An overview of the major threats affecting European saproxylic beetles is shown in Figure 3. Logging, tree loss and wood harvesting are by far the greatest threats to both threatened and non-threatened saproxylic beetles, affecting more than half the species (54.5%, 375 species), including 76 threatened species. Tree loss refers to the threats of tree age structure gaps, loss of ancient and veteran trees, degraded landscapes that are unfriendly to tree growth, and indiscriminate felling for spurious health and safety reasons. This highlights the importance of European forests and other landscapes with trees for the continued survival of these deadwood-dependent species.
A large number of saproxylic beetles are dependent on ancient and veteran trees, especially those species developing in decaying heartwood and accumulations of wood mould in the resulting cavities. In Europe, large hollow trees have become increasingly rare due to land management procedures (e.g., logging, felling for health and safety reasons). Thus, the populations of saproxylic organisms associated with this microhabitat are undergoing a decline. This decline is of special importance for several species of beetles belonging to the Elateridae, Scarabaeidae, Staphylinidae and Tenebrionidae, since these are the largest and most ecologically important insect families living in this microhabitat.
Throughout Europe, the presence of deadwood has historically been considered as a sign of neglect and poor forest management. As a result, some forests are still “cleaned” of fallen logs and standing dead trees, which can lead to the disappearance of saproxylic beetles from the area. Old trees in urban environments are also often cut down due to public safety concerns. However, in many countries the importance of deadwood is being increasingly acknowledged and best practice management now highlights the importance of having landscapes and forests with a diverse tree age structure, native tree species, and a sufficient number of mature and decaying old trees in different stages of aging. Ancient tree inventory projects are taking place in several European countries, such as the UK, Italy and Romania.
Recruitment of new trees to replace disappearing veteran trees is very low. Thus, despite a current assessment of Least Concern, certain species require urgent conservation action. Even if the current populations are still strong, halting the decline of European veteran trees and promoting the recruitment of new trees - which will take hundreds of years to grow - is critical to ensure their long-term survival.
In the EU, the outstanding conservation value of semi-open wood pasture systems with veteran trees is currently neither specifically recognised in the Common Agricultural Policy, nor in annex I of the Habitats Directive. Even within Natura 2000 sites specifically designated for wood pastures or saproxylic beetles, eligibility rules for CAP payments are promoting management practises that are leading to a transformation of wood pastures into either woodland or grassland, thereby destroying the essential vegetation mosaic beetles require.
Urbanisation and tourism development is the second most important threat, affecting 9.6% of saproxylic beetles (66 species), of which 30 are threatened. Habitat loss due to infrastructure construction is particularly important in the Mediterranean coastal regions due to tourism development. New motorways also pose a significant threat, since they lead to an increase in the fragmentation of tree landscapes.
An increase in the frequency and intensity of wildfires, as well as wood and pulp plantations are the next most important threats, impacting 61 and 35 species, respectively. Other threats include arable farming, pollution and invasive alien species (Figure 3). Climate change is also a potential major threat, but assessment of impacts on saproxylic beetles is extremely challenging and there is still limited understanding and appreciation of the issue. The threats for a total of 182 saproxylic beetles remain unknown, reflecting the need for more field work and monitoring.
Figure 3. Major threats to saproxylic beetles in Europe.