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Chapter 9
Coping with Pests and Diseases Manuela Branco and Ana Paula Ramos
As mentioned in previous chapters, cork oak trees are vulnerable to several kinds of biotic agents in various ways and at all stages of their lives. Vertebrates, including large mammals and rodents, as well as dozens of insects and microbial pathogens all affect cork oak seeds and seedlings and, consequently, the natural regeneration and afforestation of cork oak woodlands (see Chapters 10 and 12). Mature stands of trees are also subject to a wide variety of pests and diseases, with profound implications for tree vigor, mortality, and productivity of individual trees and entire stands or populations. At moderate to high levels of incidence, the effect of biotic agents may trigger the decline of ecological functions of this type of forest and endanger its sustainability. In particular, tree mortality, crown cover reduction, and reduced natural regeneration may directly influence the floristic composition of the herbaceous and shrub layers of vegetation, as well as fauna and the overall hydrologic regime of the woodland. The sociological and economic importance of herbivores, insect pests, and diseases can also be high because they can reduce the quantity and quality of cork produced, with consequent impact on income for landowners and employment opportunities for local people. A reduction in acorn production and seedling mortality, affecting both natural regeneration and restoration success, also has adverse economic impacts with respect to animal production, stand age structure, tree density, and the eventual costs of replanting cork oak trees. Until recently, pests and diseases did not markedly affect cork oak, except for periodic outbreaks of defoliator insects. However, in the last few decades a dramatic decrease in holm oak and cork oak regeneration and an increase in both trees’ vulnerability to pests and diseases have been confirmed throughout the western Mediterranean (e.g., Gallego et al. 1999; Sousa and Debouzie 103