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Oak decline in a southern Finnish forest as affected by a drought sequence

Sohar K., Helama S., Läänelaid A., Raisio J., Tuomenvirta H.

Geochronometria

2014

Vol. 41, no. 1

92--103

We investigated the decline of a pedunculate oak (Quercus robur L.) forest growing on shallow soil at the northern distributional limit of the species in southern Finland, using the dendro-climatic approach. About 200-year-old trees in three vigour classes – healthy, declining and dead – were sampled in 2008. Annual tree-ring, earlywood and latewood widths were measured and chro-nologies were established. The tree-ring data were correlated with monthly and seasonal climate data. Radial increment of oaks was positively related to the June and July precipitations. This was ex-pressed especially in total ring width and latewood width, whereas the earlywood was more influ-enced by the warmer winter and spring. Furthermore, the correlation between the current year ear-lywood width and the preceding year latewood width was higher than between the earlywood and latewood of the same year. The analyses showed that the dead oaks and part of the declining oaks had ceased growing during 2005-2007 after a decade-long summer drought series. This indicates a time lag in the oak dieback. The radial growth of the declining and the dead oaks had dropped already since the 1990s, while the healthy oaks had better long-term growth and higher adaptive capacity to climate variation.

A dendrochronological analysis of Pinus pinea l. on the Italian mid-Tyrrhenian coast

Piraino S., Camiz S., Filippo di A., Piovesan G., Spada F.

Geochronometria

2013

Vol. 40, no. 1

77-89

In order to assess the response of the radial growth of Pinus pinea L. to climatic variability in Central Italy, dendrochronological and dendroclimatological analyses were carried out on five different populations scattered along the Tyrrhenian coasts of the peninsula. The aim of this study is to contribute to the understanding of the ecological demands of this species, particularly in the study area. For each site total ring, early-, and late-wood width chronologies were developed. Multidimensional analyses were performed for the three tree-ring datasets in order to analyze the rela-tions between sites chronologies. Both Principal Component Analyses and hierarchical classifications highlighted an important difference of one site in respect to the other, probably due to site characteris-tics. Correlation functions were performed to infer the main climatic factors controlling the radial growth of the species. For a comparative study, we limited our attention to the common interval 1926-2003 (78 years) in which the response of the tree-ring chronologies to climate at both local and regional scale was investigated. Positive moisture balance in the late spring-summer period of the year of growth is the climatic driver of P. pinea radial growth in the study area. Moreover, this study shows how low summer tempera-tures strongly favor the radial growth of the species.