Direction of Mountain

The direction (aspect) a mountain slope faces has a real ecological effect, because the north-facing and south-facing sides of the very same hill can receive markedly different amounts of humidity, rainfall, light intensity, day length and temperature. As a result, the two faces of a single mountain can end up supporting quite different flora and fauna even though they are separated by only a few hundred metres of ridge-line. This same asymmetry also shows up at smaller scales — for instance, the centre and edge of a pond can differ in water depth (because of soil slope and differing wave action), which is enough on its own to give different parts of the same small water body distinct sets of resident species. A related idea is the ecotone, the transition zone between two adjoining ecosystems (for example, the border between forest and grassland), where species from both neighbouring habitats mix and where the local mix of environmental condition …