why do trees lose their leaves in autumn
Many types of trees shed their leaves as a strategy to survive harsh weather conditions. In temperate forests across the Northern Hemisphere, trees shed their leaves during autumn as cold weather approaches. In tropical and subtropical forests, trees shed their leaves at the onset of the dry season. Trees that lose all of their leaves for part of the year are known as
deciduous trees. Those that donБt are called evergreen trees. Common deciduous trees in the Northern Hemisphere include several species of ash, aspen, beech, birch, cherry, elm, hickory, hornbeam, maple, oak, poplar and willow. In tropical and subtropical regions, deciduous trees include several species of acacia, baobab, roble, ceiba, chaca and guanacaste.
Most deciduous trees have broad leaves that are susceptible to being damaged during cold or dry weather. In contrast, most evergreen trees either live in warm, wet climates or they have weather-resistant needles for leaves. However, there are exceptions in nature, such as that shed their needles every autumn and live oaks that retain their broad leaves for the entire year even in relatively cool climates. Shedding leaves helps trees to conserve water and energy. As unfavorable weather approaches, hormones in the trees trigger the process of abscission whereby the leaves are actively cut-off of the tree by specialized cells.
The word, scindere, which means Бto cut. Б At the start of the abscission process, trees reabsorb valuable nutrients from their leaves and store them for later use in their roots. Chlorophyll, the pigment that gives leaves their green color, is one of the first molecules to be broken down for its nutrients. This is one of the reasons why trees turn red, orange, and gold colors during the fall. At the end of the abscission process, when the leaves have been shed, a protective layer of cells grows over the exposed area.
The shedding of leaves may also come springtime. Without leaves to get in the way, wind-blown pollen can travel longer distances and reach more trees. Bottom line: Many types of trees shed their leaves as a strategy to survive cold or dry weather. Trees that lose all of their leaves for part of the year are known as deciduous trees. Common deciduous trees include several species of maple and oak in the Northern Hemisphere and acacia and baobab in the tropics. Trees actively shed their leaves through a process called abscission. First and foremost, not every type of tree loses its leaves.
Only deciduous trees lose their leaves. There are two important factors related to this process: light and temperature. In many cases, deciduous trees grow in areas that experience cold, harsh winters. Trees drop their leaves to shield themselves during these winter months, because the dry cold winter winds will cause the trees to lose their moisture and the leaves have a large surface area. By shedding their leaves, the trees can preserve the moisture in their branches and trunk, instead of drying out and dying. Also, a tree without leaves is in a state of dormancy and needs less energy to remain alive.
In the spring and summer, leaves photosynthesize the ample sunlight that falls on them. This produces chlorophyll, which causes the green coloring. Photosynthesis generates energy for the tree, and the tree takes in nutrients from the soil to feed its leaves and keep them healthy. The warm and bright colors that the leaves take on in fall have actually been present the whole time, but they have been masked by the chlorophyll. As the days get shorter, the trees receive less sunlight, and therefor produce less chlorophyll. Then they fall off, because the tree does not have the energy to support them through the winter.
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