Forest growth and climate change: evidences from the ICP-Forests intensive monitoring in Italy

A few concurrent and/or counteracting factors (increase of average air temperature, rainfall shortage, drought, CO2 enrichment, ozone, nitrogen fertilization, sulphate deposition) drive today the soil-tree-atmosphere relationships in the Mediterranean area. Radial stem growth measured within the ICP-Forests level II Italian network provides a sensitive response to these occurrences. Climate fluctuations and repeated anomalous seasons or extreme events are the major evidences of the change in progress. The 2003 heat wave is the main event occurred in this decade over large part of Europe. In Italy, it provoked a marked water deficit coupled to high air temperature, which resulted in a heavy water stress. The growth performance in different forest types was analyzed in this paper: growth rate in 2000-2004, compared with 19971999, showed reductions up to 50% on half of the plots examined. Most of them were: (i) in northern-central Italy within the southern continental border of the climatic deviation; (ii) at low elevation, which is more sensitive to high air temperature and drought; (iii) made up of deciduous broadleaved forests (beech and oaks), i. e., species showing growth effects also in the following year. Over the time-window 2005-2009, a significant growth decrease was vice-versa detected within the coniferous spruce forests located at medium-high elevation in the Alps. Repeated seasonal deviations in temperature and rainfall were recorded in the Alps in 2005-2009. Climate effects at local scale were examined in a site where two oak species with a different auto-ecology (sessile oak and Turkey oak) grow together. The on-going change produced heavy mortality and reduced the growth of the more demanding and less drought-tolerant sessile oak; in a few years Turkey oak became prevailing in the stand composition and structure.