NAZIs planted trees of contrasting colour in the shape of swastikas in various forests around Germany.

The forest swastika was a patch of carefully arranged larch trees covering a 3,600 m2 (4,300 sq yd) area of pine forest near Zernikow, Uckermark district, Brandenburg, in northeastern Germany. The reason behind the planting of the trees is unclear, but it has been suggested that it was laid out in 1937 by locals to prove their loyalty after a businessman in the area was denounced and sent to a concentration camp by the Nazi Party for listening to the BBC, or that a zealous forester convinced local Hitler Youth members to plant the trees in commemoration of Adolf Hitler’s birthday.

For a few weeks every year in the autumn and in the spring, the colour of the larch leaves would change, contrasting with the deep green of the pine forest. The short duration of the effect combined with the fact that the image could only be discerned from the air and the relative scarcity of privately owned aeroplanes in the area meant that the swastika went largely unnoticed after the fall of the Nazi Party and during the subsequent Communist rule. However, in 1992, the reunified German government ordered aerial surveys of the state-owned land. The photographs were examined by forestry students, who immediately noticed the design.

Wikipedia