Common cypress (Cupressus sempervirens L.) is a significant element in the Mediterranean region and Tunisia, present in both forest and agricultural windbreak for centuries. However, in recent decades, common cypresses in certain Tunisian areas have experienced dieback and mortality. Presently, many common cypress windbreaks display severe damage, possibly due to fungal pathogens. In the summer of 2022, a field survey was conducted in three regions of northern Tunisia (Menzel Bouzalfa, Morneg, El Alia) to investigate diseased common cypresses and identify the responsible pathogens: 935 trees belonging to 14 windbreaks were surveyed. Branches and twigs samples were collected from 47 affected trees showing symptoms such as yellowish-brown foliage, necrotic lesions, cankers, resin exudation and diebacks. Initially, isolates were morphologically characterized, and representative isolates were further analyzed using molecular methods. Using the traditional culture method, 41 fungal species associated with common cypress dieback were identified. Pathogenicity tests were performed on eight fungal species known as possible pathogens: Phaeobotryon cupressi, Diplodia cupressi, Diplodia olivarum, Diplodia pseudoseriata, Seiridium cardinale, Pestalotiopsis funereoides, Neofusicoccum mediterraneum, and Didymosphaeria variabile. Phaeobotryon cupressi, D. cupressi, and S. cardinale displayed the highest pathogenicity, followed by P. funereoides and D. olivarum, which caused smaller lesions. With the exception of D. cupressi, all of the identified fungal pathogens are being reported for the first time in Tunisia or in common cypress. The pathogenic action of most of the isolated fungi could have been enhanced by the prolonged droughts that have repeatedly occurred over recent years.

The Numidian cypress (Cupressus sempervirens var. numidica, C. numidica hereafter) is a rare, almost unknown, endemic taxon of Tunisia whose conservation has long been hampered by human activities, taxonomic uncertainty and limited ecological knowledge, with only 64.33 ha of its populations remaining. Although recent genetic studies have confirmed its native status and long-term isolation, detailed information on its distribution, population structure and threats remain lacking. This study provides the first comprehensive assessment of C. numidica across its remaining range. Field surveys revealed that the species persists in only three small, fragmented forests, Bou Abdallah, Sidi Amer, and Dir Satour, covering a total of 64.33 ha. Soil analysis revealed some differences among sites, with Bou Abdallah showing higher clay content and Dir Satou exhibiting the highest levels of nitrogen, organic carbon, Olsen P, and available Mn and Mo. Climatic analyses indicate a semi-arid Mediterranean environment with pronounced summer droughts and a clear warming trend. Trees showed widespread damages, due to intensive grazing, tree cutting, crown dieback (drought), and pest and pathogen attacks. Natural regeneration was limited, and the condition of affected trees ranged from moderate to severe, with Bou Abdallah showing the highest levels of degradation. Notably, the severe fungal pathogen Seiridium cardinale, causal agent of cypress canker, was detected on C. numidica for the first time, highlighting an urgent conservation concern. Our results point to a staged conservation approach over time. In the immediate term (within 1 year), urgent monitoring and management of S. cardinale is needed. In the short term, efforts should focus on protecting carefully selected areas, about 5–10 regeneration microsites per forest, from grazing to support natural regeneration, reduce ongoing soil degradation, and establish clonal and seed-production plantations along with long-term seed storage. In the long term, the survival of C. numidica will only be possible with the active involvement of local communities, through awareness campaigns, adapting traditional practices such as gdel, and developing small-scale ecotourism that provides sustainable livelihoods while reinforcing support for conservation.