Some aspects of alder decline along the Lužnice River

Abstract

Alder decline along watercourses is one of the marked manifestations of tree decline in the Czech Republic. Local decline of alder trees is documented in the Czech Republic for about 15 years. The aim of this paper is to evaluate causes of alder decline and assess health conditions of other species of riparian stands at 2 localities on the medium reach of the Lužnice River. Effects were studied of abiotic and biotic stressors on the health condition of tree species. No fungal pathogen was found in tissues of declining alders which would be present in all trees and which could be considered to be the main causal agent of the decline. Even an occurrence of the causal agent of alder decline named alder-Phytophthora has not been proved. Tree-ring analyses demonstrated decreasing trends of an increment in alders; however, an abiotic or biotic factor showing direct effects on the fluctuation of tree ring dimensions has not been positively determined. A marked role in the alder decline is demonstrated particularly by abiotic factors accompanied by the secondary activation of some pathogens. Generally, the phenomenon can be named as polyetiologic decline.

Keywords

• alnus
• decline
• tree-ring study
• fungi
• pathogens
• environmental stress