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Biomes Chapter 23 Biomes Large scale patterns of terrestrial vegetation Biome distribution is determined by precipitation and temperature Biome vegetation types Trees, shrubs or grasses dominate each biome – Grasses allocate less carbon to structure than do woody plants – Shrubs allocate less to structure than trees Net cost must be positive – In adverse conditions (dry, low nutrient, cold, etc.), cost of maintaining woody tissue does not outweigh benefit Water Use Efficiency Grasses have greater water use efficiency than trees, which allows them to live in dry habitats – C4 photosynthesis versus C3 photosynthesis Biome leaf form Deciduous – Winter deciduous Cold winters – Drought deciduous Environments with distinct wet/dry seasons Biome leaf form Evergreen – Broadleaf evergreen No distinct growing season – Needle-leaf evergreen Cold and/or nutrient-poor environments with distinct seasons Climate diagram Tropical forests Restricted to equatorial zone Stable warm temperatures (~18°C) with abundant rainfall (>60mm month) High diversity Rapid decomposition Soils are oxisols and utisols, andosols in volcanic areas 90% of primates live in rainforests Distinct vertical stratification Lianas are abundant Strangler fig Dry or seasonal tropical forests Savanna Ground cover of grasses with scattered trees Distinct annual and interannual variation in rainfall Found on flat land surfaces with oxisols, alfisols and entisols Vegetation is fire adapted Vegetation determined primarily by moisture Deserts Found between 15° and 30° latitude Range of desert types – Cold deserts and hot deserts Temperate deserts are in rainshadows and areas with cold ocean currents Organisms exhibit drought tolerance or drought evasion Low productivity, omnivory and simple food webs Aridosols and entisols Shrub deserts Hot deserts Mediterranean Hot dry summers and cool moist winters Xeric broadleaf evergreen shrubs and dwarf schlerophyllus trees Adaptations to fire and low nutrients Sclerophyllous leaves Temperate forests Deciduous forests in northern latitudes and temperate evergreen in moist mild southern hemisphere Greatest diversity in ground layer Alfisols, Inceptisols and Ultisols Temperate forest communities Temperate rainforests Temperate deciduous forest Grasslands Rainfall is 250-800 mm Maintained through grazing and fire (and human activity) Greatest diversity and productivity where precipitation is highest and temperature is lowest Grasslands in North America Steppes Pampas Australian grasslands Grassveld Many grasslands today Productivity is related to precipitation Conifer forests Growing season short due to cold temperatures Boreal forest = taiga in this text Forest tundra ecotone in this text = taiga in other texts Short, cool, moist summers and long cold, dry winters (lots of snow) Presence of permafrost facilitates tree survival Fire adapted species Spodosols Animals Tundra Low precipitation and low temperature Low diversity and productivity Most of tundra vegetation is underground Freezing and thawing create landforms Animals Alpine tundra
