Low pre-death growth rates of oak (Quercus robur L.)—Is oak death a long-term process induced by dry years?

Background and purpose A complex interplay between biotic and abiotic factors is believed to be responsible for several oak declines in pedunculate oak (Quercus robur L.). This study aims to clarify the temporal process of oak declines, as well as identifying individual tree and environmental variables that affects growth rate and that may increase the risk of mortality. The study was performed in southern Sweden at three sites. Findings Cross-dating revealed that most trees had died during the last decade and that the growth rates of the dead oaks were affected long before death. Averaged growth chronologies of dead and control trees reaching 150 years back in time illustrated an excellent match up until around 1992, when a severe drought occurred after which the dead trees started to express reduced growth. Precipitation the previous year during August-September and during March-June this current year was of significant importance for oak growth. Site-specific results that showed that dead trees: included fewer small-sized trees, grew on non-clay soils, were more likely to have shelf fungus and cavities and were exposed to less sunshine. Conclusion The results support the theories that oak mortality is a long process that may be induced decades before the actual death.</p

Influence of repeated defoliations by insects on wood increment in common oak (Quercus robur L)

International audienc

Influence of repeated defoliations by insects on wood increment in common oak (Quercus robur L)

The dynamics of radial wood increments were analysed over a 30 year period in oak stands (Quercus robur) of the forest-steppe zone in the Voronezh region (eastern-central Russia). Relative losses in wood increment, due to insect-caused defoliations of diverse extents and periodicity, were quantitatively assessed. Such estimates were made for trees with early and late phenology, as well as with respect to growth classes and to local forest types. The intensity of the responses of dominant and codominant trees were shown to vary in different forest types. No differences in increment losses were detected between early and late oaks after one to three moderate defoliations. A factor two variation was observed in the intensity of the responses, depending on actual climate. In response to repeated defoliations, the ratio latewood to earlywood was reduced by a factor 5-8 in a stand and even 20 in an individual tree. This suggests that insect defoliation severely affects oak growth.Effets de défoliateurs sur la croissance de chênes (Quercus robur L). Les dynamiques de croissance radiale ont été suivies sur une période de 30 ans sur des chênes pédonculés (Quercus robur L) de la steppe forestière de la région de Voronezh (Russie centre-orientale). Les pertes relatives de croissance radiale dues à des défoliations par des insectes ont été évaluées quantitativement. Ces estimations ont concerné à la fois des chênes tardifs et précoces, ainsi que différentes classes de dominance, et divers types forestiers. L'intensité des réponses d'arbres dominants et codominants variait en fonction de la station. En revanche, aucune différence de sensibilité n'a été détectée entre variétés précoces et tardives en réponses à des séries d'une à trois défoliations modérées. L'intensité des réponses variait d'un facteur 2 en fonction des conditions microclimatiques. En réponse à des défoliations répétées, le rapport bois de printemps bois d'été était diminué d'un facteur 5-8 dans un des peuplements, et même de 20 sur un arbre isolé