Geology provides a foundation for natural communities by shaping the landscape and providing raw ingredients for soil formation.

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Geology and Landscape

Different plant species are at home on different parts of the landscape—whether mountain tops, cliff sides, rolling hills, deep coves, or floodplains. The features of a landscape are often determined by the type of bedrock underlying the land. For example, a solitary mountain or hill is usually made of rock that’s more resistant to erosion than the surrounding area. Rivers typically take the path of least resistance, carving valleys through weaker rock or sediment.

The geologic history of an area also helps shape the landscape, as continental collisions push up enormous mountain ranges, and the ever-changing sea erodes and deposits sediments.

The shape of the landscape creates microclimates that support different plants. Ecobit: Microclimates A mountain may be more exposed at the top, more sheltered at the base, warmer on its southern side, and colder on its northern side (assuming the mountain is in the northern hemisphere). Hence, you’ll find different natural communities at the top than at the base, and different natural communities on the north-facing side than on the south-facing side.

The shape of the landscape also plays a major role in soil accumulation. In a given region, relatively less soil will accumulate on steep or convex slopes as compared to level or concave surfaces. So if you’re looking for a plant that needs deep soil to sink its roots, explore a valley before looking on a cliff.

Geology and Soil Composition

In general, the composition of soil can be traced to the underlying geology, because that’s where many of the ingredients of soil originate. Different rocks contain different minerals, some of which are more or less useful to plants. For example, rocks high in basic minerals such as calcium and magnesium tend to create soil that supports a higher diversity of plant species than rocks deficient in these minerals. If you see two different natural communities in settings that appear similar, it may be that they are underlain by different types of bedrock.

Sometimes soil composition can be traced not to the underlying geology, but to the geology uphill. Imagine a mountain where the bedrock at the top is different than that at the bottom. The rock at the top weathers into fragments, which are pulled to the bottom by wind, rain, and gravity. There they break apart in place, creating a soil with ingredients from the higher elevation bedrock.

Geology and Soil Texture

Bedrock type also contributes to soil texture—that is, the size of the particles that make up the soil. Certain minerals, such as feldspar, tend to weather into very fine-grained particles called clay, which can trap a lot of moisture.

Where the soil is underlain by sediments and sedimentary rock, such as in the Atlantic Coastal Plain, the sediments are often incorporated into the soil, creating a coarse and well-drained soil.