Lecture 4: Gap Dynamics

Question 1

In the 1930’s Aubreville proposed ___

Answer 1

‘gap mosaic’ model in which the forest cycles through 3 main stages

Question 2

3 main stages of ‘gap mosaic’ model

Answer 2

1) gap creation: immediately following a tree fall or gap opening
2) Building or regeneration phase: which is characterised by competition for light & other resources leading to regeneration & growth
3) Mature phase: where the high emergent forest canopy is re-establsihed

Question 3

Gaps are a ___ part of forests dynamics

Answer 3

natural

Question 4

Forests are a mosaic of __ &__ at different stages of ____

Answer 4

gaps & trees and different stages of regeneration

Question 5

how are gaps created?

Answer 5

• rain forest trees will eventually die and fall, they may be uprooted or snap
• trees may be blown down
• struck by lightning& fall

Question 6

how does one tree falling cause so much destruction:

Answer 6

• when one tree falls it often brings many more as crowns are meshed together by lianas
• Large branches continually break off from trees and fall
• Gaps vary in size

Question 7

Damage to vegetation below varies with

Answer 7

gap size, composition of surrounding vegetation, type of forest

Question 8

gap fraction is defined as

Answer 8

the fraction of sky visible through the canopy

Question 9

Gap characteristics of different rain forest types ___

Answer 9

VARY

- Gap size & Gap fraction

Question 10

gaps create ___ microclimates affecting _______

Answer 10

diverse microclimates affecting light, moisture, temperature & wind conditions

Question 11

__ is the most limiting factor in the understorey of rain forests

Answer 11

Light

Question 12

full sunlight is approximately ___ micromoles/m^2/s on a sunny day

Answer 12

2000 micromoles/m^2/s

Question 13

At la Selva, Costa Rica gaps of approximately 300m^2 experience ___% of full sunlight compared to the understory which received ___ full sunlight

Answer 13

gaps = 8.6-24% 
understory = 0.4-2.4%

Question 14

Quality of ___ also changes with an increase in Photosynthetically Active Radiation (PAR) (400-700nm)

Answer 14

LIGHT

Question 15

Gaps receive differing levels of irradiance from…

Answer 15

full sun in the centre to shade at the edge

Question 16

Vapour Pressure Deficit, or VPD, is the

Answer 16

difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated

Question 17

once a gap opens competition for ___ & ____ is intense &____ take places

Answer 17

once a gap opens competition for light and nutrients is intense and rapid growth and reproduction take place

Question 18

there are different stages of succession within gaps:

Answer 18

-rapid colonisation by shrubs, vines, lianas & seedlings of PIONEER TREE species
-rapid growth of short lived light-daminding species which form canopy over 10-30years
-Slower growing shade tolerant (CLIMAX TRESS) species grow in biomass and species richness below the pioneer canopy & become taller. This phase transitions into the next phase when
-shorter lived species die & the more shade tolerant climax trees emerge & re-establish the tall canopy (can take 75-100 years )
HOWEVER LOT OF VARIATION IN THESE PATTERNS

Question 19

classification for pioneer and climax species:

Answer 19

• broad categorisation based on plant characteristics (functional traits) that influence growth & survival strategies
• pioneer-climax classification represent extremes on a continuum

Question 20

pioneer species typically produce:

Answer 20

lots of small seeds

Question 21

seeds of pioneer species are dispersed __

Answer 21

widely –> wind / animals

Question 22

pioneer genera are ___ distributed but species ___ as good dispersal tends to reduce the development of distinct populations

Answer 22

widely

poor

Question 23

pioneer: seeds can ____ in the soil seed bank until a gap opens producing favourable conditions for germination

Answer 23

lay dormant

Question 24

most pioneer species require __ to germinate and are ___

Answer 24

light and are gap - dependant

Question 25

pioneer species growth rates:

Answer 25

- typically establish and grow rapidly whilst light nutrients and water are available - high rates of photosynthesis & respiration that allows rapid growth under high light - leaves have a high hydraulic conductance' they transpire rapidly allowing high rates of photosynthesis - water us efficiency is low

Question 26

pioneer crowns are usually

Answer 26

open branched to capture light maximally

Question 27

leaves of pioneer species are usually quite

Answer 27

large for good light capture

Question 28

pioneer species leaf life span

Answer 28

short life span and turnover quite quickly

Question 29

pioneer species don't invest greatly in

Answer 29

defence against pathogens and herbivores

Question 30

pioneers hold a trade off between

Answer 30

growth & defence

Question 31

wood density of pioneer species

Answer 31

= low, have rapid growth rates

Question 32

pioneer species roots:

Answer 32

highly branched for efficient acquisition of nutrients

Question 33

pioneer can be m___

Answer 33

mycorrhizal

Question 34

how long do pioneer species typically live for?

Answer 34

10-30 years

Question 35

most pioneer species belong to

Answer 35

a few genera and families

Question 36

common genera of pioneer species:

Answer 36

- Cecropia - Musanga - Trema

Question 37

climax species: Seeds & germination

Answer 37

- seeds often large, produced annually / less frequently - often no dormancy - dispersal is usually short - germination occurs in understorey - soil seed bank contains few species - species may persist as seedling banks

Question 38

where do climax species usually germinate, establish and persist:

Answer 38

in shade below the canopy

Question 39

climax: survival in the understory is

Answer 39

ESSENTIAL

Question 40

climax seedlings can maintain themselves for

Answer 40

many years without putting on much growth waiting for a gap to open

Question 41

climax species have __ rates of photosynthesis and respiration compared to pioneer species

Answer 41

low

Question 42

climax species and transpiration

Answer 42

low rates of transpiration so they had a high WUE

Question 43

climax species often have _____ number of branches compare to pioneer species

Answer 43

greater number

Question 44

climax species leaves:

Answer 44

relatively small, long lived and with a slow rate of turnover

Question 45

climax and herbivores;

Answer 45

leaves are tough and contain chemical defences to deter herbivores

Question 46

climax species are adapted for

Answer 46

survival at the expense of rapid growth

Question 47

climax species and wood density

Answer 47

is high

Question 48

climax species roots

Answer 48

are mycorrhizal

Question 49

once the pioneer species die..

Answer 49

the climax species continue to grow and become the emergent canopy trees

Question 50

climax trees can live for

Answer 50

100 years

Question 51

evidence suggests that disturbance and diversity are related: Gap dynamics

Answer 51

‘Gap dynamics’ in forests fits with evidence that disturbance promotes diversity i.e. - Species may be adapted to exploit different stages of succession from gap opening to closing - This generates diversity in species number and ecological strategies

Question 52

what is the crown illumination index

Answer 52

(CII) is a visual estimate of the amount of light received by the tree crown

Question 53

Ignore

Answer 53

s