Effects of tree characteristics and climatic conditions on gall midge abundance on European beech (Fagus sylvatica L.)

Asaconsequence ofclimate change and damage toconiferous forests, European beech (<i>Fagus sylvatica</i> L.) isthe preferred plant species for forest restoration inCentral Europe. European beech isgenerally regarded aspest-resistant. However, its vulnerability tosecondary pests, for instance, gall-forming midges, may increase with environmental stress such aslong drought periods. Weanalysed the abundance oftwo gall-forming insects, <i>Mikiola fagi </i>and<i>Hartigiola annulipes</i>, onEuropean beech at26 forest sites across the Czech Republic, spanning diverse climatic and environmental conditions, using generalised linear mixed models toevaluate the effects ofabiotic factors and host tree characteristics. The results revealed that <i>M. fagi</i> was more abundant onyounger trees, instands with lower canopy closure, and under warmer spring conditions. Incontrast, the abundance of<i>H. annulipes </i>declined indrought-affected areas. These patterns demonstrate species-specific responses ofgall midges tohost tree characteristics and climatic variables, suggesting that climate change may favour higher <i>M. fagi</i> abundance. Accordingly, our findings support the establishment of young beech stands under higher canopy closure, for example, beneath the shading of mature trees.