Trees remove large quantities of nutrients from the soil each year utilizing them for growth and development. In a forest setting, trees have a natural nutrient cycle in which the nutrients they remove from the soil are returned when leaves, twigs and fruit fall to the ground and decompose. This natural cycle is self-sustaining and has allowed forest trees to grow large and healthy for centuries.
In our urban environments, the natural nutrient cycle is broken, as the organic forest floor has typically been replaced by turf grass. Falling leaves, twigs, and fruit are quickly removed to maintain a manicured lawn. Competition with lawns and other underlying plants further depletes the nutrients from our soils. If this weren’t enough, urban tree roots are confined by smaller spaces. Roads, driveways, patios, and houses all limit the area urban trees are able to obtain nutrients from. Urban trees end up being less healthy and live much shorter lives than those in the forest. They are lacking essential nutrients they need to grow due to poor soils, abiotic problems (man-made causes), bad weather, etc. If they had a forest floor and ecosystem nutrition available to them, fertilization would not be needed.