Why Is it Hard for Plants to Grow on Steep Hills?

Weather Factors

• Plants need a stable environment to live out their lives from germination to maturity. Erosion, or the wearing away of the earth's surface, removes the top and most fertile layers of soil, making it difficult for plants to grow there. The top layers are composed of decaying vegetation that supplies plants with all the nutrients they need, and they also absorb the water that is crucial to plants' survival. Water movement is affected by the earth's gravitational pull and always seeks a lower spot. On flat surfaces, the soil absorbs rain water and melting snow and stays put, but on slopes, it flows freely, taking the soil along with it.

Effects

• As water carries the soil down a hillside during, or shortly after, a storm, seeds that have been deposited there by nature or by humans don't have enough time to germinate and take hold, and any plants growing there run the risk of being uprooted and washed away. Soil is also often stripped from the roots of larger established plants, weakening their hold on the terrain. Plants not washed away suffer as a result of no longer having enough soil to sustain them and they eventually die.

Considerations

• Erosion can happen swiftly, as in the case of an intense storm that drops great amounts of rain in a short period of time, creating large rivulets and swales in the terrain. It can also progress slowly, moving the soil gradually to a lower spot, eventually making sloped land incapable of supporting any type of vegetation. In addition to the mechanical erosion caused by rain and wind, rain also sometimes contains chemicals that break soil particles up, making them more susceptible to displacement, especially on hillsides. In areas that see little annual rainfall, the wind is the culprit, stripping the terrain bare in a relatively short time, and depositing the soil in drifts.

Management

• Sloping areas can be landscaped to minimize erosion and make it possible for certain types of plants to grow there. Terracing involves creating a series of steps in a hill by leveling areas off in a descending order, and bolstering them with stones, masonry or landscaping timbers. This practice reduces water erosion by distributing water more evenly among the various terraces. Another solution is to plant different species of ground-hugging plants and shrubs, ground-covers and shrubs and trees whose larger roots systems are more effective at anchoring the soil and preventing it from washing away.