Abstract
Forest health is currently assessed in Europe (ICP Forests monitoring program). Crown defoliation and dieback, tree mortality, and pathogenic damage are the main aspects considered in tree health assessment. The worsening of environmental conditions (i.e., increase of temperature and drought events) may cause large-spatial scale tree mortality and forest decline. However, the role of stand features, including tree species assemblage and diversity as factors that modify environmental impacts, is poorly considered. The present contribution reanalyses the historical dataset of crown conditions in Italian forests from 1997 to 2014 to identify ecological and structural factors that influence tree crown defoliation, highlighting in a special manner the role of tree diversity. The effects of tree diversity were explored using the entire data set through multivariate cluster analyses and on individual trees, analysing the influence of the neighbouring tree diversity and identity at the local (neighbour) level. Preliminary results suggest that each tree species shows a specific behaviour in relation to crown defoliation, and the distribution of crown defoliation across Italian forests reflects the distribution of the main forest types and their ecological equilibrium with the environment. The potentiality and the problems connected to the possible extension of this analysis at a more general level (European and North American) were discussed.
Highlights
Health conditions of European forests are assessed since some decades in an extensive network (Level I) within the ICP Forests program (International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests)
Among broad-leaves, Fagus sylvatica L. is distributed at the intermediate elevation (800–1200 m a.s.l.) in the Alps, and it is the most common species at the high elevation (1000–1500 m a.s.l.) in the entire Apennine chain in Central and Southern Italy
While broadleaved tree species are widespread over the whole Italian territory and across different climatic regions, conifers are represented mostly by alpine species (P. abies, Larix decidua Mill., P. sylvestris) each of them occupying a specific ecological niche with a distribution limited to Northern Italy (Fig. 1a)
Summary
Health conditions of European forests are assessed since some decades in an extensive network (Level I) within the ICP Forests program (International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests) This program was launched as part of CLRTAP (Convention on Long-Range Transboundary Air Pollution) implemented by EMEP (European Monitoring and Evaluation Programme) and directed by UNECE (United Nations Economic Commission for Europe) and was primarily devoted at assessing the effects of atmospheric deposition and air pollution on forests. Focused on air pollution, new environmental challenges such as climate change and pathogenic invasions are included in recent years within the goals of the program (ICP Forests 2016). In this new perspective, the suitability of the tree health indicators. Climatic fluctuation and extremes have been recognized as the main powerful factors that drive spatial distribution and temporal changes of forest tree health, vitality, and productivity (Carnicer et al 2011; Ferretti et al 2014; de la Cruz et al 2014; Bussotti et al 2015; Popa et al 2017)
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