Biomes Definition: a major geographic region defined on the basis of dominant plant growth forms. Determinants: 1) Climate- particularly temperature and rainfall patterns; 2) Topography (landforms) and soils (edaphic factors): factors that secondarily influence the local distribution of organisms within biomes. Climatic zones: 1) boreal (mean <5ºC), 2) temperate (mean >5, <20 ºC), 3) tropical (mean >20ºC). The biome concept applies best to terrestrial systems.

Grouping Characteristics Plants and animals from different parts of the world often show similar characteristics if they are part of the same biome (character convergence). The catbird (upper right) of North America and the reed-warbler (lower right) of southeast Asia are ecologically equivalent species. They also show similar physiological adaptations. Plants further show similar growth forms.

Principal Biomes Tundra: Climate- polar Vegetation- treeless, low evergreen shrubs, herbs and lichens Limiting factor- permafrost Distribution- far northern hemisphere and alpine zones Animals- polar bear (right)

Principal Biomes Boreal Forest (Taiga): Climate- cool summer, long, cold winter Vegetation- evergreen and deciduous conifers Limiting factor- short growing season (10 weeks) Distribution- northern hemisphere and alpine zones Animals- blue-headed vireo (right).

Principal Biomes Temperate Grassland (Prairie): Climate- hot summer, cold winter (continental climate) Vegetation- grasses and forbs; trees along rivers (riparian forest) Limiting factor- annual rainfall about 10” Distribution- centers of continents Animals- bison (above), prairie dog (left)

Principal Biomes Temperate Seasonal Forest: Climate- moderate; winter mean >-20ºF Vegetation- deciduous trees Limiting factor- 17 week growing season Distribution- eastern North America, western Europe, Korea Animals- red-spotted newt (right)

Principal Biomes Temperate Rainforest: Climate- mild and wet Vegetation- large conifers Limiting factor- summer rain and fog Distribution- Pacific northwest, New Zealand, S. South America Animals- ruby-crowned kinglet

Principal Biomes Shrubland (Chaparral): Climate- summer drought, rainy winter Vegetation- waxy-leaved, evergreen shrubs Limiting factor- frequent fires Distribution- S. California, Mediterranean, S. Australia Animals- western tanager (left)

Principal Biomes Subtropical Desert: Climate- very dry, high daytime temperature Vegetation- sparse, with drought-resistant leaves Limiting factor- heat, dryness Distribution- southwestern North America, central Africa, central Asia Animals- spadefoot toad (left)

Principal Biomes Tropical Savannah: Climate- rainy summer, dry winter Vegetation- grasslands with park-like stands of trees Limiting factor- limited rainfall Distribution- Mexico, S. Africa, SE Asia, N. Australia, E. S. America Animals- burrowing owl (right)

Principal Biomes Tropical Rainforest: Climate- uniform hot, wet and dry seasons Vegetation- diverse tropical hardwoods and vines Limiting factor- heavy rainfall and uniform high temperatures Distribution- N. S. America, W. Africa, SE Asia Animals- fruit dove (right)

Alpine Zonation Increasing altitude mimics the effects of increasing latitude. At higher altitudes in mountains, more northerly associated biomes are found. In the northeast, the lowest elevations of mountains have temperate seasonal forest, which is replaced by boreal forest at higher elevations, which is in turn replaced by alpine tundra. Near tree line (the highest elevation of tree growth), a stunted boreal forest called krummholz develops. Alpine biomes differ from latitudinal biomes in factors like day length and temperature variation.

Global Biome Distribution

Climatic Relationship of Biomes