 Boreal conditions can be found across northern North America and Eurasia.The boreal forests in the interior of the continents grow on top of permafrost due to very cold winters (see drunken trees), while much of the boreal forest has patchy permafrost or lack permafrost completely.The short (3–4 month) growing season in boreal forests is sustained by greater levels of rainfall (between per year) than the tundra receives; This biome is dominated by closed canopy forests of evergreen conifers, especially spruces, fir, pine and tamarack with some diffuse-porous hardwoods.