Two concentric circles of cedar trees in a forest in Nichinan, Miyazaki Prefecture, were created in an experiment into tree density and growth. Trees planted on the outermost circle were the tallest because of the greater space between each tree. (Video footage by Kengo Hiyoshi)

NICHINAN, Miyazaki Prefecture--Two “crop circles” found in a forest here in southern Kyushu were created not by extra-terrestrials or pranksters but by tree-studying scientists 40 years ago.

The researchers were conducting an experiment designed to look into the growth of local Obi-sugi cedar trees.

According to officials of the southern Miyazaki district forest office who oversee the forest, 720 cedar trees were planted in 1974 in concentric circles. Each circle was composed of 36 trees, and the distance between the trees increased with each outer circle.

The aim of the experiment was to look into the relationship between tree growth and planting density to determine the best way to produce lumber to build homes.

Forest office staff said the concentric circles made it easier to observe the cedar trees in comparison to the other shapes in which the trees were planted.

For many years, observation of tree growth was done by walking into the forest. But when drones were first flown over the forest in 2016, staff members realized that crop circles had been created.

The experiment found that trees in the outermost circle grew to heights of about 20 meters, while those in the circle nearest the center were only 15 meters tall. The finding overturned accepted wisdom that tree density had no effect on tree growth.

The initial plan was to cut down the experimental forest in fiscal 2023. But because of its value as a tourism resource, a decision has been made to preserve the circles in their present condition.