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Trees play an important role in the life of our planet, contributing three essential elements: air, water and fertile soil.
Air
Photosynthesis is the process by which green plants use energy from the sun to drive a series of chemical reactions leading to the formation of carbohydrates. These carbohydrates in turn provide energy for the animals that eat the leaves or bark of the tree.
For photosynthesis to occur, the plant must have a supply of chlorophyll, carbon dioxide and water. Chlorophyll is found in all green plants. Carbon dioxide comes from atmosphere, while hydrogen and oxygen come from water in the soil. Plants return oxygen to the air as a waste product, providing the oxygen that humans require in order to breathe. This is why it said that trees are the "lungs" of the planet.
Water
Trees play several roles in the water cycle. Tree roots help to secure the soil, allowing it to absorb rain water. Plants can then use the stored water for future use. Soil erosion happens when there are no roots to anchor the soil. In rainforests, the large leaves provide the soil with protection from the sun's harsh rays and torrential rains. Without the leaves, the soil would wash away. Trees also act as windbreaks and decrease evaporation of moisture from the soil.
Trees assist the water cycle in another way, by recycling the moisture that falls as rain through a process called transpiration. In this process, plants take up water through their roots and release it into the air through their leaves. This keeps the leaves cool and helps the tree absorb nutrients from the soil. The moisture released from the leaves will form clouds that later return the water to the Earth as rain.
Soil
Trees also help to form and conserve the soil. They help to determine the amount of light, heat and moisture that reaches the soil, and they help protect against erosion. Trees also supply raw material as they decompose or die, adding important nutrients to the soil.
Trees and plants also depend on soil for life. Soil is created by living and non-living elements of the environment. It is influenced by six factors: climate; geology; underlying rocks; topography (i.e., if the land slopes or is near a river); the action of living things, including humans; and time.
The six components of soil (all of which affect fertility of soil) are mineral particles (silt, clay and sand); humus (organic material that forms a thin film around each soil particle); nutrient ions (calcium, nitrogen, potassium); water; air between soil particles; and living organisms such as worms and microscopic life. The three main layers of soil are topsoil, subsoil, and the partially broken-down rock that is in the process of becoming subsoil.
New soil is continuously being made, but soil is eroded almost twice as fast. Erosion is often the result of human action, such as cutting down trees in the rainforest or poor agricultural practices.
Soil acts as a natural sponge, absorbing water and releasing it slowly. But if soil is unstable, it cannot do its job. For example, in the Himalayas, the vast mountain system of central Asia, much of the forest that used to hold the soil in place on the mountain sides has been cut down. The result is that once-fertile soil is washed away by the rain. When hard rains arrive, the water rushes down the mountain slopes and into rivers, causing flooding in lowland towns and villages. Floods cause damage to communities, resulting in loss of housing, infrastructure and sometimes death.
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