Beech decline on periodically wet soils associated with Phytophthora root-rot
1998
Hartmann, G.
Causal factors of decline and mortality in 88-154 years old beech stands were investigated in 5 stands, situated in the colline parts (Weser-Leine-Bergland) of southern Lower Saxony. Symptoms are crown thinning, small yellowish leaves, dieback, root and collar-rot and bleeding cankers at the base of the stems. From advancing edges of cankers and from roots of declining trees with surrounding soil, Phytophthora cambivora (Petri) Buism. and P. syringae (Klebahn) were isolated, mainly during the dormant season and in spring. Isolation was also successful from roots with adhering soil of recently windthrown beech trees, which had not shown any serious symptoms before. The most frequent isolate resembles P. cambivora (Petri) Buism. Secondary fungi, mainly Nectria sp., and insects (Agrilus viridis, Taphrorhychus bicolor) contributed to the decline. Mortality was restricted to lower slopes and depressions. There the loamy water retentive soils (Cambisol and Luvisol) are characterized by a shallow well drained upper layer and impeded drainage in the subsoil. Very high precipitations in winter 1993/94 and in spring 1994 have cause water-logging in lower slopes and depressions and triggered Phytophthora root-rot. Subsequently very high temperatures and drought during summer 1994, which repeated in summer 1995, have aggravated the decline. It was shown by tree ring analysis that the present decline has started in 1994-1995 and that similar weather conditions had triggered an earlier decline during 1981-1983. Some seriously damaged trees survived this event in poor condition until today. This suggests that decline may repeat more often and the after-effects may drag until the next triggering event. Thus beech stands on predisposing sites may be permanently destabilized.
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