Tamara Corcobado

Combined effects of soil properties and Phytophthora cinnamomi infections on Quercus ilex decline

AimsThe importance of soil properties as determinants of tree vitality and Phytophthora cinnamomi root infections was analysed.MethodsThe study comprised 96 declining stands in western Spain, where declining and non-declining holm oak (Quercus ilex L.) trees were sampled. Soil properties (soil depth, Ah horizon thickness, texture, pH, redox potential, soil bulk density and N-NH4+ and N-NO3− concentrations) and P. cinnamomi infections were assessed.ResultsTree mortality rates increased with low soil bulk densities, which were also associated with more P. cinnamomi-infected trees. Occurrence of infected trees was higher in fine textured soils and in thick Ah horizons. Fine textured soils favoured trees, but with the presence of P. cinnamomi their health status deteriorated. Soil under declining trees had higher N-NO3−/N-NH4+ ratio values than under non-declining trees. Additional soil properties changes associated to grazing were not related to decline and P. cinnamomi infections.ConclusionsThe implications of P. cinnamomi in holm oak decline and the influence of soil properties as contributors to pathogen activity were demonstrated. Fine soil textures and thick Ah horizons, usually favourable for vigour and vitality of trees growing in the Mediterranean climate, were shown to be disadvantageous soil properties if P. cinnamomi was present. Fine soil textures and thick Ah horizons are frequently related with higher levels of soil moisture, which increase the inoculum of the pathogen and favours root infection. Grazing does not seem to be directly linked to Q. ilex health status or P. cinnamomi root rot.

Early survival of Quercus ilex subspecies from different populations after infections and co-infections by multiple Phytophthora species

Forests in Europe are threatened by increased diversity of Phytophthora species, but the effects of the simultaneous presence of these pathogens on trees and the ecological consequences of their coexistence are unknown. This study aimed to explore variation in early survival of Quercus ilex to Phytophthora infections and assess interactions between Phytophthora species when trees are co-infected separately in time. Three Phytophthora species (P. cinnamomi, P. gonapodyides and P. quercina), seeds from 16 populations of Q. ilex (from both ballota and ilex subspecies) and two infection times were used as sources of variation in two experiments. The influence of the Phytophthora species, Q. ilex subspecies and populations on plant germination and survival were analysed using generalised linear mixed models and survival analysis techniques. Germination rates were not influenced by Phytophthora spp. (P = 0.194) but by the subspecies and populations of Q. ilex (P < 0.001). In Phytophthora infested soils, acorns of Q. ilex ssp. ilex germinated at higher rates than acorns of Q. ilex ssp. ballota. In contrast, plant survival was strongly influenced by Phytophthora species (P < 0.001), but not by the subspecies and populations of Q. ilex. Reduced and delayed seedling mortality were observed if a less virulent Phytophthora species infected plants prior to infection by a more virulent Phytophthora species, e.g. plants infected first by P. cinnamomi died at higher rates and earlier than plants infected first by P. gonapodyides and P. quercina (P = 0.001). The results help to explain oak decline syndrome and the lack of natural and artificial regeneration of Q. ilex forests. The lack of interspecific variability of early survival to Phytophthora spp. discourage direct sowing as a strategy in artificial reforestation programmes. Large, thick seeds that give plants rapid growth are advantageous traits if soils are infested with Phytophthora spp. This article is protected by copyright. All rights reserved.

Invasive forest pathogens in Europe: Cross-country variation in public awareness but consistency in policy acceptability

Political action can reduce introductions of diseases caused by invasive forest pathogens (IPs) and public support is important for effective prevention. The public’s awareness of IP problems and the acceptability of policies aiming to combat these pathogens were surveyed in nine European countries (N = 3469). Although awareness of specific diseases (e.g., ash dieback) varied, problem awareness and policy acceptability were similar across countries. The public was positive towards policies for informational measures and stricter standards for plant production, but less positive towards restricting public access to protected areas. Multilevel models, including individual and country level variables, revealed that media exposure was positively associated with awareness of IP problems, and strengthened the link between problem awareness and policy acceptability. Results suggest that learning about IPs through the media and recognizing the associated problems increase policy acceptability. Overall, the study elaborates on the anthropogenic dimension of diseases caused by IPs.