Can Scots pine (Pinus sylvestris L.) forests harbour natural regeneration of European ash (Fraxinus excelsior L.)?

The proportion of European ash (Fraxinus excelsior L.) stands decreased rapidly over the last thirty years. The
highest declines are recorded in fertile ash-dominated habitats. Thus, a comprehensive understanding of successful ash establishment is needed across broader habitat conditions. Therefore, we aimed to investigate ash
natural regeneration in pine-ash forests and adjacent pine-dominated forests without ash in overstory but with ash
regeneration. We assessed the effects of soil environment, soil moisture, browsing, ash regeneration density and
its health status.
The most limiting factors of ash regeneration were low soil moisture, high soil acidity, and the increase of pine
proportion. We noted the highest densities only for ash regeneration of up to 0.6 m height growing on moderately
acidic soils in pine-ash forests. Our models showed a low number of saplings damaged by ash disease. Instead, we
revealed a high proportion of drought-damaged saplings without dieback symptoms. The highest browsing occurred
within pine-ash forests with a lower proportion of pine trees in overstory. Despite theoretically unfavourable soil
conditions, we state that pine-ash forests can harbour ash regeneration and may allow for its natural and assisted
recolonization. In contrast, within pine-dominated forests located in the vicinity of pine-ash stands, the successful
regeneration of ash is negligible due to high soil acidification and low moisture.