Alpine tundra

Alpine tundra is a unique natural biome found at high elevations.

This region is defined by the absence of trees. The harsh climate at high altitudes makes it impossible for large trees to survive. As you climb a mountain, you eventually cross the timberline. Below this line, you may see stunted forests called krummholz. Above the timberline, the landscape transitions into the alpine tundra. This zone continues upward until it reaches the snow line. At the snow line, ice and snow remain present even throughout the summer months.

The climate of the alpine tundra is driven by a process called adiabatic cooling. As air rises up a mountain, it expands and becomes colder. This is known as the dry adiabatic lapse rate. This rate is approximately 10 °C per kilometer of elevation. Because of this, climbing a mountain is similar to traveling toward a pole. Moving up a mountain is roughly equivalent to moving 80 kilometers toward a pole.

Local factors like proximity to oceans can change these patterns. The growing season is quite short, lasting only 45 to 90 days. Average summer temperatures are near 10 °C, but frost often occurs during the summer.

Scientists have developed several ways to define this specific climate.

Climatologist Wladimir Köppen noted that forests cannot grow if the warmest month averages below 10 °C. This is called a 10 °C summer isotherm. Otto Nordenskjöld later theorized that winter conditions also determine if trees can survive. He used a formula involving the average temperatures of the warmest and coldest months. In 1947, Holdridge improved these ideas by defining biotemperature. Biotemperature is the mean annual temperature where all temperatures below 0 °C are treated as zero. If the mean biotemperature is between 0 °C and 3 °C, the climate is classified as alpine.

Alpine tundra exists in mountain ranges across the entire globe.

Large regions appear in the North American Cordillera and the Appalachian Mountains. In Europe, it is found in the Alps and the Pyrenees. Massive areas exist in the Himalaya and Karakoram of Asia. You can also find it in the Andes of South America. Other locations include the Eastern Rift mountains of Africa and the Snowy Mountains of Australia. The landscape is often rugged with cliffs and rocky talus slopes. However, some areas feature gently rolling or even flat topography.

The plants in this biome have developed specialized survival strategies.

Most vegetation consists of perennial grasses, sedges, and forbs. These plants have more biomass in their roots and rhizomes than in their leaves. These underground parts help them store carbohydrates for the winter. Cushion plants are a common sight in the tundra. They grow in low, dense clumps to escape the high winds. Some plants have dense hairs on their leaves for protection. Others use red-colored pigments to turn sunlight into heat. These adaptations allow them to survive intense solar radiation and extreme cold.

Small changes in the landscape create a mosaic of different habitats.

A change in elevation of just one foot can alter the environment. One spot might be windswept and dry, while another nearby spot accumulates snow. This creates diverse microhabitats within a very small area. You might find cushion plants on rocky ridges. Grasses and sedges often grow along slopes. In bogs and near brooks, you may find mosses and low shrubs. Lichens also play a role, clinging to rocks and soil. These non-flowering organisms can photosynthesize at any temperature above 0 °C.

Because alpine tundras are geographically isolated, they host unique wildlife.

There is no single animal species that lives in every alpine tundra. Instead, different animals have evolved in different mountain ranges. You might find the snow leopard in some regions or the Himalayan tahr in others. Other animals include the mountain goat, pika, marmot, and yak. Even the kea and chinchilla inhabit these high places. While these animals seem hardy, the ecosystem is quite fragile. Repeated footsteps can destroy plants and cause soil erosion. It can take hundreds of years for the vegetation to recover.