Trees and lawns both require sunlight, water, nutrients, and rooting space to maintain vigor and and live up to their genetic potential. In the landscape, every plant competes with their neighbors for these resources. 

Given their different requirements and the close proximity of tree and lawn roots, the treatment of one may negatively impact the other. Herbicides used in lawn care may cause severe damage to trees when misapplied. Fertilizer applied to one plant will also be absorbed by the roots of a nearby plant. This can be a good thing if done intentionally, but excessive fertilization of either trees or turf can result in excessive aboveground growth or reduced disease and pest resistance.