Tuohiköysi is a rope braided from birchbark. Birchbark (tuohi)was once an essential part of Finnish household economics. It was used to make shoes, backpacks, baskets, and kitchenware, among other things Article concerning items made of birchbark here (in Finnish, great photos).
Birch ropes were especially handy for nuottakalastus, a type of seine fishing that would often involve the whole village, neighbors cooperating to pull the net to shore. Tuohiköysi was well-suited for this purpose since it floats and does not waterlog easily.
The segment of rope in the following pictures is at least 200 years old. The tuohiköysi fell out of use in Finland after the introduction of rope made from hemp or sisal.