On flat land, properly managing the landscape and incorporating agroforestry techniques such as alley cropping and windbreaks leads to a more stable and fertile soil. On sloped land (an incline exceeding 5%), things become more complicated with greater soil erosion which is detrimental to the stability and fertility of the soil. During rains, runoff will flow down the hillside and carry away topsoil along with all of its nutrients. Contour planting can help mitigate this. When developing contours with trees or other plants, the trees are planted closely together along measured contour lines, using the assistance of a tool called an A-frame. The plants bind the soil, forming a small ridge or dam. When water reaches this ridge, it slows or stops flowing, forming a puddle, and has more chance to percolate into the soil. The land levels out behind the contour, creating terraces.