in the tundra, permafrost - ground that remains frozen for two or more years at a time - limits the growth of plant roots and tends to keep water close to the surface. therefore, trees cannot grow on it. however, above the permafrost, a layer of soil about 1.5 to 16.5 feet (0.5 to 5 meters) thick freezes and thaws enough to permit low-lying bushes, grasses, and wildflowers to grow. in the summer, the tundra comes alive with such plants as Arctic willow, crowberry, dwarf Arctic birch, and dwarf blueberry.
-world book
