Clone stands of bracken fern (Pteridium aquilinum (L.) Kuhn.) wood small reed (Calamagrostis epigeios L.) and lily-of-the-valley (Convallaria majalis L.) are often partly split into two by the road, but often encountered also unilaterally on the roadside in the shape of a semicircle. The unilateral stands can be at times 20–30 m wide and they are sometimes solitary stands of the species. A method to define the age of the solitary stands of six plant species including bracken, wood small reed and lily-of-the-valley was developed in a series of earlier studies.
These stands can be used to define the time the road was built. Clones that are bound by the road unilaterally are younger than the road. If there are several unilateral clones and they are of different sizes, the road is older than the largest clone. When the road is skirted bilaterally only by clones divided by the road, it is younger than the smallest clone. When there are by the road side both unilaterally delimited clones and clones split by the road, the age of the road comes in the range of time determined by the age difference between the largest unilateral and smallest bilateral clone.
The PDF includes a summary in English.