Data from: Site- and tree-related factors affecting colonization of cork oaks Quercus suber L. by ambrosia beetles in Tunisia

Key message: Ambrosia beetles are emerging globally as important agents of
tree death and decline. In this work, we observed highly variable attack
intensity by ambrosia beetles in cork oak stands in Tunisia. A correlation
between the proportion of infested trees and average temperature was
found. Tree diameter and tree phytosanitary variables further contribute
to the attack densities of ambrosia beetles. Results can be relevant for
preventive measures aiming to conserve this natural forest heritage.
Context: Cork oak woodlands comprise a unique Mediterranean ecosystem
supporting rich biological diversity and providing multiple services. A
decline of cork oak forests has been observed in several regions of the
Mediterranean Basin in the last four decades, which can be related to
climate change, novel biotic agents, and changes in management practices.
The ambrosia beetles have been one of the major biotic agents associated
with cork oak decline, mostly in the western Mediterranean. Aims: Assess
the presence and attack densities of ambrosia beetles in cork oak Tunisian
forests. Methods: A total of 15 sites located in North Western of Tunisia,
comprising 729 sample trees were evaluated. Using generalized linear
models, the presence and density of ambrosia beetles’ holes were related
to tree and site variables. Variables related to climate, tree
(dendrometric parameters, debarking intensity) and biotic agents were
examined. Results: The proportion of trees attacked per site varied from 0
to 100%; in four sites it exceeded 50%. At the site level, the average
temperature and tree diameter were the main variables explaining the
proportion of attacked trees. Sites with warmer climates showed higher
incidence of ambrosia beetles. At the tree level, the presence of attacks
increased with tree diameter and concomitantly with intensity of
debarking, as well as the presence of tree trunk cavities. Conclusion: The
presence and density of insect attacks were related to tree diameter, area
of debarking, and phytosanitary conditions. However, 19% of the trees
attacked by ambrosia beetles had no signs of other biotic agents or
decline. At the site level, attack rates increased with temperature and
tree diameter. A warmer climate may change insect behavior from that of a
non-agressive pest to that of an agressive bark beetle. Adaptive forest
management practices are needed to reduce infestations.