Relationships between health of Quercus robur, occurrence of Phytophthora species and site conditions in southern Sweden

Abstract

The effect of Phytophthora species, soil chemistry, precipitation and temperature on the vitality of oak was evaluated in 32 oak stands in southern Sweden. In addition, the relationship between the occurrence of Phytophthora species and soil conditions was determined. The results showed that there was a weak association between the presence of P. quercina , the most frequently recovered Phytophthora species in southern Sweden, and the vitality of the oak stands (determined from estimates of crown defoliation of individual trees). The pathogens occurred more frequently in clayey and loamy soils that were less acidic and which had higher base saturation. However, they were found in all but the most acidic soils (pH < 3·5). In stands where Phytophthora species were not present, positive correlations between the average crown defoliation and proportion of damaged trees with average summer precipitation and average annual precipitation were found. There were no significant differences in soil chemistry between healthy and declining stands included in this study, and no significant correlations were found between any soil parameter and crown vitality. Based on the results from these 32 oak stands, it is likely that the decline of oaks in southern Sweden can be attributed to several different site-specific factors, such as infection by P. quercina or unusual weather events, which interact with a number of biotic and abiotic factors, leading to oak decline.

CanPhytophthora quercinahave a negative impact on mature pedunculate oaks under field conditions?

“…In noninfested stands, on the other hand, no significant differences in live fine-root length could be detected between trees of different vitality. The completely different patterns of root growth in infested compared with non-infested stands, together with the symptoms of pathogen infection on roots of trees in infested stands, indicate a significant negative impact of P. quercina on fine-root systems of mature oaks under field conditions, and support the previously detected association between presence of P. quercina in the rhizosphere and decline of oak stands in southern Sweden [23]. The association between root damage and severe defoliation of the tree crown may be a consequence of reduced C assimilation as a result of pathogen infection.…”

“…Phytophthora quercina was found to cause root infection in oak seedlings, in artificial soil mixtures as well as in acid forest soils, with subsequent necrosis and die-back of the root systems [21,22]. A weak association was also found between the occurrence of P. quercina and the vitality of mature oak stands [23].…”

Notes on some Phytopythium and Pythium species occurring in oak forests in southern Poland

“…Similar relationships have been revealed for soil-borne Phytophthora spp. in several European countries [10][11][12]26,27].…”

Oak decline in a southern Finnish forest as affected by a drought sequence

“…Thus, the reasons are related with several biotic and abiotic factors, and are frequently a combination of different severe determinants (e.g. Wargo, 1996;Gibbs and Greig, 1997;Thomas et al, 2002), partly with site-specific causes (Jung et al, 2000;Jönsson et al, 2005).…”