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Download Ecology 15 Forests, Woodlands and Savanna
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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 – – – – – 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 – – 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 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 – – – – 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 – – – – 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 – – – Low diversity of plants and animals Animals and plants well adapted Simple structure Productivity – – Low temperature Extreme seasonality Also polar desert
