The importance of artefacts of ancient land use on plant communities in Meerdaal forest, Belgium

On a landscape level, former land use is a structuring element of plant communities of recent and ancient forest patches. However, ancient land use has been recently identified to affect plant communities within ancient forests. An ancient holloway, i.e., a U-shaped sunken road, embedded in the Meerdaal forest was used to establish whether microtopographical changes brought about by the former road use would structure the forest vegetation and seed bank. Seven transects were set out perpendicular to the holloway over a one kilometer stretch, to test whether the sunken road would locally shape the patterns in abiotic conditions, vegetation and seed bank. Soil pH was significantly higher within the holloway, which was reflected in a higher plant cover, ancient forest and overall species richness. Vegetation composition was altered by the road microtopography, though secondary to a prevailing fertility gradient with distance along the holloway. While seed bank characteristics did not differ between road and non-road plots, seed bank composition did vary according to the microtopography. However, the extant vegetation caused the observed seed bank pattern. The holloway shapes understory community patterns in vegetation and seed bank. As the sunken road cuts into deeper calcareous soil layers at the bottom of the road, this gave way to differential acidification (different buffer ranges) in function of the microtopography, allowing the persistence of favorable growth conditions within the holloway. Hence, these conditions allow the survival of ancient forest species within the road in a forest matrix made increasingly unsuitable through severe acidification