New indicator species for associations within mesotrophic oak-hornbeam forests in Poland

• Research on oak-hornbeam forests reveals new pools of indicator species. • Stellario-Carpinetum is distinguished by a large group of mosses. • Other oak-hornbeam phytocenoses by high percentage of common forest species. • The current status of oak-hornbeam forests in Poland is changing. • Mosses can be highly valuable for phytosociological studies. The following oak-hornbeam plant associations have been described from Poland: Tilio - Carpinetum (TC), Galio-Carpinetum (GC) and Stellario - Carpinetum (SC). Our findings indicate that all are distinguished by a relatively high percentage of common forest species, particularly the first two. The study is the first to identify the following species as indicator species, based on SOM analysis and IndVal index: e.g. Brachythecium velutinum , Cirriphyllum piliferum , Lepidozia reptans , Mnium hornum , Plagiomnium undulatum and Brachypodium sylvaticum for SC; Ajuga reptans , Dryopteris filix-mas , Equisetum pratense , Frangula alnus , Galium odoratum , Hepatica nobilis , Luzula pilosa , Maianthemum bifolium , Milium effusum , Plagiomnium affine , Pulmonaria obscura for TC, and Asarum europaeum , Anemone ranunculoides , Corylus avellana , Galeobdolon luteum , Geum urbanum , Mercurialis perennis , Stellaria holostea and Ulmus laevis for GC. However, for Stellario-Carpinetum , our findings indicate a large pool of bryophytes that have never been considered as bioindicators. Additionally, our research indicates that while the main species composition gradient of broad-leaved forests is related to soil moisture, temperature also plays a significant role in creating a Stellario-Carpinetum – Tilio - Carpinetum gradient. The current status of oak-hornbeam forests in Poland is intriguing; our research indicates that supplementing vascular plants with bryophytes in research could change the traditional syntaxonomy of oak-hornbeam forests in Central Europe.