As humans, we depend on fertile soil to grow our food.  Soil that can grow food in it is called “arable.” Did you know that around 30% of the world’s once arable land can no longer grow food?  The soil can no longer grow food because 60% of it has been washed away into rivers, streams, and lakes. This process is known as “erosion” and it has made bodies of water flood more often and polluted them with pesticides and fertilizers from soil.  Sadly, once the soil is lost in an area, very few plants can grow on the land. It takes hundreds of years for plants to be able to grow on the soil like they used to. Wind and rain are the leading causes of soil erosion. Rainwater speeds up as it falls from the sky and then moves the soil when it hits the ground.  In areas with few plants, soil erosion often occurs because the land is exposed to the full force of the wind and rain without any plants providing a barrier.

The good news is that trees play a vital role in minimizing soil erosion, especially from surface water runoff and flooding.  Trees are able to reduce and stop soil erosion using their root systems. Tree roots have thick stems that branch into finer strands called “filaments.”  These stems and filaments create a network underground that helps to stabilize the soil surrounding the tree and hold it in place. The root system of trees often extends a distance far beyond that of its branches.  Tree roots grow deeper into the soil than small plants and grasses, so they provide a greater defense against erosion.

Tree leaves and branches also play a key role in preventing soil erosion and large landslides.  Leaves and branches fall off of trees to the ground and slow down water flow. When water flows through the land, the water takes more of the leaves and branches that have fallen from the tree than it does the soil.  Tree leaves also stop failing rainwater and reduce the force it hits the ground with. Rainwater flows down the stems of leaves and the trunk of the tree. The rain droplets slow down through this process, and when they hit the soil, the water soaks into the ground.  Furthermore, the leaves and branches of trees act as wind barriers that reduce the force of winds that cause soil to blow away.

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