Publication Date:
2012-10-10
Description:
Growth-climate relationships were investigated in Greek firs from Ainos Mountain on the island of Cephalonia in western Greece, using dendrochronology. The goal was to test whether tree growth is sensitive to moisture stress, whether such sensitivity has been stable through time, and whether any changes in growth-moisture relationships support an influence of atmospheric CO 2 on growth. Regressions of tree-ring indices (AD 1820–2007) with instrumental temperature, precipitation and Palmer Drought Severity Index (PDSI) indicate that growth is fundamentally limited by growing-season moisture in late spring/early summer, most critically during June. However this simple picture obscures a pattern of sharply evolving growth-climate relationships during the 20 th century. Correlations between growth and June temperature, precipitation, and PDSI were significantly greater in the early 20 th century but later degraded and disappeared. By the late 20 th –early 21 st century there remains no statistically significant relationship between moisture and growth implying markedly enhanced resistance to drought. Moreover growth experienced a net increase over the last half-century culminating with a sharp spike in AD 1988–1990. This recent growth acceleration is evident in the raw ring-width data prior to standardization, ruling out artifacts from statistical detrending. The vanishing relationship with moisture and parallel enhancement of growth are all the more notable because they occurred against a climatic backdrop of increasing aridity. The results are most consistent with a significant CO 2 fertilization effect operating through restricted stomatal conductance and improved water use efficiency. If this interpretation is correct, atmospheric CO 2 is now overcompensating for growth declines anticipated from drier climate, suggesting its effect is unusually strong and likely to be detectable in other up-to-date tree-ring chronologies from the Mediterranean. © 2012 Blackwell Publishing Ltd
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
,
Energy, Environment Protection, Nuclear Power Engineering
,
Geography
