Outforia Quicktake: Key Takeaways
- Leaves change color in the fall due to a complex chemical process in deciduous trees, influenced by the length of daylight hours and weather conditions.
- Deciduous trees produce and conserve energy through photosynthesis in spring and summer, but start to break down chlorophyll in fall, revealing new colors in the leaves.
- Three main pigments involved in autumn leaf colors are chlorophyll, carotenoids, and anthocyanins.
- Leaves eventually fall off as trees undergo a process called abscission, protecting them from harsh winter conditions and conserving energy.
- Some trees that change color in the fall include maple, oak, hickory, and aspen trees, while evergreen trees like pines, spruces, firs, and cedars keep their color year-round.
Every year, the Earth paints landscapes with beautiful fall foliage. Green leaves turn to hues of orange, red, yellow, and tan. But you might be wondering, why do leaves change color in the fall? What’s the science behind it?
Trees work throughout the spring and summer to produce and conserve energy in a process called photosynthesis. As fall and winter approaches, the weather changes and days become shorter. The leaves of deciduous trees begin to break down the chlorophyll that’s used to absorb energy from the sun. As a result, the leaves reveal new colors.
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Why Do Leaves Change Color in the Fall?
Trees undergo a complex chemical process that causes their leaves to change color. Deciduous trees are the types of trees that change color. Evergreen trees, as the name suggests, stay green year-round.
Just like most plants, trees participate in the process of photosynthesis to create energy and food. The reason trees and other plants are green is due to a substance called chlorophyll. It has a green pigment, which is why leaves are green in the spring and summer.
Scientists haven’t completely unraveled all the intricate details of why leaves change color in the fall. However, there are a few things that we do know about the seasonal cycles of trees and leaves.
Length of Day
The biggest influence on leaf color change is the length of day.
Daylight hours become shorter in the fall. Autumn acts as a transitional period between summer and spring.
There’s still enough warmth and direct sunlight during the fall for deciduous trees to maintain their leaves. As night becomes longer, trees get less sunlight. The sunlight they do get isn’t as direct as it is in late spring and summer. This prevents trees from producing as much energy as they would in the warmer months.
Trees recognize the change in sunlight and start to conserve the energy that’s been absorbed through the spring and summer. New leaf pigments are revealed or created in this process.
The veins in leaves hold fluids for trees. In the fall, trees begin to cut off this fluid supply from the leaves. Sugars trapped inside the veins of leaves produce new pigments. There are also pigments that already exist in the leaves that are covered by chlorophyll until fall.
Weather also plays a role in autumn colors. These changes are less consistent as weather patterns can vary year to year.
The biggest influence weather has on fall color changes is the brilliance of the leaf pigments.
During the growing season, warm and sunny days with cool nights allow trees to get lots of energy. Cool nights allow trees to gradually close off the veins in the leaves, rather than more abruptly. These conditions help trees produce more sugar which creates more vibrant colors.
If there’s a drought in the late spring or summer, this can cause leaf color changes to be delayed by a few weeks. Warmer than normal temperatures in the early fall may prevent some trees from producing brilliant colors.
Ideal conditions for the best fall colors include a warm and wet spring followed by sunny summer days with occasional rainfall.
What is Photosynthesis?
Before we jump into the specifics of fall colors, let’s review the process of photosynthesis.
The leaves of trees absorb carbon dioxide and water. Trees need sunlight to convert these chemical compounds into sugars, which provide the tree with fuel. Within this process, trees release oxygen into the environment, which helps keep the air clean and healthy!
Tree roots suck up water from moisture in the soil. The water is carried through cells called xylem. The cells transport the water up to the leaves. Trees absorb energy from sunlight and carbon dioxide from air.
Once a tree creates sugars from water, sunlight, and carbon dioxide, its leaves produce sugar. Phloem cells help transport the sugar back into the tree. The sugar is stored in the trunks and roots of trees in the form of a starch. Trees will also use the sugars immediately to grow.
Autumn Leaf Colors and Pigments
Pigments are the reason trees, fruits, and other plants have color. There are different types of pigments that produce various colors. For example, orange carrots have a pigment called carotene, which is why they’re orange.
There are three leaf pigments that appear in autumn leaf colors:
- Chlorophyll – The most common pigment that causes leaves to appear green in the spring and summer. Evergreens hold onto their chlorophyll pigment year-round.
- Carotenoids – Yellow, orange, and red pigments produced chemically by photosynthetic plants, algae, and bacteria.
- Anthocyanins – Water-soluble pigment that produces red, blue, and purple colors.
Chlorophyll and carotenoids are always present in leaves. As trees undergo their seasonal fall color change, carotenoid pigments are revealed.
Anthocyanin pigments are produced as a result of seasonal change. Anthocyanins aren’t a part of the growing season. These pigments are produced by leaves when sugars in leaf cells build up.
Fruits, vegetables, and flowers have some of these same pigments. As mentioned before, carrots have carotenoids. This pigment is also present in bananas, corn, and daffodils. Cranberries, red apples, and concord grapes have anthocyanins.
Why Do Leaves Fall?
When chlorophyll is continuously produced by trees in the spring and summer, the leaves remain green. In the fall, trees begin a process called abscission.
When trees begin abscission, chlorophyll production slows down and trees start to cut off their leaves. Once chlorophyll production is halted, the chlorophyll begins to break down.
Deciduous trees create a protective seal between the leaves and branches, which cuts off any nutrients that the leaves or trees may transport to or from each other. Once the seal has been formed, leaves begin to brown and fall off.
Although trees might look sad and bare in the winter, losing leaves is an important process trees must go through to ensure winter survival.
If a deciduous tree didn’t lose its leaves, it would risk dying in the winter. Harsh, cold temperatures can damage leaves.
Trees have special light receptors called phytochrome and cryptochrome. These light detectors allow trees to notice changes in the length of the day and night.
So when a tree notices nights are becoming longer, they begin their complex winter survival process of leaf-color change and dormancy.
How Do Dead Leaves Help Trees?
Once leaves turn brown and fall off trees, their job doesn’t stop there. Dead leaves will fall below to the ground and begin to decompose.
Leaves continue to provide nutrients to trees in the decomposition process. They provide the soil with nutrients and turn into a spongy layer, which holds more moisture at the base of trees. This allows trees to get the moisture they need, even when there isn’t a lot of precipitation.
Decomposing leaves are also important for providing habitat and food to critters that live in the soil.
Types of Trees That Change Color in the Fall
Not all trees have the ability to change colors in the fall. Colors and time of change can also differ between a particular genus or species. Here is a list of some deciduous trees that boast vibrant fall colors:
Maple trees are known to exhibit brilliant fall colors. In some parts of the world, such as southern Asia and the Mediterranean, maples can stay evergreen.
Autumn maple colors can vary depending on the species. Red maples are known to have a fiery scarlet color. Sugar maples turn reddish-orange. Black maples can be bright yellow to yellow-orange. Striped maples may be a dull yellow or not boast any bright hues.
Red maples can be found in deciduous forests in the eastern half of the US. Sugar maples are native to hardwood forests in the northeastern and midwestern US.
Black maples are concentrated throughout the north central US. Striped maples are most abundant in the northeastern US.
All oak trees are likely to produce red, brown, or russet pigments in the fall. Oak trees can be found in temperate to tropical climates, depending on the species. North America hosts the largest number of oak tree species.
Live oak trees are exclusive to the southern US. Live oaks differ from other oak and deciduous trees because they replace their leaves at different times of the year, rather than just in winter.
Some oak trees are evergreen and keep their green leaves year-round. However, many oak species turn a beautiful glowing bronze or reddish-orange.
There are at least 17 hickory tree species found around the world. Some hickories are native to China and India, while others are native to Canada, Mexico, and the US.
Hickories are found in temperate climates. They belong to the walnut family Juglandaceae. More than 10 hickory tree species can be found in the central hardwood forests of the US.
Hickory trees are known for producing vibrant yellow and golden orange colors in the fall.
The eastern US is dominated by color-changing trees that thrive in the temperate eastern deciduous forests. However, the West also has some vibrantly-colored trees in the fall. Aspen forests are found throughout the western US.
These tall, skinny trees have a beautiful white bark decorated with dark markings. In the fall, aspen leaves turn bright yellow which compliments their light bark color. Peak color times vary depending on location.
Aspen trees begin changing colors in mid to late-September in areas farther north, such as Fort Collins, Colorado. Colors change in late September to early October as you travel farther south.
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Types of Trees That Stay Green
As the name suggests, evergreen trees stay green all year. However, there are some evergreen trees that lose their needles in the winter.
Conifers have different types of leaves than broadleaf trees. Conifers have needle or scale-like leaves.
Evergreen trees have a special wax coating that protects the leaves from freezing temperatures. This allows the trees to maintain the chlorophyll pigments year-round. The leaves of evergreens eventually fall when they’re at the end of their lifespan.
Examples of conifers that stay green year-round include:
Larches are one example of an exception to evergreen conifer trees. Larches are deciduous conifers that don’t stay green year-round. Instead, they turn bright yellow in the fall and then lose their leaves by winter.
Conifers are considered ancient trees because a number of close conifer relatives have been around for hundreds of millions of years.
Conifers are able to stay green year-round because they continue to photosynthesize in the winter. These trees rely on the storage of mineral nutrients and water in the needles to keep them green.
What is the Best Time of Year to See Fall Colors?
The best time of year to see fall colors can depend on where you live. Color-changing trees will begin the chlorophyll break-down process earlier in the North than those in the South.
Peak fall color times for northern states like New England begin in mid to late-September. Leaf-color changing times can also depend on the weather conditions the area had in months prior.
As you travel farther south to states like Virginia and North Carolina, colors are most vibrant in early to mid-October. Southern Virginia and North Carolina boast fall colors in late October.
Southernmost states like Florida don’t have as many color-changing trees as northeastern states. But deciduous trees in this region typically change colors in late fall and early winter since it’s warmer.
Deciduous trees at higher elevations found in the West change colors earlier. According to the Colorado State Forest Service, the best time to see aspen fall colors is in September and early October.
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Best Places to See Fall Colors
Many people travel far and wide to see leaf color changes in the eastern US. This activity is referred to as “leaf peeping”.
Skyline Drive is a popular scenic route to take in all the fall colors. The winding road is lined with vibrantly-colored trees in the fall.
Skyline Drive is located in the Blue Ridge Mountains of Virginia and connects to the Blue Ridge Parkway. The Blue Ridge Parkway travels through the Great Smoky Mountains of North Carolina.
Some northeastern states that are known for amazing fall colors include:
- New Hampshire
- New York
Although deciduous forests are most abundant in the eastern half of the US, there’s also many locations in the West to do some leaf peeping!
Common hotspots to see leaf color changes in the Midwest and West include:
- Great Smoky Mountains National Park, Tennessee
- Superior National Forest, Minnesota
- Aspen, Colorado
- Ozark Mountains, Montana
Alaska has the earliest start to leaf color changes compared to other states. If you find yourself in Alaska in late August to early October, you might catch some beautifully-colored fall foliage. The Chugach National Forest boasts yellows and oranges from aspen, birch, and cottonwood trees.
Fall colors in the deciduous forests of Asia are similar to those in the US. In Europe, many deciduous tree leaves change to golden yellow and orange.
Some popular places to visit in the fall in other parts of the world include:
- Kyoto, Japan
- Nami Island, South Korea
- Burg Eltz, Germany
- Hallstatt, Austria
- Lillafüred, Hungary
- Lauterbrunnen, Switzerland
Of course, there are many other places around the world that have a colorful autumn season. The key is to find the deciduous forests and the right time of the year.
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Why do leaves change color in the fall FAQ
What happens to photosynthesis in the fall?
Trees spend spring and summer photosynthesizing to create food. Once fall approaches, there’s not as much direct sunlight and temperatures cool.
Most deciduous trees become dormant after losing their leaves. This allows them to conserve energy they’ve stored up in the warmer months.
Once temperatures begin to warm up again, they begin to soak up more direct sunlight and produce leaves again.
Where do leaves change color first?
Leaves change color first in northernmost areas with deciduous trees. Temperatures begin to cool earlier in the year in the North.
As you travel farther south, it changes gradually to mid and late fall. Southernmost deciduous forests experience the latest color change, typically in late fall to early winter.
Do leaves change color everywhere?
Leaves don’t change color everywhere because some places don’t have temperate deciduous forests. These forests are most abundant in eastern North America, western and central Europe, and northeast Asia.
Areas dominated by conifer forests don’t experience the same color change that deciduous forests do.
What temperature makes leaves change color?
Temperature doesn’t play a huge role in leaf color change. It’s the length of the day. Trees can still absorb the energy they need when they have sunlight.
The combination of less direct sunlight during the day and longer nights is the primary cause of leaf color change. It just so happens that temperatures are mixed into all of this, since it gets colder due to lack of direct sunlight.
Is leaves changing color a chemical or physical process?
Leaves changing color is a chemical process because chemical reactions occur. The process involves chemical compounds like carbon dioxide and water.
Although the process of leaf color changes may appear physical to the human eye, there’s a lot of chemical changes going on inside trees and their leaves.