Soil Processes: A Place to Take Root

Natural processes that influence the texture, depth, composition, and moisture content of soil play a pivotal role in determining the locations of natural communities upon the landscape.

Convex slopes tend to have shallow soil because of slope processes that transport soil and leaf litter downhill. Moss grows well on the mineral soils that remain. To do well here, larger plants need to have robust, shallow root systems like American beech has (right). Mountain laurel shrubs (left) have a dense network of roots.
Photographer: Sam Sheline, courtesy of NatureServe
Exposure to weather, which is often a function of topography, helps determine moisture content, nutrient levels, and thickness. Soils on hilltops and upper slopes are often relatively dry because they are exposed to more sun and wind than soils in protected ravines. Furthermore, rainwater rushes off hilltops quickly, eroding soil and leaching away nutrients.

Even apart from rainwater, gravity and weather work together to transport material downhill by means of landslides, frost-heaving, and soil creep, all of which affect soil thickness. Upper slopes are areas of erosion, often resulting in shallow, droughty soils, whereas lower slopes or ravines are areas of soil accumulation, helping to build deep soils in concave areas along and at the base of a slope. Soils in these low, concave areas may have more moisture because rainwater has more time to soak in, and because they may be closer to streams and groundwater seeps.

In general, the nutrient composition of soil is largely determined by the mineral content of the underlying bedrock or sediments. However, downslope movement can bring rocks and soil from upslope that differ in composition from the underlying bedrock.

Read more about soil formation in Ecology Basics|Physical Setting.