Data on the number of occurrences of specific tree-related microhabitat (TreM) types (classified according to Kraus et al. 2016) recorded on 1,200 sample trees, including invasive Acer negundo and five native tree species.

Invasive tree species can substantially alter forest biodiversity, structure, function, and ecosystem services. However, their role in supporting tree-related microhabitats (TreMs) remains largely unexplored. Acer negundo L., a North American tree species now widespread in European forests, is characterized by rapid growth, multi-stemmed architecture and irregular branching: traits that may confer a high potential for TreM formation. We assessed TreMs on 1,200 trees differing in breast height diameter (DBH), including A. negundo and five native species (Acer platanoides, Betula pendula, Carpinus betulus, Quercus robur, Tilia cordata) in secondary oak–hornbeam forests of the Białowieża Forest (NE Poland). Using redundancy analysis and mixed-effects models, we revealed that TreM diversity indexes increased with DBH in all species, with A. negundo supporting overall TreM richness comparable to native trees. The occurrence of specific TreMs (e.g., bark pockets, dendrotelms, microsoils, exposed heartwood, or witch’s brooms) appeared at lower DBH in A. negundo than in native trees, demonstrating the importance of this invasive tree in creating new microhabitats even on small trees. Other identified TreMs occurred on A. negundo at rates similar to native trees, suggesting that it can provide ecosystem services typically associated with larger trees or mature forests. Our findings indicate that A. negundo increases structural heterogeneity of the forest by promoting the early development of several TreM types typically associated with larger or older trees. In secondary and disturbed forests, this species may partially compensate for the scarcity of large-diameter native trees by providing TreMs at smaller DBH, with direct implications for the retention of habitat structures during forest regeneration. Management strategies should therefore explicitly account for tree size and TreM availability rather than species identity alone when evaluating the consequences of A. negundo invasion in secondary forests lacking large native trees. Management decisions concerning this invasive species should therefore weigh TreM provisioning against its known invasive impacts at the stand scale.