Lecture 2 Tropical Forests And Their Role In The History Of Ideas Flashcards
Exaggerated tales of tropical forests
For Europeans + North asians forests were exotic
- -> many erroneous ideas
- -> people thought they were really chaotic
Vicious animals
- -> were dangerous places
- -> crazy wild beasts in there
- -> people thought would get attacks by apes
Impenetrable ‘jungle’ with vicious animals –> strong cultural images of forests
A common but non-scientific term –> ‘Jungle’
What does the word ‘Jungle’ actually mean?
- -> word is derived from Hindi word jangal which means desert: waste area, uncultivated
- -> doesnt have a formal scientific meaning
- -> so for this course we don’t use ‘Jungle’ in the essays
Species-poor with a uniform flora
Later on in European history were initial explorations in areas of tropics: coast of African, islands
People brought back coconuts and other species to European: bananas, Jack fruit, structures from red mangroves, sea almonds
Always brought same thins back from the tropics:
–> idea emerged that plants in the tropics were all the same
Where did the early explorers explore?
Scientists never went far inland
Basically just going to the beach
Even if they did go inland, –> met local people that had agricultural areas
But they didnt go back into forested areas
So came up with idea that there were just pan-tropical species that were everywhere in tropics
Thought there were a small number of species
But in tropics, things are actually quite different and very diverse between different tropics places.
Even great scientists make great mistakes
Carl Linnaeus (1707-1778)
Wrote a summary of tropical forests
What he wrote about tropical forests was pretty much fall wrong
The most famous tropical voyage in the history of science
Charles Darwin in 1840s on the beagle
Went to Galapagos
Voyage of the beagle (1831-1836)
- Didn’t visit Asian tropics, but went south through Australia and off coast of Africa
- this was not the first scientific voyage of discovery: darwin modeled his voyage after Alexander Von Humboldt
- Humboldt was darwin’s hero
Alexander Von Humboldt
Botanist
The world’s first international scientific expedition
- -Was launched in 1799
- -Went to Latin American to Orinoco river with Aime Bonpland
- -was first purely scientific expedition (which wasn’t the case with Darwin): before scientists usually go with explorers looking for gold/land
- had interdisciplinary scientific team: Botanist, zoologist, geologists
- first scientists go into real topics (not just going to beach)
- went to Andes, Orinoco and upper America
Excitement of tropics
Coconut trees
Foot high bouquet of flowers
Everything looked new to people on this expedition because no one had really ever ventured into rainforest before.
Route of Orinoco expedition
Coast of South America, Caribbean
Expedition made up hundreds of miles in Orinoco collecting thousands of species
Eventually went up into the Andes
Von Humboldt and the relationship between climate and vegetation
- Humboldt’s big achievement was a map of Chimborazo mountains in Andes
- if look at height of mountains in terms of being as as from the centre of the earth, Chimborazo is the tallest (taller than Everest, Everest s broad)
- Humboldt was the first to systematically link climate, soils, geology, vegetations
- going up Chimborazo, things higher on the mountain looked more similar to European plants (northern latitudes)
- first person to notice parallel between going up in elevation in tropics and going north in latitude
Orinoco flow: reverses direction
Sometimes flows in one direction, then switches
If have big rain in one area can have flow reversal –> remarkable geographical discovery
Von Humboldt’s legacy
- -concept of the scientific expedition
- made last major attempt to synthesize all scientific knowledge into 1 work (single work ‘Cosmos’)
- More geographical places named after von Humboldt than any other individuals in history
- inspired to next generation of scientists (including Darwin, Von Liebig and Wallace)
Charles Darwin and the voyage of the Beagle
- -Went to Galápagos Islands
- -noticed finches
- -gave him ideas for natural selection
- -sent finches specimens to John Gould who looked at patterns: was Gould that identified ‘Darwin’s’ finches and linked beak evolution to islands geography
- then later on, darwin interpreted patterns
Darwin’s unacknowledged source
– forester Patrick Matthew who didnt go to the tropics, worked in Europe
– did work on apple trees:
Noticed that if he planted cultivated apple trees back in forest, they died
By selecting trees that produce big apples, was diverting energy from other things in tree so couldnt compete in natural forests
So has to be natural process of selection analogous to cultivation that happens in wild to allow trees to survive (divisions between species not so clear)
– darwin did experiments on apple (grafting) that replicated things Matthew did
– so Patrick Matthew was actually the first guy to use word ‘Natural selection’
– Darwin never cited him because Matthew was a radical
Darwin’s legacy beyond natural selection
- -Foundations of community ecology: tangled bank limits population growth
- -earthworms and the biology of soil formation
- -pollination biology
- -sexual selection
- -structure of biological thinking and argumentation
- but natural selection not his originally
Other Great 19th century tropical biologists/explorers
Many biologists lose loves to research in tropics – from disease
Alfred Russel Wallace
–In spite of spending huge amounts of time in tropics lived to quite old
–collected more beetles than any single other person
–continued doing this in spite of first great beetle collection being lost in shipwreck
–Wallace laid foundations for natural history and biogeography for Southeast Asia (Malay Archipelago)
– Unlike Darwin who stayed on 1 boat, Wallace lived on the site for long time, met the local people:
Learned local languages
Took up culture in way that was unusual in 1800s.
Wallace and evolutionary biology
Discovered birds of paradise
Southeast Asia
- -Contributed to biogeography
- -started off close to Singapore, then to Borneo, then to Lombok island
- noticed species changed completely between islands
- went over narrow gap between 2 islands and almost no species in common
- -noticed differences were systematic
- -different set of species found in 2 close areas
Borneo vs Guinea
In Borneo find Gibbon, Broadbill, rhinoceros hornbill
In Guinea find tree Kangaroos, birds of paradise, parrots
Almost no overlap between biota in 2 islands
Why?
– separated on 2 different tectonic plates
–Wallace didnt actually figure this out but got really close
Tropical florist regions
- -completely different in 2 parts of tropics
- -tropics divided into 2 zones:
(1) new word tropics=Neotropics- -> sub-zones: Central America, South America
- -> in general, Central America has different species than South America
(2) Paleotropics
– > subzones:
Africa
Madagascar (own unique biological realm from Africa)
South Eastern Asia (Indonesia, Singapore, India etc):
(a) core area centered on Borneo
(b) North of this border, climate is really different : Monosoonal/seasonal forests
(c) also includes New Guinea: other side of Wallace’line
(d) New Caledonia: ecologically separated for long time from other continents
(e) Australia: small bit of tropical area in Australia
- across zones and sub-zones have few species in common:
- -> with exception of coconuts (which are very widely dispersed)
- -> in general, almost no overlap in biota of different areas
- across zones and sub-zones have few species in common:
- bur notice still some green in desert band areas (like Monsoonal Asia)
- -> mostly places with mountain ranges resulting in more unique and endemic species
- -> as get into areas with mountain ranges separating places, many more unique and endemic specie.
- bur notice still some green in desert band areas (like Monsoonal Asia)
Some of Wallace’s major contributions
- first to link geographic distributions to evolution
- first field observations on Orangutans
- -independent proposed natural selection, and co-authored paper with darwin which promoted the concept
- -collected >100000specimens from region known as ‘Wallacea’: most birds and insects
- -introduced concept of polymorphism
- -introduced concepts of functionality in animal coloration, including aposematic (warning) coloration: e.g Black and hello stripes on bees-toxic/dangerous organisms
- first proposed ‘green belts’ near urban areas: having conservation areas
- introduced statistical methods in epidemiology
- -concept of ‘exobiology’: extra-terrestrial origin of life on earth: there is an extra-terrestrial origin for life on earth = seeding of life from other planets
Two more Wallace contributions:
‘‘The museum ‘diorama’”
“Recognition marks’ in natural history
- Diorama:
First person to come up with museum diorama
Allow us to see where organisms live in museums instead of seeing bunch of dead animas in glass boxes - Recognition marks
First to use recognition marks that are used in natural history works
Establishing what you have to look for to identify species in the fields: distinguishing characteristics of species.
Truth about tropics forests
- are not impenetrable ‘jungles’ or fruit-filled gardens of Eden
- -most diverse/complex ecosystems on planet
- -Huge variation from place to place
- -understood mostly through collaborative sciences
- -rapidly declining due to human population pressure and patterns of resource use
- -represent one of the most important scientific and social challenges to the human species.
Global distribution of forests
- -area of forest in northern hemisphere
- -south of it is band of deserts
- -at equator is another area of forested area
- -go south again is another band of deserts
- -further south is subtle band of vegetation
Latitudinal gradients in forest types
- northern and southern bands corresponds to boreal and temperate forest:
(a) these are divided geographically by dry and tropical areas
(b) most of northern forest is giant Eurasian chunk of forest –> very continuous
- northern and southern bands corresponds to boreal and temperate forest:
- tropical forests:
(a) few species in common between tropical and temperate /boreal forests
(b) whereas have more similar species between temperate/boreal forests.
- tropical forests:
- -tropics forests more broken up:
(a) no land bridge between them (no continuous)
(b) lots of geographic separation for things to evolve separately
(c) so lots of moss species that are the same across Canada, Russia, Scandinavia
(d) but almost nothing like that in tropics
What determines the global distribution of vegetation types?
- Temperature: as Humboldt said
- Rainforest (total amount and seasonality)
- Soils
- Natural disturbance regime (wind, fire): say recent hurricane struck, then forest will look different
- Human activities
Latitudinal variation in solar energy
More energy from sun at equator than northern latitudes
Pattern driven by geometry (check the equation)
At equator, sunlight spread out over narrower range
Towards pole, same flux of energy projected over larger surface area
If you’re north of Tropic of Capricorn, sun is never directly ahead
So difference in energy =first part of explaining pattern
Diurnal variation in light
Truncated sine wave function
Clouds interfere
But maximum light follows half of sine wave
What are mountain tops cool?
Ideal gas law PV=nRT T=PV/nR Pressure goes down: -->Lower pressure as go up in elevation -->change in pressure results in changes of temperature: other things stay constant
Adiabatic cooling (or adiabatic lapse) 'Adiabatic' =not involving work
Change in temperature
Approximately relationships:
–> if have dry air and go up 100m, will have decline of 1 Celsius: 1C/100m
–>if have moist air only decline 0.6 for every 100m: 0.6C/100m
Water molecules in air gain heat of condensation
Phase change of water involves a lot of energy
So partially offsets adiabatic cooling
Using Adiabatic lapse rate
A math question , here you can skip
‘Hopkins’ Bioclimatic law
–If go from equator north or south get progressive decline in temperatures
– loser to equator, 120 m of elevation =1 degree of latitude
–Andrew Hopkins came up with this relationship between elevation and latitude:
(a) came up with this by looking at patterns of plant distributions
(b)Manitoba maple:
Common in waste areas in Toronto
If climb up mountains in southern Mexico, will find it.
Might also found other maples
Precipitation
Vegetation you find at a site is also determined by rainfall
Fundamentally all plants require water
Water has to come from precipitation
Plants and soils can store water but have limited capacity: so if have variable rainfall, plants that can store will maintain water
But in general, seasonality and total amount of rainfall are important
Climate Diagrams (Klimadiagrams)
- German came up with it
-divid monthly rainfall totals into areas considered wet, dry and drought - Wet period:
(a) Rainfall exceeds potential evapotranspiration
(b) corresponds to ~100 mm of rain paper month - dry period:
System likely to lose more water than gains but not whole lot more - drought period:
Less than 50 mm or rain per month
Might be affected by temperature regime too - could have areas that have similar total rainfall but different patterns (different seasonality)
- India:
Monsoonal period
Then really heavy rainfall
But very Singapore - Singapore
One of the least seasonal places on planet
Is wet but not hugely wet - so big differences in vegetation
Climatic variation in tropical Asia
- show areas close to equator in Southeast Asia: Singapore is the least seasonal
- northern areas:
monsoonal areas
Big annual seasonal changes in rainfall belts
Then pronounced dry season
Also in Australia - can map rainforests onto map
Usually to be considered rainforest, get ~1500 mm of rain per year
Aseasonal wet tropical forests include world’s most diverse forests
Area in Amazonian Ecuador
High diversity of plants
Very wet
Seasonal dry tropical forest has much lower diversity
Grass in understorey
Very different
Western Ghats, India
Far fewer species = enormous differences in diversity that track differences in climate
Seasonal vs aseasonal tropical forests
Seasonal tropical forest
- distinct dry/drought season (at least 2 months in direction)
- more deciduous trees:
(a) lose leaves during dry season = drought deciduous
- often have natural fire region:
EX: forests in Thailand and southeast Asian often have low level ground fires
- Trees are smaller
-lower tree species diversity
-higher Liana abundance = woody climbers
More light getting through and lianas need lots of sun
Aseasonal
- Often wet for whole time
- few deciduous trees
- fires of any sort uncommon
- larger trees
- high tree species diversity
- lower liana abundance
Some more basics of climatology
- All this energy coming into equator
- in addition to making it warmer on average, have a lot of chance for evaporation:
(a) Evaporation off water bodies (lakes, rivers, streams)
(b) Transpiration through leaves - results in lots of rising warm and moist air
(a) rising warm air cools according to adiabatic lapse rate
(b) water precipitates, and forms clouds
(c) thats why lots of clouds in tropics
Hadley cells
- general widespread circulation pattern
- areas right at equator where have maximum energy coming in and maximum evaporation = ITCZ
- pattern of air movement that is one of big climate patterns of planet
(a) as warm moist air rises, lots of rainfall precipitates out
(b) then air with rain squeezed out (so very dry) moves north and south and descends at 30 degrees’ latitude
(c) creates high pressure zone
(d) these are where the band of deserts lie - Hadley cell circulation gives rise to bands of wet forest and bands of desert
Global distribution of deserts
But some places still have forest even in the band of desert: especially Asia
Sub-tropical forests
- subtropics: more or less between 15-40N and S
- areas that if there weren’t ‘other things’ going on, they would be deserts:
(a) in general, these are mountainous places
(b) have forests coursing where there is sufficient moisture - big chunks of sub-tropical forests (China, Australia, Mexico etc)
- these areas receive moisture:
But often close to these areas also have hot dry areas
Rain shadows
- patterns is driven by rain shadows:
Rain shadow effect is pronounced in sub-tropical zones - have wind coming in and affecting patterns of rainfall close to mountains
- as air rises and cools (adiabatically), reach particular elevation where clouds form
(a) water in liquid form and condensation
(b) particular elevation band where lots of rain squeezed out of clouds
(c) so get forested area - above condensation level (cloud level), air cools at dry adiabatic lapse rate:
Above that band of clouds can be really cold, because lapse rate is higher - have dry air descending on other side of mountain
(a) all of that air is warming up at dry adiabatic lapse rate
(b) get pattern
(c) so as go over mountain to other side, is much hotter because of difference in wet and dry adiabatic rate - so subtropical forests can be quite wet, but found close to hot dry desert areas
Rain-shadow vegetation
- sparsely trees savannah
Rain shadow variation - is within close proximity of extremely wet high elevation forest
Tropical rainforest climate
- rainforest climates vary between major parts of tropics
- major biogeographic areas with little vegetation in common
- temperatures:
Don’t vary much
-solar radiation:
Don’t vary much - precipitation:
Huge variance
Amazonia has big range
East Malesia really wet
Africa, India, Australia are dryer areas: marginally about 1500 mm annually necessary for rainforest.
Soils.. why things arent so simple
- Differences in soil really contribute to wide range of vegetation
- comes out from weathering of geological material in combination with activities of plants (and animals to some extent)
- creates natural substrate for rooting of terrestrial vegetation
- in general, soil has to do with climate and vegetation
What else do trees need, beyond favorable temperature and water?
- plants need nutrients
- big 3:
N, P, K
In general, in tropics, there is high temperature and many ancient substrates
Nutrients leach out
P is only available from geological sources
So most tropical forests tend to be P limited
Whereas northern forests more nitrogen limited - but a lot of differences in soil in within tropics
Typical tropical soils
- highly weathered:
Hot; very cold; lots of water percolating through soil - reddish coloration because organic acids leaching things from soil = tropical soils usually red
- 2 main types of tropical soils
(1) Ultisols: red-clay soils, distinct A and B soils, Ult= ultimate product of weathering.(2) Oxisols
Ox from oxides of Fe and Al
More yellow-red due to more bioturbation
More bioturbation so no distinct horizons
More organism stirring up soil
What organism?
Giant tropical earthworms
Giant earthworm stirring soil
Bioturbation
Termites also help
Result in bioturbated oxisol soils
Health forest (kerangas)
- distinct forest vegetation
- depend on differences in soil and soil parent material
- health forest in Malaysia:
(1) tops of trees are about head-height =very depauperate forest
(2) find them on rocky substrates of sandy soils
(3) usually nitrogen limited
Tropical coastal forests
Distinctive Depauperate flora Same species occur from place to place Characteristic ocean-dispersed species Not very productive = issues with salt spray
Swamp forests
If go inland, find swamp forests
Forests with continuous or intermittent flooding
Swamp = wetland with trees
Main types of swamp forests:
(1) mangroves
(2) freshwater swamp forests
(3) Peat swamp forests
Vary depending on whether flooding happens often, and on saltMangroves and mangrove species
Mangrove
- associated with salt/brackish water
- formed pan-tropically in coastlines and estuaries
mangrove species:
- species are dispersed by sea water floating propagules: so many species have large distributions
- most common species are rhizophora and Avicenna:
(1) both global in distribution
(2) have weird roots
(3) root structures look like breathing tubes - species have adaptations to environment
(1) Pneumataphores = breathing tubes in roots to oxygenate them (since they are under water)
(2) Stilt roots: air channels, structures that anchor plants and oxygenate roots
Bruguiera
- weird reproductive biology
- many mangroves have fruits that actually germinate on the trees
- baby mangrove trees hang off other mangrove trees=viviparous seeding
- convenient from management perspective: can pull off seed, stick it mud.
Nipa
Salt water palms
Freshwater swamp forests
- No saltwater involved
- Flooded/periodically flooded forest type inland enough that no salt water intrusion
- many different kinds of swamp water forests
- depends if forests is in big estuaries, lake area, or little streams
- in Malaysia, small level streams dominated by certain plants
Varzea and Igapo
- many types of freshwater swamp forests
- Varzea:
(1) swamp forest types where have white water rivers
(2) white rivers from silt: have high pH, also high productivity
-Igapo
(1) forests that have black water rivers:
Like Rio Negro in amazon
Low pH
Lots of dissolved tannins from leaves
Lower productivity systems - middle picture
Silty river from varzea
Black water rivers so acidic that mosquitos cant breed in it.
Peat Swamp Forests
- rivers draining intact peat swamp forests are tannin-stained ‘blackwaters’
- big areas in SE Asia and New Guinea
- peat swamps have accumulation of undecomposed plant matter
Rooted in layers of peat
Gradual process
Are places where have gigantic peat formations (in Borneo) - Modern types of forests most similar to Carboniferous forests that give rise to oil reserves.
What is peat
Accumulated non-decomposed organic matter
Dig down into muck and find organic matter
Biodiversity and threads to peat swamp forests
- common organisms in undistributed peat swamp forests:
Sumatran Rhino
Proboscis Monkey
Bornean Swamp Toad - can deal with acidic conditions
- threats:
Clearing and draining, burning off peat to make shrimp ponds
Shrimp ponds gradually acidify, and become non-productive
Clearing for oil/palm developments
Peat fires
Characteristics changes in forest with increasing altitude
- shorter trees
- smaller leaves
- more epiphytes (especially mosses)
- trees more gnarled: stems less straight
- big changes in species composition: = latitudinal variation
More plants related to temperate zones: conifers, Ericaceae (blueberry family), Fagaceae (beech)
Cross section slide
- lowland rain forest: really tall
- lower montane forest: shorter but still multiple layers, often tree ferns
- lower montane cloud forest: often particular areas where cloud forms; cloud forest
- upper montane cloud forest
- subalpine cloud forest:
High elevation forests sometimes called elfin forests - have full altitudinal gradient in forest structure
Cloud forest
Not actually that diverse Convergent to temperate forest 40-50 tree species rather than 100 Shorter trees Lots of moss converted trees Not many lianas Relatively low diversity, but really specialized unique species One mountain might have different set of species than another
Key physiognomic characteristics of tropical forest types
Make sure to check out the diagram
Tropical dry forest has most lianas
