms of 5-10 years Basal Area Increment for 346 trees from five coniferous species) tree growth. Data originated from seven ICP Forests Level I plots and one Level II plot in Trentino, northern Italy. Diameter, defoliation and damage data were collected between 1997 and 2011 as part of the annual crown condition survey carried out by the local forest service. Two cores per tree were collected from haphazardly selected dominant trees at each monitoring plot in 2012. Our first results involving within tree means of log ring width and square root defoliation indicated a slight negative correlation (-0.26). We also fitted simple linear models to single tree data and obtained plot level estimates of slope parameters. Bootstrap analysis of these estimates also confirmed a significant negative association between defoliation and ring width. We will further investigate possible generalized relationships between tree health and growth in various time windows (annual, 5 or 10 years), across different species, site factors and defoliation level.