Chapter 23 Terrestrial Ecosystems

CHAPTER 23: Terrestrial Ecosystems  Biomes o Classified according to predominant plant type o May be: 

Tropical forest

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Tropical Savanna

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Temperature forest

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Temperate Grasslands

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Conifer Forest

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Chaparral (shrublands)

(Taiga/Boreal Forest)

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Tundra

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Desert

 Robert Whittaker o Plotted biome types on gradients of annual temperature and precipitation o Pattern: 

Mean annual precipitation declines with decreasing temperature

23. 1 Terrestrial Ecosystems Reflect Adaptation of the Dominant Plant – Life Form  Leaves classified based on Longevity o Deciduous – lives for a year 

Based on Dormancy 

Winter-deciduous o Temperate areas



Drought – deciduous o Tropical areas

o Evergreen – lives beyond a year 

Broadleaf Evergreen Leaf 

No distinct growing season where photosynthesis and growth continue year round



Needle – Leaf Evergreen 

Growing season is very short



Nutrient availability constrains photosynthesis

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Adapted for survival

**Deciduous plants do not incur additional cost of maintenance and respiration when conditions restrict photosynthesis 23.2 Tropical Forests Characterize the Equatorial Zone  Tropical Rainforest o Latitudes 10o N and 10o S o Warm temperatures

o Amazon Rainforest 

Largest and most continuous region

o Mean Temperature: 18oC o Minimum Precipitation: 60mm  5 Vertical Layers in Tropical Rainforests: o Emergent Trees

o Shrub Understory

o Upper Canopy

o Ground Layer of Herbs and Ferns

o Lower Canopy  Buttresses o Large trees with plank-like outgrowths o Prop roots to support trees rooted in shallow soil that offer poor anchorage  Soil Classification o Oxisols 

Deeply weathered and no distinct horizon

o Ultisols 

More seasonal precipitation

o Andosols 

Ash deposits quickly weather

 Characteristics: o Warm, moist conditions o Rapid leaching o Strong chemical weathering o Decomposers consume dead organic matter rapidly  Dry Tropical Forests o Undergo dry season based on latitude o Influenced by Intertropical Convergence Zone 23.3 Tropical Savannas Are Characteristic of Semiarid Regions with Seasonal Rainfall  Savanna o Treeless areas of South America o Array of vegetation and open grassland, shrubs and trees o Moisture controls density of woody vegetation 

Function of rainfall

o Seasonality in precipitation o Max temperatures occur at end of wet season  Soils in Savannas o Nutrient – Poor Oxisols 

Deficient in Phosphorus

o Alfisols o Entisols 

Driest savannas

 Fire adapted, grass cover with or without woody vegetation always present  Savannas 2-Layer Vertical Structure o Ground cover of grasses o Presence of shrubs or trees  Tropical Savannas o Controlled by precipitation, changes soil moisture o Largely herbivores 

Ungulates

o Many insects 23.4 Grassland Ecosystems of the Temperate Zone Vary With Climate and Geography  Natural grasslands o Midlatitude in midcontinental regions where annual precipitation declines o Intervention of fire and human activity 

Shrunk to less than 12% of their original size

 Temperate grassland o Recurring drought  Native Grasslands distinguished by height: o Tallgrass Prairie 

Dominated by big bluestem

o Mixed-grass prairie 

Great Plains

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Composed of needle-grama grass

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Grading into desert

o Shortgrass Prairie 

Buffalo grass and forming blue grama

 Desert Grassland o With three-awn grass replaces buffalo grass o Annual Grassland 

Central valley of California



Rainy winters and hot, dry summers

 Steppes o Treeless, except for ribbons and patches of forest o Divided into 4 belts of latitude o Grasslands in Eurasia

 Pampas o Major Grasslands in South Hemisphere o Africa and S. America o Forage grasses and alfalfa  Velds o Southern Africa o Eastern Part of a High Plateau  Australia has 4 types of grasslands: o Arid Tussock Grassland (north; more than 20cm of rainfall) o Arid Hummock Grasslands (less 20cm rainfall) o Coastal Grasslands (tropical summer) o Subhumid Grasslands (coastal areas)  Animals in Grasslands: o Ungulates 

Eg. Bisons and antelopes

o Burrowing animals  Eurasian Steppes and Argentine Pampas o Lacks large ungulates o Has camels  Grasslands evolve over selective pressures of grazing o Grazing stimulates primary production  Major Consumption in grasslands are from: o Nematodes (belowground)  3 Strata in Grassland: o Crowns, Nodes and Rosettes of Plants hugging soil o Ground Layer o Belowground Root Layer 

Half the total plant biomass

 Grasslands accumulate a layer of mulch that retains moisture and turnovers fine roots o Depending on history and degree of grazing and fire  Soils in Grassland: o Mollisols 

Thick dark-brown to black surface



Rich in organic matter

 Productivity of Temperate Grasslands o Related to annual precipitation

23.5 Deserts Represent a Diverse Group of Ecosystems  Arid Regions/Deserts o 15o and 30o latitude  Tropical Deserts o ITCZ subsides to form high-pressure cells dominating climate  Temperate Deserts o Lie in rain shadow of mountain o Lack of precipitation o High temp summer, below freezing in winter  Sahara Desert o World’s largest desert in North Africa  Arid Coastal Regions o Cold ocean currents affect its development  Deserts of South Africa has 3 Regions: o Karoo o Namib Desert o Kalahari Desert  There are both hot and cold deserts  Cold Deserts o Great Basin of North America o Gobi o Takla Makan o Turkestan deserts of Asia  2 Main Vegetations in the Desert: (IDK SABI SA BOOK 2 MAIN VEGETATION PERO 3 YUNG NAKALIST NAKAKALOKA) o Sagebrush 

Forms pure stands

o Shadscale 

C4 species

o Chenopods 

Halophytes – tolerant of saline soils

 Hot Deserts Range from Lacking Vegetation to Combination of Chenopods  Drought – evading plants o Produce seeds when moisture and temperature are favorable  Drought – evading animals o Develop annual cycle of estivation or dormant state  Desert Plants

o Usually deep-rooted woody shrubs  Desert Ecosystems o Support rich animal life o Herbivores are generally opportunists o Animals practice omnivory  Primary Productivity is low o Infrequent rainfall o High rates of evaporation limit water availability  Islands of Fertility o Underneath plants in desert o Higher litter input and enrichment by wastes from animals 23.6 Mediterranean Climates Support Temperate Shrublands  Shrublands o Shrub growth either dominant or codominant o Fire is a frequent hazard  Shrub o Plant with multiple woody o Persistent stems o No central trunk  5 Regions of Mediterranean Ecosystems o North America o Central Chile o Cape area of South Africa o Southwestern Australia  Mediterranean Climate o Hot, dry summers o At least 1 month of drought and cool moist winters  Plants generally are: o dwarf trees known as sclerophyllous 

small leaves, thickened cuticles, hairs and sunken stomata 

all characteristics for reduced water loss from the hot dry weather

o broadleaf evergreen shrubs  Largest area of Mediterranean Ecosystem forms a discontinuous belt around the Mediterranean Sea  Fynbos o The vegetation is Mediterranean zone in southern Africa  Mallee o Mediterranean shrub community in Australia

o Dominated by Eucalyptus  Chaparral o California, North America o Sclerophyllous o Dominated by scrub oak  Mediterranean shrublands o Lack understory and ground litter o Highly flammable  Chaparral o Without fire it grows taller and denser 

Fuel loads of leaves and twigs

o Dry season; explodes when ignited  Animals (from parallel and convergent evolution) o Bird species o Lizard Species  Topography and Geology o Diversity of soil conditions  Soils: o Alfisols 

Deficient in nutrients

o Litter decomposition is limited by low temperatures 23.7 Forest Ecosystems Dominate the Wetter Regions of the Temperate Zone  Forest Ecosystems o Dominated by broadleaf deciduous trees o Southern Hemisphere 

temperate evergreen forests become predominant

 Asiatic Broadleaf Forest o Presence reflects transition into the Mediterranean region  Broadleaf Deciduous Forests o Temperate regions o Autumn colors of foliage  Deciduous Forests o 4 vertical layers or strata 

Upper canopy 

With dominant tree species

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Lower tree canopy/understory

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Shrub Layer

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Ground layer of herbs, ferns and mosses

o Greatest concentration and variety of life is below the ground layer  Soil Type: o Alfisols 

With glacial materials

o Inceptisols o Ultisols 23.8 Conifer Forests Dominate the Cool Temperate and Boreal Zones  Conifer Forests o Dominated by Needle – leaf evergreen trees  Sequoia o Largest tree of all o Grows in scattered groves on California Sierra  Boreal Forest or Taiga o Largest Expanse of Conifer Forest o Largest vegetation formation on Earth  3 Major Vegetation Zones of Taiga o Forest – Tundra Ecotone 

Open stands of spruce, lichens and moss

o Open Lichen Woodland 

Lichens and black spruce

o Main Boreal Forest  Boreal Forest/Taiga o Region of cold lakes, bogs, rivers and alder thickets o Under the controlling influence of permafrost 

Impedes infiltration and maintains high soil moisture

o Fire recurs in Taiga 

provides a seedbed for regeneration of trees

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Light fires favors hardwood species

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Severe fires eliminate hardwood competition and favor spruce and jack pine regeneration

 Permafrost o Frozen subsurface that may be hundreds of meters deep o Forces all water to remain and move above it  Interior Alaska and Central Siberia o Driest winters and greatest seasonal fluctuations o Max 100o C fluctuations

 Boreal Forests o Unique animal community o Caribou o Elk 

Largest of all deer

o Nesting ground for migratory neotropical birds o Low net primary productivity 

Limited by low nutrients



Cool temperatures

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Short growing season

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Rates of decomposition are slow under cold, wet conditions

23.9 Low Precipitation and Cold Temperatures Define the Arctic Tundra  Tundra o Top of Northern Hemisphere o Frozen plain in sedges, heaths and willows with lakes and crossed by streams o Finnish for tunturi which means a tree-less plain  Arctic Tundra o Falls into 2 broad types: 

Tundra with 100% plant cover and wet to moist soil



Polar Desert with less than 5% cover with dry soil

 Conditions unique to arctic tundra are the product of 3 interacting sources: o Permanently frozen deep layer of permafrost o Overlying active layer of organic matter and mineral soil 

Soil thaws each summer and freezes in winter

o Vegetation reduces warming and retards thawing in summer  Solifluction Terraces/ Flowing Soil o Downward flow of supersaturated soil over permafrost 

This rounds ridges and irregularities in topography

 Cryoplanation o Molding of landscape by frost action o (the rounding of ridges and irregularities of topography)  Animals: o Species tend to be low and growth is slow o Invertebrates concentrated near surface o Mostly have herbivores



Caribou 

Extensive grazers o Spread out in tundra



Musk ox 

Intensive grazers o Restricted to more localized areas

o

Major arctic carnivore: 

Wolf

 Plants: o Low ground is covered with grasses, sedges, sphagnum etc o Photosynthetically active, 3 months out of the year o Maximizes photosynthesis during the 24-hour day period o Most tundra vegetation is underground  Alpine tundra o Found at lower latitudes, occurs in higher mountains o Little permafrost o High elevation o Soils are drier o Precipitation, snowfall and humidity is higher than Arctic Tundra o Steep topography induces a rapid runoff of water