Phytophthora root disease: a new threat for cork oaksat Doñana National Park (south-western Spain)

Abstract: The cork oak is an emblematic species of great ecological value in the ecosystem‘stabilized sands’ at Doñana National Park (south-western Spain). The current oak populationmainly consists of big scattered individuals representing only a 10% of the forest that occupiedthe area three centuries ago and which was devastated by massive cutting. After the protection ofthe area as Biological Reserve forty years ago, all silvicultural practices such as cutting, pruningand cork extraction ceased. However, the population of mature trees is suffering a quick declinethat threatens their survival. The main menace to the survival of cork oaks comes from the highdensity of herbivores (deer, wild boar, cattle, horse) which eat almost all of the acorns andprevent young plants to grow and replace old trees. Additionally, a significant number of oaks arefrequently occupied by a nesting colony of wading birds (storks, herons, spoonbills). These treesshow signs of stress (defoliation), and eventually die much faster than trees not occupied. Finally,we detected a new problem: the sudden decline of trees, which may die within a few monthsindependently to the presence of nesting birds. Phytophthora cinnamomi has been consistentlyisolated from roots and rhizosphere of these trees and an important increment in the number andsize of these foci is expected. In this way, proposals to monitoring the affected trees andpreventive application of phosphonates by trunk injection have been exposed to the Parkauthorities.