Which trees turn red in autumn, which turn yellow, and which remain green?

Trees

During the cold winter months, trees and other perennials adapt to harsh conditions. One way to survive is by shedding their leaves. Chlorophyll, which means "green leaf" in Greek, is responsible for the green color of leaves. Participating in photosynthesis, chlorophyll absorbs light energy, undergoes changes as a result of the reaction of carbon dioxide with water to form carbohydrates and oxygen, and then returns to its original state. When sunlight hits the leaves, chlorophyll absorbs almost all colors of the spectrum, except green. The pigment reflects this color. Therefore, humans see only the reflected green of the leaves.

Autumn changes with trees and shrubs

In temperate climates, four seasons alternate constantly. In spring, as the snow melts, roots begin extracting nutrients from the soil, dissolving the accumulated nutrients and distributing them throughout the plant, causing buds to swell and leaves to emerge. But as summer passes, for an unknown reason, the leaves begin to turn red and yellow. This occurs at different times in different tree species, not simultaneously. Others, however, remain green, disappearing beneath the snow without changing color.

Reasons for the changes

The partial breakdown of chlorophyll results in the formation of other pigments responsible for the yellow and orange colors of leaves. The main coloring agent in these pigments is a carotenoid found in the leaf, but chlorophyll masks this color. This is why some trees turn yellow in late summer. The red color of leaves is due to anthocyanin, which is formed only as a result of the breakdown of chlorophyll due to exposure to cold. This explains why some trees turn red in the fall.

The leaf colors are especially vibrant during dry, sunny autumns and temperatures between 0 and 7 degrees Celsius. In rainy weather, leaves tend to be dull yellow-brown and red-brown. Moreover, some scientists argue that the poorer the soil, the redder the leaves will be in autumn, and, conversely, in more fertile soils, yellow predominates in autumn color.

Attention!

Researchers Hamilton and Brown have proposed that plants change the color of their leaves to deter pests from hatching their offspring.

Why do leaves fall from trees, but needles don't?

Autumn leaves, rustling underfoot on a sunny day, are painted in a variety of yellow, orange, and red hues. A tree, deprived of nutrients, is forced to shed what it considers unnecessary. The main reasons for leaf fall are:

dimming the light;
lack of rain;
cold weather;
foliage damage.

As sunlight and air temperature decrease, photosynthesis in plant cells slows, leading to a reduction in the production of sucrose, which is the plant's source of nutrition. To reduce energy expenditure, trees are forced to shed their leaves.

Attention!

It has been established that urban trees shed their leaves later than forest trees, this is due to the presence of artificial lighting.

Lack of rain also triggers leaf fall. Plants, trying to survive, reduce their need for moisture and shed excess material. Coniferous trees are not susceptible to leaf fall in the summer heat because their needles are smaller than their leaves. Trees, sensing the approach of cold weather, accumulate resources for winter survival and shed excess material.

Leaves are damaged not only by insects but also by adverse weather conditions (wind, rain). Furthermore, by the end of the season, harmful substances (metabolites) accumulate in them. It is believed that when a tree sheds its leaves, it cleanses itself. Leaves are attached to the tree by a petiole. As autumn approaches, a layer of cells forms at the junction of the petiole and the branch. These cells grow, blocking the leaf's access to water and nutrients. The connection to the tree weakens. As a result, a gust of wind is enough to tear a leaf from the branch in the fall.

There are several factors that help conifers retain their needles and not shed them annually. These are:

Small area of modified leaves (needles), which helps to retain moisture.
The needles are covered with wax, which helps retain moisture until spring.
The cells of the needles contain components that contain antifreeze substances, thanks to which the trees survive the winter cold.

Coniferous trees also shed their needles, but they do so gradually, and the human eye doesn't notice the change. Pine and spruce completely change their "clothes" within a few years.

When do different trees end their leaf fall?

Deciduous trees begin and end their leaf fall at different times in the fall. Birch, linden, and ash are the first to turn yellow. As soon as chlorophyll begins to break down due to reduced sunlight and heat, yellow and orange colors immediately appear in the leaves. The leaf fall process for these trees begins in early September and lasts about three weeks.

After the first frosts, the leaves begin to turn red and lose their color. maple in autumn, viburnum, and rowan. The subsequent drop in temperature leads to intense leaf shedding by almost all trees. The leaves fall completely in the second half of October. And only in winter oak does not shed its yellow-brown leaves and stands all winter with dried foliage.

Attention!

Birch trees shed up to 30 kg of leaves, and maple trees shed about 50 kg.

Evergreen trees and shrubs

Evergreens include all conifers, with the exception of larch, which sheds its leaves (needles). In the wild, it grows primarily in areas with cold winters. However, further south, deciduous trees and shrubs are found that remain green in autumn. These include:

Honeysuckle is an evergreen plant and is a bindweed;
Heather is a low shrub that is widely used in creating garden compositions;
Bay laurel is a low tree with thick, shiny leaves used in cooking.

Leaf fall is a natural biological process that occurs in nature every year, helping trees survive difficult weather conditions so that they can be reborn again in the spring.