Abstract

During the last decades of the 20th century, the condition of oak species throughout Europe generally deteriorated. In southern Sweden, oak decline represents a recent phenomenon with complex temporal and spatial patterns. In this region, crown defoliation of the most common oak species, pedunculate oak Quercus robur, increased by >20% from 1988 to 1999. In 1999, 59% of the oaks were considered damaged, i.e. showing >25% crown defoliation. However, a trend of improving crown conditions was observed in southeastern Sweden during 2000-2008. Available research suggests unfavorable climatic variability as the main cause of negative dynamics in oak crown conditions. Studies have demonstrated the important role of climatic extremes (e.g. cold winters during the dormant season and drought events during vegetation season) in initiating decline phenomena, and a strong correlation between crown condition dynamics and tree-ring increments. Phytophthora quercina (class Oomycetes, kingdom Chromalveolata), a soil-born pathogen of oak, is present in declining oak stands with soil pH (BaCl2) >3.5. The role of Phytophthora spp. in initiating the decline in southern Sweden remains unclear, since most oaks stands in this region have more acidic soil conditions (pH < 3.5). Similar to other European studies, our results point to the multi-factorial nature of oak decline and the importance of stand conditions in decline dynamics. This paper reviews recently published studies on the topic and presents a simple conceptual model of oak decline. We discuss future research themes that may advance our understanding of oak decline

Published in

Ecological Bulletins
2010, volume: 53, number: 53, pages: 197-207
Book title: Broadleaved Forests in Southern Sweden: Management for Multiple Goals
ISBN: 978-1-4051-8886-9
Publisher: The Nordic Society Oikos

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