Current issue: 53(4)
The size of the field and the ditching on it as well as the condition of the field at the time of the surrender of Porkkala area (from Finland to Russia) play an important role on how far the natural regeneration of the fields has progressed.
Larger open fields have naturally regenerated only on sides where the surrounding forest can spread the seeds or the thicket of saplings has reached, whereas small parcels of fields have normally been fully forested. Most important species have been e.g. silver birch and pubescent birch, grey and common alders and European aspen as well as pine and spruce. The broad leaved species are dominant.
The PDF contains a summary in Finnish.