Geographic Zonation: Latitudinal and Vertical Belts

What is zonation?

Zonation (also called zonality) means that natural features change in belts or zones. Each zone has similar temperature, rainfall, soil and plants.

Why does it happen? Heat from the Sun is the main reason. The Earth is round, so the Sun heats places unevenly. Heat decides climate. Climate decides plants and soil.

There are two main kinds that you must know:

• Latitudinal zonation: belts that stretch east-west and change as you go from the equator to the poles.
• Vertical (altitudinal) zonation: belts stacked one above another as you go up a mountain.

Latitudinal zonation

At the equator the Sun is high in the sky, so its rays fall nearly straight down and warm a small area. Near the poles the rays are slanted and spread over a larger area, so each square metre gets less heat. That is why temperature falls as latitude rises.

Natural belts follow the heat and rain. In a simple ideal pattern, from the equator towards the north pole:

• Equatorial belt: hot and wet all year, rainforest.
• Tropical belt: hot, with wet and dry seasons, savanna grass and monsoon forest.
• Subtropical dry belt: sinking dry air, so deserts and scrub in many places.
• Temperate belt: four seasons, broad-leaf and mixed forest or grassland.
• Cold temperate (subarctic) belt: long cold winters, taiga (conifer forest).
• Polar belt: very cold, tundra and ice.

The southern half has the same belts in mirror image. Real maps are not perfect stripes. Oceans, mountains and ocean currents bend the belts. Land and sea also cause differences from east to west at the same latitude (a coast can be wet while the inside of a continent is dry). Features that do not follow belts at all are called non-zonal, for example a mountain range or a volcanic island.

Vertical zonation

Air gets thinner and cooler as you go up. On average, temperature falls by about 6.5 °C for every 1 km of height. This is called the lapse rate.

So a high mountain has a stack of belts. On a mountain at the equator, from foot to top:

• Tropical rainforest at the base.
• Broad-leaf (montane) forest.
• Conifer forest.
• Alpine meadow and bare rock.
• Snow and ice on top.

The line above which snow stays all year is the snow line. It is high near the equator (about 4.5 to 5 km) and low near the poles (near sea level). So the same mountain type gives fewer belts and a lower snow line as you move poleward.

Other things matter too. The slope facing the Sun is warmer than the slope in shade. The slope facing the rain-bringing wind is wetter than the dry slope on the other side. That is why belts on two sides of a mountain can differ.

Try it

1. Shine a torch straight down on a table, then shine it at a slant. Which spot is brighter and smaller? Which is dim and wide? This is the equator versus the pole.
2. In the 3D, pick "The equator" and slide up to 4 km. What is the belt? Now pick "Near the pole". At what height does the snow start?
3. Predict first: at 2 km height from sea level, what is the temperature if the sea level is 27 °C? Then check with the slider.

Key formulas and definitions

• Temperature at height h (km) = temperature at sea level − 6.5 × h
• Lapse rate = 6.5 °C per km (about 1 °C per 150 m)
• Snow line height = sea-level temperature ÷ 6.5 (in km, where temperature reaches 0 °C)
• Latitudinal zonation: belts change from equator to pole
• Vertical zonation: belts change from foot to top of a mountain

Worked examples

Common mistakes

• Thinking zonation means the same thing as climate. Climate is the cause; zonation is the belt pattern it creates.
• Thinking belts are perfect stripes on the real world. Oceans, currents and mountains bend them.
• Forgetting that temperature falls with height, not just with latitude.
• Mixing up the two: latitudinal belts run east-west across the Earth; vertical belts are stacked on a mountain.