Skip to main content

How do trees detect seasonal changes?

When temperatures get warm and the sun beams down, humans and animals usually seek refuge in the shade — or air conditioning! The same can’t be said for plants, though. Plants, like trees, don’t leave their roots while alive, so they must be able to cope with fluctuations in temperature throughout the year. The natural environment can be a harsh place, so how do trees survive in it? How do they know how and when to adjust to their surroundings?

Large oak tree with orange leaves in autumn
Holger Graebner / Shutterstock

Why do some trees lose their leaves?

The act of trees losing their leaves isn’t too unlike some activities that happen within your body! Similar to humans, plants have hormones. In plants, chemical messengers are often referred to as phytohormones. Phytohormones regulate different metabolic processes in plants, such as the formation of fruits. One class of phytohormones called auxins are essential to proper development throughout the plant life cycle.

Recommended Videos

Particularly important for growth, auxins are partially responsible for trees dropping their leaves. Ethylene, another phytohormone, also contributes to seasonal changes. The scientific term for shedding by an organism is abscission.

Auxin levels are influenced by environmental conditions. As winter or the dry season approaches, less auxin reaches a plant’s leaves. This causes fewer nutrients to reach the leaves, eventually leading to them dying and falling off the tree. Plants keep track of changes in light, temperatures, precipitation, or a combination of those factors in order to know when to stop supplying their leaves with nutrition. The evolutionary advantage to abscission is that it allows a plant to better ration out what limited food it will get during the winter/dry season.

How do plants detect changes in the environment?

Many plants have cells known as photoreceptors, which detect light. There are a number of types of photoreceptors — some detect blue light, others the amount of light exposure a plant gets. All photoreceptors work together to sense when the season is shifting. Akin to how we smell and see, a plant detects light.

Regarding temperature changes, the various enzymes in a plant (like phytohormones) can only work within particular temperature ranges. Because enzymes are critical to a plant’s metabolism, without them some metabolic processes can’t occur. Plants detect temperatures of both the soil and the air surrounding them. And though an enzyme may be inactivate in the cold, sometimes a cold period is necessary in order for a plant to bloom in the spring.

Why don’t all trees lose their leaves?

Actually, even evergreen trees lose their leaves! Instead of shedding seasonally, evergreen trees are constantly undergoing abscission. Evergreen trees lose their leaves gradually in smaller quantities than non-evergreen trees. Trees that change with the seasons are called deciduous trees.

When you think of an example of an evergreen tree, you probably think of pines or other coniferous trees. But evergreen plants exist outside of cold environments, too. Tropical rainforests have primarily evergreen plants, for example. Eucalyptus trees are another type of evergreen. Something a majority of evergreens have in common is that they grow best in environments where the temperature and rainfall are relatively stable throughout the year.

How do trees know when to bloom?

Enzymes come into play again here! Most plants have an ideal, small range of temperatures that they grow best in. The hypothesized molecule that probably causes flowering in plants is the florigen. Like other phytochromes and enzymes in general, the production of florigen is triggered by certain temperature and light conditions. Moreover, florigen is not produced on the same day in all parts of a plant in order to maximize the flowers’ potential to thrive.

Florigen is only produced at certain, predictable places in a particular plant, meaning you’ll always know where a plant will bloom. One gene known to be involved in florigen localization is APETALA1. Research is still ongoing regarding the molecular basis behind the growth and seasonal cycles of plants.

Red leaves on a tree branch
Image used with permission by copyright holder

Autumn is a spectacular season, with its hues of red, yellow, orange, and brown, fallen leaves, and cooling temperatures. Abscission is just one of the many plant processes influenced by environmental conditions. Plants are very complex, although they might look simple.

Dragon fruit plant care: How to grow this tropical beauty
Grow fresh dragon fruit at home
Ripe dragon fruit

Growing your own fresh fruit is a fun way to increase the amount of tasty, healthy snacks in your home. There are tons of delicious fruits you can grow, from classic blueberries to the more unusual strawberry tree. Dragon fruit is one fruit you might not have considered growing at home. These unique-looking tropical fruits are delightful, but are they easy to grow? They’re tricky, but not impossible! If you want a steady supply of fresh dragon fruit, here’s everything you need to know about planting and caring for dragon fruit plants.
Planting dragon fruit plants

The best time to start planting dragon fruit plants is in early to mid-spring. While you can plant them later, they won’t have as much time to grow during the year. If you plan on starting with seeds or a small sapling, you can start your dragon fruit plants indoors during the winter and transplant them in the spring to speed things up.

Read more
Beautyberry care made easy: Your complete guide to growing this shrub
Growing your own beautyberry tree
American beautyberry shrub

There are several reasons you might want to add a shrub to your garden. They can have gorgeous flowers, they keep your garden from looking bare during winter, they create a small privacy hedge, and they even benefit your local wildlife. While fruit may not be at the top of your list of reasons, we have a shrub that might change your mind on that! Beautyberry shrubs, true to their name, have incredibly beautiful berries. Want to grow your own? Here’s what you need to know about growing a beautyberry shrub and how to care for your beautyberry in winter.
What are beautyberry shrubs?

Beautyberry shrubs are a group of shrubs in the Callicarpa genus with a fairly wide native range. There are species native to North America, South America, Australia, and most of Asia. There are both evergreen and deciduous varieties, and the berries are technically edible (although the raw berries have an unpleasant flavor). Callicarpa americana, the American beautyberry, is found primarily in the southeastern U.S. It’s a deciduous species, and the berries are sometimes used to make a jam that is much tastier than the raw berries.

Read more
How to grow wintercreeper, gorgeous green and gold foliage
Your guide to growing these evergreen vines
Green and yellow wintercreeper leaves

If your winter landscape is looking a bit empty, you might be on the hunt for some beautiful evergreen plants to fill the space. There are many gorgeous evergreen plants to choose from, including trees like various types of pine and smaller shrubs such as holly. One plant you may have heard of is wintercreeper. If you’re not familiar with this plant and are wondering what it is and how to grow it, then you’re in the right place. This guide to wintercreeper care will answer all your questions about growing wintercreeper indoors and out.
What is wintercreeper?

Wintercreeper, also called fortune’s spindle or Euonymus fortunei, is an elegant evergreen vine with solid green or variegated green and white or yellow foliage. It grows quickly and can be trained to grow over a trellis, up a wall, or as a ground cover. This creates a beautiful display of densely growing vines and leaves, which is great for filling space. As a groundcover, it requires less maintenance than grass lawns, and the durability of the vines is a highlight for many gardeners.

Read more