2023-09-23 05:17:05
Published23. September 2023, 07:17
Indian Summer: Fight for survival – that’s why leaves turn yellow here and red in the USA
Summer is slowly giving way to autumn: the first leaves are falling. And what’s still hanging turns yellow. At least with us. Things look different overseas. That’s what lies behind it.
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Autumn in this country is not as colorful as in the USA. (Pictured: Boston’s Brighton neighborhood during Indian Summer)
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Even our deciduous trees in autumn cannot keep up with the splendor of the colors of the Indian summer in Canada.
Nova Scotia Tourism
In our latitudes, the leaves of deciduous trees also change color,…
20min/Community
That’s what it’s regarding
Autumn puts an end to the green of deciduous trees.
The color the leaves then take depends on the location of the trees.
While they turn bright red tones in the United States, Canada and parts of Asia, here the foliage tends to turn yellow. That was not always so.
Here you can find out what the ice ages have to do with it.
The battle for life and death is rarely as beautiful to see as with deciduous trees in autumn. Because before they finally shed their leaves, they first change color. In our latitudes, green turns yellow. In North America, however, the autumn leaves shine in different shades of red. The so-called Indian Summer (see box) is world famous.
Indian Summer
Indian Summer is the name given to an unusually dry and warm period of weather in late autumn on the North American continent. Typical of this are the bright blue sky, the warm weather and the particularly intense leaf coloring in the deciduous and mixed forests.
Indian Summer occurs in the United States exclusively in an area that extends from the Mid-Atlantic states north to New England and westward across the Ohio Valley and the Great Lakes region, the Midwest of the United States, the northern part of the Great Plains and Canada pulls. All areas where temperatures are well below freezing at night and there is plenty of sunshine during the day. However, Indian Summer is mostly associated with the New England states and Canada.
Why is it a matter of life and death?
The deciduous trees are preparing for winter. If they didn’t do this and kept leaves even in the cold season, they would dry up sooner or later. Because they evaporate a large part of the water that the roots absorb through their leaves. In the cold season, the roots can draw less and less water from the soil. If they released the little water they absorb in winter through their leaves, the tree would no longer have any strength.
How do the trees know it’s fall and they need to prepare?
You can tell by the temperatures and the fact that the days are getting shorter. Then they receive less light, which leads to a decline in photosynthesis. The trees use the energy of the sun’s rays and the carbon dioxide in the air and water to produce glucose and oxygen. The green chloroplasts make this possible. They contain chlorophyll, which turns the leaves green.
But as the days get shorter, the trees break down the chlorophyll and store it in roots, branches and trunks. Then the pigments in the leaves that would otherwise be displaced by chlorophyll come to the fore.
Why do our leaves turn primarily yellow and in the USA they turn red?
In preparation for winter, deciduous trees around the world break down the green of their leaves and then store it in branches and trunks until spring. But while the leaves in North America – and also in East Asia – produce the red pigment anthocyanin and turn red, the European leaves do not do this. Without the green leaf, you are left with the yellow pigment that has always been in the leaf.
Has it always been like this?
No, this difference did not exist 35 million years ago. Researchers from the universities of Haifa and Eastern Finland came to this conclusion in 2009. Like the team in the journal «New Phytologist» writes, all trees at that time produced anthocyanin. The red dye deters insects that want to eat the leaf proteins.
Why is that no longer the case today?
This was ensured by several ice ages. During this time, plants and animals in North America and East Asia – including insects – retreated south to warmer climes. There they survived the cold periods and spread once more following they ended, where they still exist today.
In our latitudes it was not possible for them to escape south. While in the USA and East Asia the large mountain ranges run from north to south, in our country the Alps form an insurmountable barrier from east to west. The plants and animals had to stay and freeze to death. When the ice ages were over, new trees emerged. And because there were no predators, they no longer needed to turn red.
In the end the leaves fall completely – how does that work?
In principle, this happens en passent: When the trees break down the chlorophyll – and other nutrients such as protein – in autumn, they also cut off the water pipe and the area between the branch and the leaf stem becomes corked. This causes the leaf to become loose and easily blown away by the wind.
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