This is where water taken up from the roots moves through the plant to be utilized for photosynthesis in the leaves. Water availability has a direct impact on the health of forests and their inhabitants, which shows the importance of the relationship between forests and water. Trees are made up of more than 50 percent water and need a steady source of it in order to grow and stay healthy. Three of these processes are cycles – the water cycle, the nitrogen cycle and the carbon cycle. Plants are important in several key processes involved in the interacting systems of the Earth, including the hydrosphere, atmosphere and biosphere. Trees, like people, need to “drink” a lot of water. Trees also prevent erosion. As the National Oceanic and Atmospheric Administration points out, the water cycle is often taught as a simple circular cycle of evaporation, condensation and precipitation. Note: This section of the Water Science School discusses the Earth's "natural" water cycle without human interference. As trees are larger than other plants, their contribution is significant. Trees, like most plants, undergo a process called evapotranspiration. Forest trees play a major role in influencing the flow of water resources. The water is then released from the leaves into the air as water vapor. Plants play a key role in maintaining the balance of each of these cycles. It makes it harder for the water because it clumps the soil together and makes it hard for the water to pass through as well as the roots absorb the water that in other cases would erode the soil. ... An acre of corn gives off about 3,000-4,000 gallons (11,400-15,100 liters) of water each day, and a large oak tree can transpire 40,000 gallons (151,000 liters) per year. Forests and trees play a major role on water cycles and cooler temperatures, contributing to food security and climate change adaptation. Atmospheric factors affecting transpiration. But trees are more than just water users; they are an integral part of the water cycle. Planting trees would affect the water cycle because it would increase transpiration. Because of their enormous roots the trees help hold together soil making it harder for the water to erode the soil.