Why do mountain ranges often contain different ecosystems on the same slope?

As altitude rises, temperature generally falls and exposure to wind increases, while precipitation patterns can shift with slope and aspect. This creates a series of ecological bands, from forest at lower elevations to alpine meadows and bare rock higher up. South-facing and north-facing slopes can also differ sharply in sunlight and moisture, especially in the Northern Hemisphere. Because of these gradients, mountains can pack a huge variety of life into a small area.