Lecture 3 Tropical Plant Life

Question 1

Plant life forms (Synusiae) –> 生态群

Answer 1

– these are not taxonomic groups but are functional forms of plant

• Trees
• Shrubs
• Herbaceous plants (usually smaller)
• Vines (a woody vine is a liana)
• Epiphytes
• Hemi-epiphytes (e.g Strangler figs)
• Epiphylls

Question 2

Trees

Answer 2

• produce woody tissues
• secondary growth
• common threshold height to distinguish between shrub and tree
  If species can reach 5m or more in hight then is considered a tree–> quite arbitrary, but the biggest shrub usually cant reach more than 5m in height
• Trees main structural component in forest. Without trees = scrublands
• have repeatedly evolved in many groups: isnt 1 family tree of trees

Question 3

Scientific names for trees

Answer 3

Given forests may have 1000 tree species (Canada have about 400, Ontario has about 200)
Often doesn’t have common names for trees: so need to use scientific names:

• Latin names always consist of genus+species
• genus is capitalized
• species name (epithet) is not . E.g Drybalanops aromatica (it should be italicized)
• always italicized

Common to give a family name because families broader and people know them
- family names are not italicized

Also there are many species within a genus

• so sometimes dont know what the species is
• Drybalanops sp. know the genus but species isnt specified
• Drybalanops spp. More than one Drybalanops species there

Question 4

Are forests inevitable? –> importance of competition

Answer 4

• woody tissue has evolved many times
• thought to be inevitable evolutionary development because gives some plants big advantages over others
  • light
  • taller plants have advantage of accessing light and shading neighbors
• tree ferns
  • stem = composed of leaf bases (fronds)
  • fern on top and lumpy stem
• palms
• also many flowering plants

Question 5

Marginal cases of ‘trees’

Answer 5

Arbitrary threshold of what trees are:
- on Mount Kilimanjaro, have giant senecio –> intermediate trees?

Other marginal trees

• woody vines start as free standing and later develop into lianas
• also very large herbaceous plants –> bananas get really big but dont form wood.

Question 6

Shrubs and treelets

Answer 6

• Plants that from woody tissue but dont reach 5m
• shrubs usually have multiple stems at base but stem not utilized consistently
• in some forests many tree species that dont actually reach canopy
  • ~2-5m in height
  • sit in understorey

Question 7

Characteristics of shrubs and treelets

Answer 7

• produce flowers and fruits at small size
• shrubs:
  • usually have multiple stems at base/have vegetative reproduction
• Treelets:
  • Single- stemmed trees that dont reach large sizes
  • Ex: Cacao in Euphorbiacea family –> is where cocoa comes from

Question 8

Canopy layers Diagram

Answer 8

• Non-technical sources might see idealized concept of how tropical forests are structured
• might say there are 5 distinct layers
• in reality, clear strata in most tropical forests are not so easy to recognize and in some cases dont exist

Question 9

Typical lowland forest profile

Answer 9

• more formal way is to construct a profile diagram: locate crowns of trees
• from badas forest reserve in Brunei
  • have tall dipterocap trees(emergent)
  •but also intermediate height vegetation
• so strata not as clear as what is often shown

Question 10

Distinct strata in monodominant forest

Answer 10

• profiles differ among forests
• Mbau forest dominated by one species
  • Gilbertiodendron
  •Big trees all of same species
• so here, find really distinct canopy layer
• so some tropical forest (particularly those that dominated by single species) show distinct strata.

Question 11

Herbaceous plants

Answer 11

• often do find discrete herbaceous layer
• in addition to woody plants are plants that dont form woody structures
  • herbs
  • lack secondary growth
• Herbaceous plants can grow 4-5m in height maximum without forming wood
• EX: Banana trees:
  • Giant herb
  • Isn’t actually a tree
  • can chop them down in one slice
• other characteristics understorey plants: Fan palms: Licuala
  • Very common in understorey
  • get to be 4-5m tall
  • form distinct layer in understorey

Question 12

Comparison with temperate forests

Answer 12

Tropical forest:
- more tree species than herb species:
• ~400 species
• ~200 herb species

Temperate forest:
- more herb species than tree species
• ~ 15 tree species
•~ 150 herbs species

Really different in terms of ratio of things even compared to a ‘non-diverse’ tropical forest
Tropical and temperate forests pretty much have no species in common.

Question 13

Many ‘primitive’ plants in tropical understories

Answer 13

• often find ferns and fern allies (fern-like plants)
• selaginella: Iridescent leaves that look like fern but is in other group
• Bracken fern: one of only plant species to have almost global distribution: so do find it in forests in Ontario, and tropics.

Question 14

Parasitic saprophytic plants

Answer 14

• some plants don’t photosynthesize
• parasitic plants: EX: Rafflesia
  • Genus of plants that produce the largest flowers on the planet
  • ~40-50 spp of Rafflesia
  • all of them are obligate parasites on 1 genus of vines (tetrastigma)
  • always find a haustorium on rafflesia:
  = Modification of root that allows plant to penetrate into vascular system of host.
  So it can suck nutrients/phloem
  = True parasite
  • Have very narrow host range
  • so if need giant flowers, means that we must also have vines for them to eat.

Question 15

Lianas

Answer 15

• woody vines
• germinate and establish on forest floor initially (free-living)
• eventually find trees and have climbing mechanisms for climbing up trees
• some reach canopy, some stay in understorey
• not true parasites:
  • dont tap into vascular tissue of host
  • but use host for structural support = pretty negative effect on host
• but some lianas are as important as commodities.

Question 16

Typical liana life cycle

Answer 16

• Lianas germinate on forest floor
• initially self- supporting
• when they grow toward dark things:
  • most plants grow toward the window (positive phototropism)
• Lianas when small have negative phototropism (skototropism)
  •Mechanism for finding dark places
  •Places consistently dark are usually where there is a big tree trunk
  • Liana knows this
• attach to tree trunk up to canopy
• once they’ve attached change to have positive phototropism
• most only produce flowers and fruits when up in the over-storey

Question 17

Climbing mechanisms

Answer 17

• some have root structures that attached
• some have tendrils
• some have hooks
• sometimes stem is modified to wrap around plants

Question 18

Epiphytes

Answer 18

• plants that grow on other plants: dont climb, just stay put
• initially deposited in canopy
• Often bird-dispersed
• wide variety of ferns, bromeliads, orchids, mosses (mostly in high elevation forests)
• usually growing in places where there’s not much soil
  • so have adaptations to deal with low nutrient inputs and periodic drought
  • no soil reservoirs to hold water

Question 19

Epiphyte common metabolic trick

Answer 19

- CAM  photosynthesis 
• keep stomates closed in daytime 
• only open at night to allow CO2 in
• initially fix CO2 into acids 
• Mobilize acids during day and re-fix CO2 using main metabolic machinery that most plants (C3 have) 

• Helps deal with drought- prone environments

Question 20

Epiphylls

Answer 20

• plants grown on other plants:
  • but rather than growing on woody parts of trees (epiphytes)
  • grow on leaves
• include algae, liverworts, lichens, mosses that grow on leaves
• epi= grow on, Phyll= leaves
• common in tropical forests especially when leaves are longer lived
• usually smaller sized
• trees that are late- successional (characteristic of old-growth forest) tend to have long-lived leaves = habitat for lots of Epiphylls
• pioneer species that come into open areas have short-lived leaves
• secondary forest: leaves are short-lived
  • if no Epiphylls probably secondary forest.

Question 21

Hemipiphytes

Answer 21

• start up in canopy like epiphyte
• but then roots grow down stem and get into soil
• some of them stay like that
• but some them take over host tree:
  • have root structures that completely cover stem of host tree
  • leaf structures grow out and take over canopy space
  • eventually gigantic strangular figs take position of host tree in canopy
  • host tree dies off
  • get decayed host tree stem

Question 22

Hemiepiphytic figs

Answer 22

About 900 species of them
 Very ecologically important
 Are pollinated by minute fig wasps
o Very specialized mating system involving fig wasps
 Most species of tropical trees flower and fruit synchronously
o Figs don’t do that
o Instead have asynchronous fruiting
o Flower independently, different trees flower at different times
o Some place in forest will probably be fig flowering
o So very important resource for fruit-eating animals
 If looking for birds and animals, should look for figs

Question 23

Lianas vs. epiphytes vs. hemiepiphytes

vs. epiphylls

Answer 23

check the table that compares all three of them

Question 24

Fig and Fig Wasp Life Cycle

Answer 24

 Female fig wasps exit fig after it falls off tree
 Fly up and cover kilometers to find other food
 Squeeze into other fruiting fig through small opening
o Often their wings are broken off
 Flowers of fig are inside of fig
 Wasps pollinate within flower (transferred pollen from other fig)
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 Lay eggs in host tissue
 So males and females develop within the fig
 Then mate within fig
 Fig trees also have 1:1 match between figs and fig wasps
 Every fig species has specific pollinator

Question 25

Figs as a “keystone resource”

Answer 25

 Often in tropical forests there isn’t a lot of fruit
 Exception:
o Figs
o Often in fruit all the time
 Frugivores (especially larger ones) are often fig specialists
o Parrots
o Toucans
o Hornbills
o Fig specialists
o Monkeys/other primates
 If in forest and hear loud squawking birds and primate calls probably will find figs

Question 26

Competitive displacement by larger species

Answer 26

 In Africa studies looking at primates and utilization of figs
 Pecking order:
o Small monkeys (Guenons) usually find fig trees first
o Larger mangabeys listen for Guenons to find fig trees, then boot the Geunons out
o Chimps hear mangabeys and boot mangabeys out

Question 27

Other “keystone” resources

Answer 27

 Fig = resource for frugivores when aren’t many resources
 But there are other “keystone” species
 EX: Fast-growing gap-dependent/secondary forest species to produce year-round
o Musanga tree
 Fall-back resource if no figs
 Great blue turaco specializes on fruits
 EX: Some understorey species produces a lot of fruits
o Some species in Rubiaceae
 But fig trees often most importan

Question 28

Dipterocarps

Answer 28

 Southeast Asia often dominated by single family called Diperocarpaceae (Dipterocarps)
 These are gigantic trees (~80-90 m in height)
o = Forests of SE Asia are usually twice height of forests in Central Amazonia
o Family of trees that are dominant also show masting behaviour
 Only fruit every 5-7 years
 Exaggerates importance of keystone species
o Because no fruit for long time, then suddenly a lot
 Dipterocarp canopy world quite different from understorey
o Many canopy specialists have evolved
o Flying frogs, flying snakes, flying lizards

Question 29

Di-ptero-carp = 2-winged fruit

Answer 29

 Fruit have 2 wings
o But some have 5 wings
 Dipterocarp wood highly valued for wood/timber
 Sensitive system because really big system and long intervals between fruiting events

Question 30

Dipterocarp seedlings after mast fruiting event

Answer 30

 After get blanket of dipterocarp seedlings but eventually die off

Question 31

Leaves opposite vs alternate

Answer 31

 Woody stem and leaves arranged either attached to same point or aren’t

Question 32

Simple vs compound

Answer 32

 Sometimes have leaves that are compound
 Entire structure produced at same time
 Whole leaf is divided (like a fern)
 Leaf composed of several leaflets
 So should always make sure what you’re calling a leaf is a leaf not a leaflet
 Can have alternate leaflets along rachis of leaf but leaf is opposite

Question 33

Reproductive parts give critical information

Answer 33

 Flowers and fruits (reproductive structures)
o Yellow: Giant palm flower structures
o Figs
 If you see reproductive structures can probably give good botanical names

Question 34

Some tropical trees to know
Common, widespread, easy to identify, tell you about the forest
[1] Cecropia spp.

Answer 34

 Most characteristic pioneer species that comes into open areas in tropics
 Have big fan-shaped leaves
 Gigantic leaves
 If look carefully:
o Base of stems
o The leaves are alternate
o Have some fruiting structures
o Also have ants that live on them
o Sparse looking ragged canopies
o Umbrella-like leaves
 If lots of them they’re a pioneer species that come in after big disturbance = secondary forest

Question 35

[2] Miconia spp.

Answer 35

 Opposite leaves
 Characteristic venation pattern (3-big veins)
 Then tertiary veins
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 Many species of it
o Some have purple underside
 Mostly pioneer trees (come into disturbed areas)
 Native to Neotropics but have spread

Question 36

[3] Inga spp.

Answer 36

 Inga is in the legume family (pea family)
 Has pinnate compound leaves
 Trees of various sizes
 Leaves themselves are alternate
 Along rachus has phalanges
 And if look really closely, have glands
o Glands visited by ants
 = extra-floral nectaries
o Mutualistic relationships
 Nitrogen-fixing
o Could be primary or secondary forest
 Compound leaves with phalanges
 In neotropics are the biggest genus of trees
o Trends to be more ingas than anything else
o = most speciose legume genus in Neotropics

Question 37

[4] Astrocaryum spp.

Answer 37

 Understory palms that grow in clumps
 Long pinnate compound leaves
 Very thorny trunk
 Overlapping thorns
o Really nasty
 If find palm, giant pinnate leaves
 Single bunch of leaves (monopodial)
 Widespread in secondary and primary forest

Question 38

[5] Ficus spp.

Answer 38

 Figs
 One of largest tropical genera -all over tropics
 Keystone
 If break leaf usually have sap (bleed white)
 Most are hemiepiphytes, but some free-standing trees
 Should look for terminal cone-shaped buds (Can also see figs)
 Fig venation patterns
 Alternate leaf patterns
 Figs are usually more abundant in primary forest
 Trees have to be established, then figs come in
 Takes time for figs to come in