Water-filled tree holes are islands of aquatic communities found within forests. The macroinvertebrates found in these holes are limited to one tree hole during their juvenile stage, however they are able to disperse during their adult stage. Forest management practices alter dominant tree species and age structure, which we expect will have impacts on the abundance of water-filled tree holes and the tree hole communities. We mapped all water-filled tree holes in 75 1-hectare plots in three different regions of Germany under different forest management. In order to look at the macroinvertebrate communities 128 tree holes were sampled and abiotic characteristics were measured (pH, dissolved oxygen, volume, water volume, height and debris).
Using a forest management index we found that increased forest management intensity has a negative influence on the abundance of tree holes, however, the influence on the abundance or species richness of the insect larvae inside was not as clear. While we did not find an influence of tree hole size and total water volume on the insect communities, higher amounts of debris accumulation had a positive influence on insect abundance and tree holes within forests of lower management intensity had a higher accumulation of debris. Additionally, higher abundances of larvae were found in tree holes at greater heights. We are still growing in understanding of the role of tree holes in ecosystems and their importance. Care should be given to protect these small habitats, as they are a water source dispersed throughout forests and many of the organisms found in tree holes require these habitats during their juvenile stage. Although insect abundances within tree holes was not clearly influenced by forest management intensity, we can expect that decreased habitat availability will decrease overall abundances within forests.