| Abstrakt: |
Oak decline is not attributed to a single factor but rather arises from a complex process involving several factors, such as environmental areas, climate change, insects, and pathogens. Weakened trees by predisposing abiotic factors, mainly water deficit, are highly vulnerable to fungal attacks. Notably, pathogenic fungi assume a crucial role in this process, contributing to tree mortality. Additionally, defoliators are the insects most frequently associated with oak decline. In Tunisia, oak forests have experienced decline associated with outbreaks of defoliating insects and fungal manifestations following severe drought episodes. This oak dieback dates back to the 1950s. Subsequently, another severe dieback was observed in the 1990s, particularly pronounced in cork oak forests. As a consequence, the cork oak forests areas have significantly decreased by 40,000 ha in 40 years (1952–1992), indicating a decline rate of 1000 ha a−1. Later on, a significant decline has been noticed since 2020 and has become increasingly widespread since 2023 in the nearby cork oak forests, requiring an emergency response. The outbreaks of defoliating insects and fungi further exacerbate the situation. Their combination with silvicultural mismanagement and a lack of oak regeneration give rise to a serious threat to oak forests. In this review, we describe the dynamics of insects and pathogenic fungi in Tunisian oak forests, considering their perceivable role in the decline detected in Tunisia during the last few years. Consequently, Lymantria dispar(Linnaeus, 1758), Tortrix viridana(Linnaeus, 1758), Operophtera brumata(Linnaeus, 1758), Erannis defoliaria(Clerck, 1759), Orgyia trigotephras(Boisduval, 1829), Biscogniauxia mediterranea(Kuntze, 1891), Pestalotiopsis biciliata, Diplodiaspp.and Alternariasp. species have been reported as the most common pests in oak forests. These pests have demonstrated an expansion in both their geographic and host distribution over the years, likely due to their phenotypic plasticity allowing them to overcome the challenges posed by climate change. Due to the complexity of the decline etiology involving pests and climate, it is difficult to define suitable control strategies. However, the primary focus should be on planting more resistant oak varieties to mitigate threats posed by insects and fungi. |
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