​​For a few days every fall, the leaves have the most beautiful colors of the year and people go to photograph them, there is also tourism in the US and Canada to see the leaves. Are leaves falling later due to global warming? What happens to colors in extreme weather years? Why do the leaves have such a wonderful color in autumn?

Luxurious foliage, color tourism and tree stress

In the US and Canada, these days with the most beautiful colors of the trees contribute to a significant increase in tourism, and there are maps of the places where the most beautiful autumn colors are in real time, like weather maps. Hotels charge higher rates for forest-view rooms, and some book rooms months in advance, although it’s impossible to say exactly when (October or November) the beauty will be at its peak. It is estimated that about a billion dollars is spent on this colorful foliage tourism in North America.

Leaf hunting is the search for leaves when they are yellow, red, brown, or dark green, essentially “hunting” for beautiful scenery to “catch” just when they offer the most vibrant colors. America has meteorologists who specialize in predicting the places and times in the fall when the leaves reach their peak color. Computer programs are also used to more accurately predict where exactly the peeping leaves can see the most beautiful colors.

They talk about “paradise for leaves” and about “fireworks” of nature, which can be seen only during the day and with as much light as possible.

A Google search for terms like “Fall Foliage Tracker” or “Find Peak Colors” brings up tons of USA and Canada color maps, detailed by day and location.

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In North America, there are statistics for hundreds of places about the period when trees displayed their most beautiful leaf colors in the past.

Forests “bear the brunt” of the early spring arrival of excessively high temperatures and the late end, in the second half of autumn, of intense heat. It doesn’t happen every year, but it’s happening more and more.

Autumn colors do not have a clear history

Some studies in the US and Canada claim that climate warming has caused the best fall colors to appear an average of a month later than 130-140 years ago. On the other hand, there were many forest fires, so millions of trees in 2023 did not have time to put on any colorful “outfit” in October. Not to mention extreme weather conditions, such as storms that shake trees or knock them to the ground.

The effect of a warming climate on autumn leaf color can vary greatly from region to region and from year to year. There are no clear and complete data.

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The existence of trees has become very difficult due to years full of climatic extremes. Buds can appear very early in spring, but late frosts can occur in the second half of April. Due to the heat and drought in August, leaves may fall, but there may be vegetative recovery in autumn if it lasts long in the heat “post-2023”. The trees then postpone their winter “rest” period, and this dysregulated ecosystem cycle can also mean that the “stress” the trees are under makes them more susceptible to various diseases and pests.

Scientific studies of autumn colors are sporadic and cover small areas, and very few places have extensive historical records of the times of year when the colors were at their most beautiful.

An American naturalist named Henry David Thoreau noticed back in 1860 that the maples in his hometown of Concord, Massachusetts, were the brightest on autumn days. Today, leaves change their most beautiful colors a week or two later than they did 160 years ago, and the fantastic difference has to do with technology, as Harvard University studies leaf colors and their duration with so-called special cameras called “phenocameras.” . With the help of 350 such cameras, the period of maximum leaf color in many areas of Canada and the USA was analyzed:

Other studies in the US say that leaves change color a month later than in 1880, but such a difference cannot be generalized to the whole planet or the whole continent.

The various studies and calculations done to estimate how the moment when the leaves reach their most beautiful color has changed conflict with each other, but agree that it is about 7-10 days later than it was a few decades ago. In Europe, researchers have found that the autumn color season has become shorter in some regions, meaning there are fewer days with the maximum number of beautiful colors.

There are also naturalists who argue that we do not have enough information from such a variety of places to conclude that the period of great colors has changed. They note that the interval varies from year to year by a few days due to climatic factors, but this does not change the average date when the magnificent colors can be seen at their maximum.

When temperatures are higher, photosynthesis takes longer, which means leaves produce more chlorophyll. This can cause the leaves to stay green longer, which can shorten the length of the fall color season.

If the autumn is much cooler than usual, the beautiful colors appear earlier, and in warm autumn years the colors develop later. There is a big difference between different types of trees, and how warm (or cold) the nights are and how much it rains also matters.

In the future, perhaps due to global warming, beetles and various pests will survive further north and attack tree species they previously had no access to.

If autumn is warmer and spring comes sooner, the question arises whether trees will suffer from these “mutations” of the seasons in the future, since perhaps the growing periods of trees will be longer, with shorter time transitions between warm days. and very cold. A sudden freeze in late fall or early winter can seriously affect the growth of these trees the following spring.

One theory in several articles on fall foliage is that, in the medium to long term, a warming climate will mean that fall colors will no longer be as bright, vibrant, and at their peak. The putative “responsible” factors are dry summers, warm early autumns and periods of heat, as well as heavy rains. It is very difficult to measure how bright the autumn colors are at any given time, and it is quite difficult to convincingly compare how varied the shades of yellow, red or brown are.

Many articles were written in the Anglo-Saxon press trying to explain the differences in autumn colors in different parts of America or Europe. For example, in very popular for “color hunters” areas of Canada, bright red prevails, due to the species of maple, as well as “flashy” yellow due to the presence of a species of “trembling” poplar.

There were also articles that in Europe the color of autumn leaves is yellow and in North America it is red.

Why do we have such beautiful colors in autumn?

How do trees prepare for the cold season? In the spring and summer, they produce a green pigment called chlorophyll, which captures sunlight, giving trees the energy they need to make substances that allow them to grow and develop.

When the temperature drops and the days get shorter, it signals to trees that the growing season is ending, and the trees respond by ceasing chlorophyll production and absorbing nutrients “in the last hundred meters,” creating a sort of winter reserve.

Beneath the chlorophyll produced in the spring and fall are orange, yellow, or red chemicals that appear in the fall after chlorophyll production ceases. In addition to chlorophyll, leaves also contain other pigments, such as carotenoids (responsible for yellow and orange colors) and anthocyanins (responsible for red and purple colors). When the amount of chlorophyll in a leaf decreases, these pigments become more visible.

Thanks to these substances, we enjoy a wonderful colorful landscape at the end of October and the beginning of November.

Different tree species change their leaves at different times in autumn. For example, trees with larger leaves, such as maples, tend to change color earlier in the fall, while trees with smaller leaves, such as oaks, tend to stay green longer.

Data from France show that due to excessive summer heat, trees such as beeches, dogwoods and lindens prematurely changed their leaf color as early as September.

Excessive drought and prolonged heat waves can cause the leaves to dry out and then fall prematurely in late August or early September on some trees, so they do not color.

Because of these changes in the sequence of seasons, the growing season for trees is lengthened, but the transition between warm and very cold days in late autumn is shortened, which means that trees do not have enough time before the first frosts of winter to absorb the nutrients they need.

In mountainous and northern areas, leaves begin to change color earlier than in lowlands or more southerly regions.

Sources: National Geographic, Guardian, BBC, Washington Post, New York Times, Nature Today