Birch Alley in Uppsala, Sweden

As part of a former botanical garden, this alley of birches was planted in the 1980s. But these are not just any birches, it is a collection of birches from all over Sweden from the south to the north, and in the alley, they are also ordered by their latitude of origin.

In autumn, these trees still shed their leaves at different times. This is because the shedding of leaves is regulated by the length of the night and trees from different latitudes have adapted to different night lengths as a trigger signal.

One can see that winter is approaching when the northern end of the alley is already naked and brown, while the southern end still has the most leaves left.