Special Feature: Recent problems in oak decline Preface

Abstract

Occurrence of severe dieback, decline, and mortality in oak (Quercus spp.) stands have been reported frequently during the last 20 years in various parts of the world. As a result, numerous research activities have been initiated. 'Recent Problems in Oak Decline' was also the topic of a meeting of the International Union of Forestry Research Organizations (IUFRO) units Sl.06.00, S2.06.00 and S2.07.00 at the IUFRO XX World Congress held in Tampere, Finland during August 1995. A selection of five papers presented during this meeting is published in this issue in which symptoms of oak damage are characterized and potential causal factors as well as factor combinations (insects and fungi, climatic factors, site-related aspects, genetics) are described. DONAUBAUER, Austria, summarizes the macroscopic symptoms of oak decline and reports on the regional role of parasites as predisposing and as contributing factors. S!WECKI and UFNALSKI, Poland, give a review of oak stand decline in Poland with special reference to the role of climatic factors. They found that climatic conditions had a decisive influence on the vigour of Quercus robur. Increased frequency of dry years resulted in the complex phenomenon of oak decline. STEINER, USA, observes oak decline in the context of genetic management. In order to minimi ze susceptibility to oak decline he suggests forest practices which favour the maintenance of high levels of genetic variation and the use of local provenances in artificial regeneration and large seedling populations. Prediction models for estimating mortality of oak due to gypsy moth (Lymantria dispar), based on a new analysis using defoliation intensity classes as a variable along with species, crown position, and crown condition, are presented by GOTTSCHALK et al. USA. STANDOVAR and SOMOGYI, Hungary, stress the importance of site characteristics and tree growth. Oaks seem more susceptible to decline outside of their natural range. Most presentations stressed the necessity for further investigations because the results are still preliminary and there is a wide variation in responses . The various methodological approaches used in these papers are of special interest. We hope that this collection of papers contributes to the progress on the long path to a better understanding of oak ecosystems and of improving the health of the world's oak forests.