Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế, đề tài: "The effect of excess nitrogen and of insect defoliation on the frost hardiness of bark tissue of adult oaks. | Ann Sci For 1996 53 395-406 Elsevier INRA 395 Short note The effect of excess nitrogen and of insect defoliation on the frost hardiness of bark tissue of adult oaks FM Thomas R Blank Niedersachsische Forstliche Versuchsanstalt Abt B Gratzelstr 2 37079 Gottingen Germany Received 9 December 1994 accepted 31 October 1995 Summary Deep winter frost causing severe bark necroses and insect defoliation are two of the causal factors for the present oak damages in northern Germany. In earlier investigations a majority of oak stands had shown high leaf nitrogen concentrations. Therefore the effect of nitrogen status and of insect defoliation on the frost hardiness of the bark of adult oaks was tested. At several dates during winter samples from the living inner bark tissue were taken from adult sessile Quercus petraea Matt Liebl and pedunculate oaks Q roburL I with normal or elevated leaf nitrogen concentrations and ii defoliated or nondefoliated in the preceding spring. Frost hardiness of bark was determined by electrolyte leakage after artificial freezing in the laboratory. During frost periods in January and February oaks with lowered C N ratios in bark or leaves as well as defoliated trees tended to reduced frost hardiness. Although the differences were insignificant for some temperature treatments it is concluded that the effect of winter frost on oak damage is enhanced by a supply of excess nitrogen and by preceding insect defoliation. bark frost hardiness insect defoliation nitrogen oak decline Quercus Resume Influence d un excès d azote et de la defoliation par des insectes sur la resistance au gel du liber de chênes adultes. Les grands froids de I hiver qui produisent des necroses sévères du liber ainsi que la defoliation causée par les insectes sont deux causes probables du dépérissement actuel des chênes en Allemagne du Nord. Dans la majorite des peuplements de chêne explores on a détecté une forte concentration d azote dans les feuilles. On a done recherche I .
