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Tropical Rainforest Biome"The land is one great, wild, untidy luxuriant hothouse, made by Nature for herself. . . How great would be the desire in every admirer of Nature to behold, if suchwere possible, the scenery of another planet! . . . Yet to every person it may trulybe said, that the glories of another world are opened to him"Charles Darwin in The Voyage of the Beagle"Never to have seen anthing but the temperate zone is to have lived on the fringe of the world"David FairchildTropical Rainforest Biome• associated with warm, moist tropical lowlands; equatorial rainbelt; short dry seasonsometimes• most diverse and structurally complex biome• multi-layered, evergeen canopy provides diversity of niches• recurrent structural and physiological adaptations to similar environments; these havearisen in quite different florasTropical Rainforest BiomeLocation: 1. Equator to 10° or 25° N & S latitude and 0 - 1,000m elevation inAmericas, Africa, SE AsiaTropical Rainforest BiomeLocation: 2. Along coasts windward to the trades — E. Brazil, Madagascar,NE AustraliaTropical Rainforest BiomeLocation: 3. East coasts with orographic precipitation — E. Panama andCosta Rica, E. Puerto RicoTropical Rainforest BiomeLocation: Seasonally dry tropical forests adjacent at higher latitudes or onleeward side of montane regionsTropical Rainforest BiomeThree floristically diverse regions:1. American: 50% of area2. African: 20%3. S.E. Asian - Pacific: 30%Tropical Rainforest BiomeFragmentation of rainforests —especially African and Asian —ongoingRemaining forests - 1999Tropical Rainforest BiomeRelationships to other tropical forest systems —elevation gradient:Tropical montane or cloud forestTropical Rainforest BiomeRelationships to other tropical forest systems —elevation gradient:Elfin forestTropical Rainforest BiomeRelationships to other tropical forest systems —elevation gradient:ParamoTropical Rainforest BiomeRelationships to other tropical forest systems —specialized swamp forests:Mangrove and beach forestsTropical Rainforest BiomeRelationships to other tropical forest systems —specialized swamp forests:Seasonally flooded swamp forestsRio Beni, BoliviaVárzea: flooded by muddy water tributariesof AmazonTropical Rainforest BiomeRelationships to other tropical forest systems —specialized swamp forests:Seasonally flooded swamp forestsVárzea: flooded by muddy water tributariesof Amazonflooded vs. dryTropical Rainforest BiomeRelationships to other tropical forest systems —specialized swamp forests:Seasonally flooded swamp forestsIgapó: flooded by nutrient poor waters ofsandy soils (leached tannin stained)Rio Negro, AmazonasTropical Rainforest BiomeTropical Rainforest BiomeRelationships to other tropical forest systems —latitudinal moisture gradient:Subtropical deciduous forests(& monsoon, tropical deciduous, thornforest)Alamos, MexicoSummer green, winter dryClimate• diurnal patterns (not seasonal)• 25° C mean annual temperature• daily convectional precipitation• 2 - 4 meters + rain Tropical Rainforest BiomeSoil• warm soil and water surplus promote rockdecomposition• reddish laterite soil• silica leached, Al + Fe left, acidic• well leached, no litterBrazil - after deforestation Hawaiian (Kauai - 5my) richer volcanic soilTropical Rainforest BiomeSoil• soil incapable of holding nutrient basecations• nutrients held in biomass• slash-burn agriculture quickly depletesnutrients in biomass and soilPanama slash burn agricultureBrazil cattle grazing followinglimited slash burn agricultureTropical Rainforest BiomeVegetation • warm & wet climate allows for broadleaf evergreenforest to dominate• net productivity is highest of terrestrial biomes• highest diversity (species number) of any biomeTropical Rainforest BiomeDiversity• 100,000 +/- species of floweringplants (40% of world’s angiospermflora)Greatest species diversity in wet tropicsAl Gentry (UW grad) holdsundescribed genus of liana• many undescribed or not discoveredTropical Rainforest BiomeDiversity• much of what we know in variousrainforests around the world comesfrom the Rapid Assessment Programof Conservation International• two of the leaders were Ted Parker (ornithologist) and Al Gentry (botanist)• they knew by sight (or sound) more tropical American birds and plants,respectively, than anyone else to dateTropical Rainforest BiomeGreatest species diversity in wet tropicsWhy this diversity? • general correlation with low latitude and rainfallTree species diversity in 1 hectare wet and dry forests around the world (Gentry)AmericanAfricanAsianwetdryTropical Rainforest BiomeWhy this diversity? • stable ecologically?• climatic change, allopatric speciation?• coevolution with animals?Virola (nutmeg family)Bird dispersed fruitsTropical Rainforest BiomeWhere is the diversity? in the tree strata primarily• 40 - 100 woody species per hectareAmazon Wisconsin60,000 spp. 2,000 spp.6,000 trees 50 treesTropical Rainforest BiomeFloristic dissimilarity of 3 regions• palms (Arecaceae) basically lacking in Africa (but not Madagascar) and diversein Malaysia and South AmericaMadagascar MalaysiaTropical Rainforest BiomeFloristic dissimilarity of 3 regions• dipterocarps (Dipterocarpaceae) diverse in SE Asia, lacking elsewhere• can form 80% of canopy• can form 40% of understoryDoes it suggest only ancient floristic linkageof tropical biomes?Dipterocarp forest in BorneoTropical Rainforest BiomeGentry tropical forest study sitesFloristic nature of 3 regionsSimilar families of trees involved ineach floristic region, but quitedifferent genera and speciesTropical Rainforest BiomeFloristic nature of 3 regionsAmericaAfricaAsiaAre families allowed only certain number ofspecies in each forest (Gentry hypothesis)?Tropical Rainforest BiomeStructure of the vegetation: TreesDense canopy in BorneoDense canopy in Costa Rica• tall trees form continuous canopy; therefore dense shade below• pervasive problem of extreme light at canopy vs. low light quantity within forestTropical Rainforest BiomeStructure of the vegetation: Trees. . . and low light quality within forestTropical Rainforest BiomeDense canopy in BorneoDense canopy in Borneo• struggle for quantity and quality of light hasgenerated numerous physiognomic andphysiological adaptations in unrelated speciesStructure of the vegetation: TreesTropical Rainforest Biome• tropical trees show characteristic shape and branching


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UW-Madison BOTANY 422 - Rainforest 1

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