The Impact of Topography on Natural Communities
Topography refers to the form of the landscape—its steepness, shape, and slope aspect (the direction a slope faces). Even within a relatively small area, variations in topography can create variations in temperature, moisture, and exposure to sun and wind. These differences create conditions that support different natural communities.
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How Topography Creates Microclimates
Topography creates differences in climate across very small distances. These differences in temperature, moisture, and exposure to wind and sun are called microclimates, and they are important predictors as to where various natural communities can be found.
For example, a windy hilltop with high evaporation and transpiration will tend to have a drier microclimate than a nearby sheltered ravine. Consequently, you’ll find plants on the ridge that can tolerate windy and dry conditions. In the ravine, you’ll find plants that prefer less windy and more moist conditions.
South-facing slopes will tend to be sunnier and drier than nearby north-facing slopes. That’s because the sun is always in the southern sky for those of us in the northern hemisphere. The sun’s rays strike a south-facing slope more directly than they strike a north-facing slope. This explains why snow melts away faster on south-facing slopes than on north-facing ones. It also explains why you’ll find plants adapted to sunny, drier conditions and warmer temperatures on south-facing slopes, while nearby north-facing slopes may contain plants suited to more shade, moisture, and cooler temperatures.
Slope shape is one of the biggest factors influencing natural communities.
A concave slope is like a bowl: it accumulates soil and moisture. A convex slope is the opposite. Turn that bowl upside-down. What happens? Precipitation runs off quickly, carrying soil with it. Water that does soak in drains through the soil rapidly, taking some of the soluble plant nutrients with it, leaving the soils dry and infertile.
Adding to the differences, in many cases convex slopes are at higher elevation than nearby concave slopes, and are thus more exposed to wind, sun, and lightning strikes. Concave slopes are more likely to be at lower elevations, closer to the water table and groundwater seeps and springs that contain dissolved minerals that help plants grow.
In general, hilltops and ridgetops are likely to be convex, while ravines and toeslopes are likely to be concave.
For all these reasons, convex slopes tend to have dry, infertile, and shallow soil that create challenging conditions for plants. Concave surfaces, on the other hand, tend to have deep, moist, fertile soils that support a wide variety of plant species.