Ecology 15 Forests, Woodlands and Savanna

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Ecology 15Forests, Woodlands and Savanna

• Ralph Kirby

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Ecosystems where trees are dominant or
codominantForests, Woodlands and Savannas

• Forests
• Where trees form a closed canopy
• Most widespread
• Requires enough moisture to support large trees
• Specific bands pole to equator
• Coniferous
• Temperate deciduous (warm and cool
• Tropical

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• Warm aseasonal environment
• Tropical Forest
• Evergreen broadleaf trees
• Seasonality
• Dry tropical forest
• Deciduous
• Coniferous
• Trees get smaller as seasonality increases
• Actual Evapotranspiration rate

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• Productivity and Decomposition increase as the
  places get warmer and wetter
• Note differences
• Litterfall
• Forest floor biomass
• Turnover time for decomposition

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Seasonality and Tropical Forest

• Tropical Forest has been divided into various
  types
• Boundary not clear
• Not continuous
• Broken by lack of moisture
• Tropical Rain Forest
• Lowland (lt1000 m)
• Mountain (gt1000 m)
• Cloud
• Very high altitude
• Swamp
• Wet soils
• Peat
• Nutrient Poor
• Tropical and Semi-tropical seasonal forests
• 2 to 4 month droughts
• Results in 30 loss of leaves
• Fruits at the sta

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• Tropical Rain Forest
• Very high diversity of microbial, plant and
  animal life
• 10 square km
• 1500 species of flowering plants
• 750 species of trees
• Richest Malaysia 7900 species
• Stratification
• Can be difficult to define
• Crowns of emergent tree
• Mop top trees
• Conical top trees
• Shrubs, young trees, tall herbs and ferns
• Tree seedlings, low herbaceous plants and low
  ferns

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• Many plants use the trees for support
• All shallow rooted
• Mycorrhirae are important
• Epiphytes
• Niche
• Stranglers
• Whole tree
• Climbers
• Usually where disturbed
• Continuous changes
• Trees die
• Trees fall
• Gap appear and disappear
• Stratification
• Supports greater diversity of animal life
• Above canopy group
• Insectivorous and carnivorous birds and bats
• Canopy group
• Birds, fruit bats, mammals who eat leaves and
  fruit

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Deciduous Forest

• Once covered most of Europe, China, North and
  South America
• Largely cleared by humans
• Remaining only semi natural with few exceptions
• Two Types
• Beech-Oak-Hornbeam
• Oak-Hornbeam
• More acid soils

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• Temperate Evergreen Forests in Subtropical areas
• Australia
• New Zealand
• Patagonia
• Temperate Deciduous Forest
• Four strata in uneven aged stands
• Even aged stands show poor separation
• Canopy of dominant and codominant trees
• Lower Tree Canopy
• Shrub Layer
• Ground layer
• Animals inhabit various layers but less diversity
  than tropical forest
• Light intensity in different areas varies with
  season
• Spring gives most light to ground
• Darkest for ground in midsummer
• Microclimate variation
• Highest temperatures in canopy
• Humidity varies with season
• Highest in summer

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Coniferous Forests

• Wide variety of environemnts
• Mountains
• Cool Temperate Regions
• Simple Vertical Structures
• Three types of crown
• Straight cylindrical trunks with varying crown
  density
• Scots pine
• Spiral shaped
• Douglas fir
• Cedars
• Deciduous conifers with pyramidal open crowns
• Larch
• Little vertical structure
• Sharp reduction in light
• Does not change
• Some stratification for birds
• Temperature variation
• Changes with type of forest
• Dominant in northern latitudes

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Boreal Forest

• Coniferous Forest that dominates northern
  latitudes
• 11 of terrestial surface
• Highly influenced by seasonal freezing and
  thawing
• Permafrost in north
• Wet in summer due to thawing
• Tundra southwards
• Forest-Tundra
• Open boreal
• Main boreal
• Boreal-mixed forest
• Simple Structure
• Spiral spruces and firs
• Open pines
• Larch
• Shallow roots
• Fire important
• Unique but simple animal community
• Large herbivores
• Ground birds

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Changes in Environment affect Forests

• High results in change from deciduous to
  coniferous
• Reduced soil moisture gives rise to woodlands in
  temperate regions
• Increased diversity of habitats and species
• Reduced soil moistures gives rise to savannas in
  tropics
• High biomass of grasses
• Still lots of trees but spread out
• Driven by seasonality
• Unique herbivores

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Grassland, Shrubland, Desert and Tundra

• Decrease in available water changes Forest to
  Grassland in Temperate zones
• 250mm to 800mm of rain
• Note difference between created and natural
  grasslands
• Europe stable
• America revert to forest
• Grasslands vary
• Tallgrass prairie
• Near forest
• Shortgrass prairie
• Great plains of US
• Desert grassland
• 300-400 mm rain
• Steppe
• Asia
• 500-600 mm rain
• Pampas
• South America
• 450-900 mm rain
• Veld

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• Vertical structure of grassland changes with
  season
• Various layers containing different plants
• As plants grow out of winter
• At the ground
• Light decreases
• Temperature decreases
• Humidity increases
• Wind decreases
• Thatch accumulates
• Slow decomposition
• 3 to 4 years
• Burning important
• Removes thatch and mulch
• As does grazing
• Complex root systems
• Half plant below ground

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• Natural and domestic grassland support a very
  wide diversity of life
• Large ungulates
• Example bison in US
• Eurasian too originally
• Africa Zebra, Rhino, etc
• Productivity and nutrient cycling controlled by
  drought
• Best gt800mm rain and gt15oC
• All grassland have evolved under grazing pressure
  together with drought

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Shrubland

• Difficult to characterize
• Created by man
• Created by disturbance
• Part of arid gradient
• Shrubs have an advantage over trees in arid areas
• Invest less energy above ground
• Better moisture collection
• Faster growth
• Mediterranean Shrubland
• Winter rainfall
• Broad leaf shrubs
• Dwarfed trees
• Heathland
• Cold type shrubland
• Nutriant poor, especially nitrogen and phosphorus
• Usually high altitude
• Dry Type
• Seasonal drought
• Wet Type

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Desert

• Diverse set of ecosystem
• Where evaporation exceeds rainfall
• Semi deserts
• 150 to 300 mm rain
• True deserts
• 70 to 150 mm rain
• Extreme deserts
• lt70 mm rain
• Simple physical structure
• Moisture limits production
• Plants and animals adapt to aridity
• Limited plant and animal diversity

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Tundra

• Low precipitation
• Low temperature
• Permafrost
• 100 cover and moist
• Simple structure
• Low diversity of plants and animals
• Animals and plants well adapted
• Simple structure
• Productivity
• Low temperature
• Extreme seasonality
• Also polar desert