The 20 to 60 inches of precipitation is distributed evenly throughout the year. Many of the same genera, previously part of an Arcto-Tertiary Geoflora , are common to all three of the disjunct northern hemisphere expressions of this biome. Different species of these genera occur on each continent. Lichens and mosses also grow on the trunks of trees. Lianas such as wild grape, poison ivy, and Virginia creeper climb the trees to flower and fruit high in the forest canopy.
Broadleaf trees tend to be nutrient-demanding and their leaves bind the major nutrient bases.
Thus the litter under this forest is not as acidic as under needleleaf trees and aluminum and iron are not mobilized from the A horizon. The autumn leaf fall provides for an abundant and rich humus which begins to decay rapidly in spring just as the growing season begins. The humus content gives both A and B horizons a brown color. Ultisols replace alfisols in the southeastern US, where the older soils of unglaciated regions have been weathered to a much greater degree and are more completely leached than the younger soils to the north. Distinctive red or yellow subsoils have developed under the warmer climate.