The Science Behind Fall Foliage

By Dylan Stuntz, American Forests

It’s officially been fall for a little more than a week, and for anyone who lives near a deciduous tree — one that sheds its leaves in the fall — this means some beautiful sights are about to occur. But why do trees go through these changes? There’s a complex chemical process that goes on inside every deciduous tree, and maybe understanding it can give you even more appreciation for such a stunning sight.

To understand why leaves are the color they are, you first need to become familiar with the inside of a leaf. Leaves get their green color from a chemical called chlorophyll, which helps the tree take in sunlight. The tree uses the sunlight in a process called photosynthesis, which is how the tree eats, so to speak. It uses the sunlight to break down carbon dioxide (CO2) and water (H20) it absorbs, turning the CO2 and H20 into oxygen, which gets expelled, and glucose, which the tree consumes for energy.

If you imagine a tree as a factory, then the leaves are seasonal workers. They do their job when resources are coming into the factory (sunlight, water, carbon dioxide), but when resources stop coming in, there’s not much for the workers to do, so the tree sends them a pink slip. Leaves require energy from the tree, so like any good factory, the tree engages in a cost-benefit analysis. When the days become shorter, the tree no longer wants to waste energy on leaves. This starts the internal chemical process that creates fall foliage.

The change in leaf coloration is dependent on the amount of sunlight that the tree takes in. As the seasons change, the days get shorter and the night get longer. Eventually, when the nights reach a certain length, chemical processes in the tree will start to block off the connection between the tree and the individual leaves, by creating a corky layer of cells known as the abscission layer. This layer is to protect the branch when it inevitably becomes exposed to the open air, once the leaf has fallen. The abscission layer protects the tree, but it also disrupts the flow of nutrients and chemicals that move from the branch to the leaf and back. Chlorophyll breaks down when exposed to sunlight, so as a result it needs to be constantly replaced. The abscission layer interrupts this renewal process, so as a result once the chlorophyll starts to fade, other colors start to emerge.

Two chemicals are responsible for the fall coloration of leaves. Carotenoids create orange and yellow pigments, and anthocyanins create shades of red and purple. The carotenoids are present in the leaf all summer long, but they’re masked by the green of the chlorophyll. As soon as the chlorophyll renewal is halted, the green begins to fade and the vibrant fall colors appear. The second chemical, anthocyanin, forms as a result of the glucose formed by the remaining, faded chlorophyll. The glucose then becomes trapped in the leaf by the abscission layer, resulting in the formation of anthocyanin.

The colors of a particular tree are a result of the carotenoids and the anthocyanins reacting to each other in different amounts, in combination with any chlorophyll left. The formation of these chemicals and the amount of each of them are dependent on temperature, moisture and sunlight, so every foliage season is unique, because every season the chemical balance found inside the leaf changes.

The anthocyanin formed in the right-hand part of this leaf because it was exposed to sunlight, but the left side was probably in shade, so the carotenoids caused it to stay yellow.

Carotenoids and anthocyanins also break down after being exposed to sunlight. If a leaf manages to stay on the branch after the chemical processes have broken down, you would see the bright colors fade until it would finally be brown, a result of a final chemical, tannin. Tannins are found in the membranes of the cells that make up the leaves, so they never fade, which is why brown is the final color present in late autumn.

In these leaves, the tannins are interacting with the carotenoids and anthocyanins to create subtle, stunning combinations.

So when you go to snap a picture of copper-colored leaves for your Instagram, take a minute to appreciate the intricate chemical interactions going on!

The post The Science Behind Fall Foliage appeared first on American Forests.

Unforced variations: Oct 2017

This month’s open thread. Carbon budgets, Arctic sea ice minimum, methane emissions, hurricanes, volcanic impacts on climate… Please try and stick to these or similar topics.

Forest Digest: Week of September 25, 2017

October 1st, 2017|Tags: , , , , , |0 Comments

Find out the latest in forest news!

World’s Longest-Living Trees Crowded Out by Climate Change – VOA News

Bristlecone pines can live up to 5,000 years, but researchers are worried about climate change’s effect on these old giants. Scientists at the University of California, Davis, found that a similar tree species, the limber pine is taking key spots on mountainsides where the bristlecone pine would normally grow. Limber pine normally grows at lower elevations, but rising temperatures have encouraged it to move up to take over bristlecone pine habitats.

One of the world’s most popular trees arose near the Arctic CircleScience Magazine

DNA analysis by the Morton Arboretum in Lisle, Ill., has found that the common ancestor for North American oaks originated much farther north than previously thought. Most botanists had hypothesized that oak trees developed in the tropics, and then spread northward, but after looking at over 10,000 pieces of DNA from over 300 species of oak, researchers found that the ancestor for modern oaks arose 45 million years ago in what is now northern Canada.

Funding Trees for Health — Global Solutions (The Nature Conservancy)

A study by The Nature Conservancy has found that planting urban trees is one of the most cost-effective solutions to increasing the health and life expectancy for urban residents. The study looks at critical health outcomes and identifies major barriers to be overcome to allow cities to realize the potential urban forestry.

Funding Trees for Health — PBS EONS

The coal we burn today is called a fossil fuel, but what fossils did it come from? Three hundred million years ago, it was a plant known as a “scale tree,” a seedless tree living during the Carboniferous period. At its peak, this tree made up over half of the biomass in North America and Europe. The species died out about 272 million years ago, but millions of years of exposure to heat and pressure gradually turned all that biomass into coal.

Dead mangroves shut down carbon cycleCosmos Magazine

Mangroves are effective at fighting climate change, but it’s been found that mangrove dieback can actually contribute to climate change. That’s the result of a study done by Southern Cross University in Melbourne, after studying a massive dieback of mangroves that occurred in 2015. Researchers found a variety of factors contributed to the mangrove dieback, low rainfall, high temperatures and low sea levels as a result of El Niño.

Brazil Backs Off Controversial Plan to Open Amazon Forest to Mining — EcoWatch

The Brazilian government has publicized that it will no longer move forward on a plan to allow mining in a protected Amazon reserve. The reserve is larger than Switzerland and believed to hold large deposits of gold, manganese, iron and copper. Brazil’s president announced the decree to open up mining last month. A few days after it was announced, the courts suspended the decree, and on Sept. 25 the Ministry of Mines and Energy (MME) announced it would not move forward on the president’s decree. However, the MME did put out a statement indicating that they would be receptive to other proposals in the future, saying “the country needs to grow and generate jobs, attract investment to the mining sector and even tap the economic potential of the region.”

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The Tunes of Trees

September 28th, 2017|Tags: , |0 Comments

By Dylan Stuntz, American Forests

Headphones are so ubiquitous today, it’s common to see people walking by with earbuds in, going about their days listening to their favorite music or the latest podcast. If you fall into that camp, consider disconnecting the next time you venture outside, because there are a variety of mental, physical and social benefits to just listening to the sounds of the natural world.


Researchers recently conducted a study in which participants listened to silence, Mozart and nature sounds, while recording self-reported stress levels, pulse rate and muscle tension. They found that after just seven minutes of nature sounds, participants reported lower stress levels along with a measurable decrease in muscle tension and pulse rate. Surely you can find seven minute out of your day!

Rather than spend seven minutes on “Hey Jude”, next time consider listening to a different type of beetle.

Another study was conducted measuring self-reported stress and physical stress symptoms after doing difficult arithmetic problems, and found similar results. Participants listening to nature calmed down quicker than those listening to a variety of other sounds. The next time you find yourself stymied by a difficult problem? Go take a walk in a natural setting and let the sounds wash over you — it may help you calm down both mentally and physically.


In a similar vein, scientists at Brighton and Sussex Medical School measured brain activity while listening to nature sounds, and they found an increase in brain activity associated with attention span. A different study found that birdsong was reported as the most effective sound to restore attention. It’s been found that nature sounds can help reduce time needed to recover from “attention fatigue,” which refers to the mental exhaustion that happens when you’ve been focused on one task for too long. If you’re feeling overwhelmed, exhausted or just simply unable to focus, a bit of time in nature can work wonders.


No one rocks quite like this robin!

Other than the health benefits, there’s also the untold benefit of simply being present in nature and aware of all the life around you. There’s a subtle piece of music being conducted every day, and you can hear it with the wind in the trees, the babbling of a brook or the melody of a songbird. To be outside and hear such a unique symphony, which only exits in that specific moment in time, there’s something magical about that. Your playlist won’t go anywhere, but to just take a walk in the woods and truly listen, that’s a playlist that can never be found anywhere else.

There’s music found outside that calms you down, makes you more attentive and plays 24/7. It doesn’t require a subscription, won’t deplete your phone battery and can be found almost anywhere. All you need to do is listen.

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Digital Marketing Intern

The Digital Marketing Intern’s main responsibilities will be to assist with research, content and scheduling for American Forests’ social media channels, as well as content development and management for our website.

The Communications Department is also responsible for all publicity activities related to the organization, as well as creating marketing materials, such as brochures, online videos and print and web PSAs. Interns in this department will have the opportunity to assist on projects related to all of these items.

Job Description

  • Perform daily report of top content.
  • Assist in developing content calendars, drafting and scheduling posts.
  • Support analytics tasks, including competitor and industry research.
  • Conduct photo research for use on platforms; edit images for various platforms.
  • Perform internal platform audits and make suggestions for content.
  • Assist with strategy and planning of web projects.
  • Support content development through web copy.
  • Analyze website and contribute suggestions for structure, content, strategy, etc.
  • Support other Marketing and Communications projects as needed.



Candidates must be currently attending an accredited four-year college or university, preferably enrolled in a communications/public relations, journalism, marketing or English program. American Forests internships are unpaid and available year-round to students receiving academic credit. While unpaid, American Forests’ internships are an opportunity to receive academic credit while gaining experience in the nonprofit environment, knowledge of conservation issues and programs, and by serving a key role in the organization’s communications strategy.


  • Strong writing, grammar and editing skills
  • Experience with developing content for social media required
  • Familiarity with various content management and analytics systems, esp. Hootsuite and WordPress
  • Knowledge or proficiency in Adobe Creative Suite or similar design skills a plus
  • Basic HTML skills a plus
  • Interest in working for a nonprofit
  • Independent worker
  • Organized, deadline-oriented and creative


To Apply

We are currently accepting applicants for the fall 2017 and spring 2018 terms. To apply for this internship, please send a cover letter, résumé and two examples of social media/marketing work to Emily Barber, Marketing Manager, at The position will remain open until filled.

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