Why do Arctic regions support scrubland instead of forests?

Arctic regions support scrubland instead of forests primarily because the climate is too cold or the warm growing season is too brief to permit the growth of trees. In these high-latitude environments, the tree line—the absolute northern limit of arboreal growth—is closely correlated with summer warmth, often coinciding with the 10 °C (50 °F) July isotherm.123

When temperatures are insufficient to support full-sized trees, woody species that might otherwise grow into forests are restricted to low, dwarfed, or prostrate shrub forms. These shrubs are better adapted to the harsh Arctic conditions, which include:23

• Short growing seasons: The limited time available for growth prevents trees from developing the necessary supportive tissues and energy reserves for annual reproduction.23
• Environmental stress: Arctic plants must endure permanently frozen ground, infertile soils, strong winds, and blowing snow.2
• Energy limitations: Low temperatures slow biological processes, reducing the production of dry matter and limiting the energy available for the development of large, erect woody structures.3

In these regions, shrubs become the dominant vegetation, forming extensive areas of Arctic scrubland in sheltered sites where conditions are slightly more favorable than in the surrounding polar deserts.12