Red, yellow, orange and ochre — the leaves of the maple, oak and alder trees in the forests of New England literally explode with colour in the Indian summer. But why are the colours of the leaves that create the "fall foliage" so intense in this part of the North-east USA? The answer is quite simple. In Western Europe, our forests containing around 50 different tree species also become a blaze of colour. But the forests of New England are home to more than 800 species of tree, all of them ensuring that the forests glow like flames all through the Indian summer. Finding the perfect time to observe the unique interplay of the colours of the trees in person amidst the fading sunlight is not easy.
The leaves begin to change colour at the end of September and can be seen in some places until the middle of November. Every year, large numbers of "leaf peepers" wait for the absolute perfect moment to enjoy the spectacle of the colours in the "peak foliage". The exact moment is hard to predict, because a number of different factors come together to determine when the different colours are at their brightest. The full splendour of the autumn leaves may be earlier or later depending on the length of the days, how much rain falls, whether the sugar content in the leaves is high or low, and the temperatures. This special time usually only lasts a few days. The Department of Energy and Environmental Protection posts updates on the progress of the Indian summer on its website to make sure that nobody misses out. A special "fall foliage hotline" is also available 24 hours a day to keep foliage fans updated on the changing colours. The Indian summer can be seen first in the north of New England before gradually spreading further south. For example, it may begin in Maine by the last week in September, before the forests of New Hampshire and Vermont change colour in the coming days and weeks, until finally the Indian summer reaches Connecticut and Rhode Island further south.
Why is it called an "Indian summer"?
There are a number of different explanations regarding the origin of the phrase "Indian summer" so we still cannot say for sure where the term comes from. One of these phrases comes from Indian mythology. According to Indian or Native American legend, the blood of killed bears seeps into the soil and travels through the roots into the leaves of the trees, causing them to turn red. Another explanation is based on a different Indian tradition, as they were said to have used late autumn as their major hunting season, because the mild temperatures at that time of year bring wild animals out of their hiding places again. But the phrase may also have come from seafarers, who were supposed to have finished loading their ships by the autumn to begin their journeys towards the Indian Ocean.
And why do leaves change colour?
Every amateur gardener must have asked themselves this question at least once. The rich green colour of the leaves in summer is caused by the leaf pigment chlorophyll. When the days get shorter and the temperatures start to drop, the trees sense that it is time to get ready for winter. Why is this? In winter, trees would lose a lot of their water through their leaves. But if the ground is frozen, trees would find it very difficult to access enough of the moisture they need. The solution is for the trees to shed their leaves in winter to reduce the amount of moisture they lose. The chlorophyll in the leaves is therefore broken down and stored in the roots as "building material" for the next spring. Once the chlorophyll has been removed from the leaf, other leaf pigments emerge, which had previously been masked by chlorophyll. This results in the unique change in colour seen in leaves and trees. And why do the leaves ultimately fall? As soon as there is no more chlorophyll available in the leaves, a layer of cork develops between the stalk and the base of the leaf, which seals off the leaf scar to come. Once this is in place, there is nothing left to hold the dead leaves on the tree. The autumn winds then blow them from the tree canopy and they fall to the ground, where they decay to form valuable humus.
Every year, this thorough yet fascinating process makes sure that nature can protect itself against the ravages of winter — and at the same time it provides us with the unforgettable sight of a brightly-coloured carpet of leaves.
Foto: © mdbrockmann82