Transcript Ecology 15 Forests, Woodlands and Savanna

Ecology 15
Forests, Woodlands and
Savanna
Ralph Kirby
Ecosystems where trees
are dominant or codominant
Forests, 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
Warm aseasonal
environment
– Tropical Forest
– Evergreen broadleaf
trees
Seasonality
– Dry tropical forest
– Deciduous
– Coniferous
Trees get smaller
as seasonality
increases
– Actual
Evapotranspiration
rate
Productivity and
Decomposition
increase as the
places get
warmer and
wetter
Note differences
– Litterfall
– Forest floor
biomass
– Turnover time for
decomposition
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 (<1000 m)
– Mountain (>1000 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
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
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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
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
Below canopy group
– Flying mammals, birds and bats
Middle group
– Squirrels and such that move between group and canopy
Forest Floor
– Large herbivores and carnivores
Ground Group
– Small insectivorous, herbivorous, carnivorous and omnivorous ammals
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
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
Higher during night than day
Coniferous Forests
Wide variety of
environemnts
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Mountains
Cool Temperate Regions
Simple Vertical Structures
–
Three types of crown
Straight cylindrical trunks
with varying crown density
–
Scots pine
Spiral shaped
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Douglas fir
Cedars
Deciduous conifers with
pyramidal open crowns
–
Larch
Little vertical structure
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Sharp reduction in light
Does not change
Some stratification for birds
Temperature variation
–
Changes with type of forest
Dominant in northern
latitudes
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
Some large carnviores
Herbivorous insects
Nesting ground of many neotropical and tropical birds
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
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High biomass of grasses
Still lots of trees but spread out
Driven by seasonality
Unique herbivores
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
– Southern Africa
– 1500-2000 metres
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
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 >800mm rain and
>15oC
All grassland have evolved
under grazing pressure
together with drought
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
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Cold type shrubland
Nutriant poor, especially nitrogen and phosphorus
Usually high altitude
Dry Type
Seasonal drought
– Wet Type
Seasonal waterlogging
Animal Community
– Small animals and ground birds
– Distinct to region
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
– <70 mm rain
Simple physical structure
Moisture limits production
Plants and animals adapt to aridity
Limited plant and animal diversity
Tundra
Low precipitation
Low temperature
Permafrost
100% cover and moist
Simple structure
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Low diversity of plants and animals
Animals and plants well adapted
Simple structure
Productivity
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Low temperature
Extreme seasonality
Also polar desert