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DECLINE HISTORY OF OAKS IN 20TH CENTURY FOR ROMANIAN EXTRA-CARPATHIAN REGIONS

Constantin Nechita

Abstract

Oak stands decline has been several times reported in the scientific literature, starting with the beginning of the twenty century. A brief overview is presented regarding the occurrence of oak decline in the Romanian extra-Carpathian region since 1900 until present. Six oak species having a significant economic and ecological status are affected - Quercus robur L., Quercus petraea (Matt.) Liebl.), Quercus pedunculiflora K. Koch., Quercus frainetto Ten., Quercus cerris L., and Quercus pubescens Willd. The literature mentions a first widespread phenomenon in 1914, followed by another one in 1932. Based on the historical records, these phenomena were assigned to the climate changes effects (summer drought), defoliating insects or pathogenic fungi. The occurrence of oak decline in the next rainy years, in different ecosystem conditions, promoted other hypotheses such as vegetative origin, past management or anthropogenic influence. The present dendrochronological research shows the effects of air pollution, chemical stress of soil, climate extreme, and complex site condition. In the present, usually the biotic stress induced by insect defoliation, infection with pathogenic fungi and bacteria represents the first indicators of decline. We present a detailed review on the oak woods decline with the analysation of the hypotheses explaining this phenomenon.

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