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Forest Ecology > Production Ecology > Flashcards

Production Ecology Flashcards

1
Q

Define productivity

A

the accumulation of matter and energy in biomass in terms of carbon

ie., carbon is what is being exchanged/accumulated

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2
Q

Define primary productivity

A

photosynthesis

the conversion of light (electromagnetic) energy into chemical energy in the form of reduced carbon compounds

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3
Q

Define secondary productivity

A

When heterotrophs consume plant material and convert the energy (carbon) into their biomass

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4
Q

What is photosynthesis?

A

the process of converting light energy from the sun into chemical energy through atmospheric CO2 fixation

6 CO2 + 6 H2O + light –> C6H12O6 (glucose) + 6 O2

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5
Q

what is respiration?

A

the process that occurs in organisms to extract the energy fixed in the reduced (converted) carbon compounds

C6H12O6 + 6 O2 –> energy + 6 CO2 + 6 H2O

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6
Q

What is GPP?

A

gross primary productivity = the total amount of fixed CO2 by plants via photosynthesis by an ECOSYSTEM (large scale)

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7
Q

What is NPP?

A

net primary productivity = the total amount of fixed CO2 via photosynthesis MINUS plant respiration

aka the biomass increment

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8
Q

What measurement represents the biomass increment?

A

NPP

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9
Q

What is NEP?

A

net ecosystem productivity = the total amount of fixed CO2 via photosynthesis MINUS the total ecosystem respiration

aka the total carbon or biomass gained for an ecosystem

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10
Q

What measurement of productivity represents the total carbon or biomass gained for ecosystem ?

A

NEP

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11
Q

How abundant is carbon in relation to other elements in the universe?

A

it’s the 4th most abundant

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12
Q

T or F: C is the ‘backbone of life’

A

true

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13
Q

What components of the universe are involved in the global carbon cycle/biogeochemical cycle?

A

biosphere
pedosphere (skin of the earth)
geosphere
hydrosphere
atmosphere

and is the overall exchange of energy

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14
Q

What are the 2 elements of the carbon cycle?

A

fast and slow

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15
Q

Describe the slow carbon cycle briefly

A

takes 100-200 my to cycle C between the rocks, ocean, and atmosphere and moves a much smaller amount of carbon (10-100 Mt annually)

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16
Q

Describe the fast carbon cycle

A

takes ~90 yrs to move C through the biosphere (much shorter than slow)

moves 1000-100000 Mt of C per year (much more than slow)

C is fixed by autotrophs via photosynthesis
C is returned to atmosphere from respiration or fire

forests are key to this cycle

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17
Q

How are forests related to the fast carbon cycle?

A

45% of carbon stored on land is stored in forests

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18
Q

Where is the largest terrestrial natural storage sink of carbon on earth?

A

forests contain more C in biomass and soils than the atmosphere

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19
Q

What % of the Earth’s terrestrial area do forests cover?

A

~30%

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20
Q

What % of terrestrial GPP do forests produce? how much of the plant biomass on earth?

A

75% of GPP
80% of plant biomass on earth

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21
Q

Which forest types contain the most biomass? explain

A

tropical, moist intact forests
especially tropical peatland and mangroves due to their large storage of C in roots and soils

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22
Q

Which forest types have the lowest biomass? why?

A

boreal forests due to their low density of aboveground plant material

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23
Q

How do tropical peatlands and mangroves have such high carbon density if they’re tree biomass is low?

A

their roots and soils contain a high density of C even if the aboveground doesn’t

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24
Q

How much of the GPP does autotrophic respiration release? how does this affect NPP?

A

at least 50% of the CO2 fixed by plants is lost through respiration

so NPP = ~50% of GPP because P - R = NPP

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25
Q

What is the largest long term storage form of carbon in forests?

A

soil organic matter

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26
Q

What happens to most of the carbon fixed by primary producers?

A

lost as respiration from primary producers and heterotrophs and decomposers

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27
Q

~ how much energy is lost between trophic levels as respiration/heat?

A

90%

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28
Q

Of the NPP (CO2 fixed - respiration from plants), how much is consumed by heterotrophs? what happens to the rest?

A

~3% moves through the trophic levels
the rest is lost from the plant as litter and moves into the decomposition food chain

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29
Q

What contributes to the NEP?

A

litter and soil OM accumulation + live biomass accumulation of plants + consumers

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30
Q

WHat are the 2 largest components of NEP in forests?

A

litter and soil OM accumulation + live biomass accumulation of plants

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31
Q

T or F: plant respiration has a large influence on NEP - explain

A

true

deciduous forests have high plant biomass and therefore a high GPP, but because there’s so many plants, they have a high respiration cost = similar NEP to oak-pine forests that have much less plant biomass and lower GPP

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32
Q

explain why a deciduous forest with high plant biomass might have a similar NPP to an oak-pine forest with less plant biomass?

A

respiration!

the deciduous forest has more plants and a higher GPP but also that requires higher respiration rates = lower NPP

the oak-pine forest has less plants and lower GPP, less plants require lower respiration rates = higher NPP

these end up being relatively similar

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33
Q

What are the 2 components of total plant respiration?

A

respiration for construction and respiration for maintenance

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34
Q

How does NPP vary between ecosystems?

A

temperature and preciptation

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35
Q

Where is NPP highest globally?

A

closer to the equator

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36
Q

How does the NPP of forests compare to aquatic ecosystems?

A

NPP of forests are relatively high due to the generally large biomasses but some aquatic ecosystems have high NPP too (algal beds, reefs, estuaries)

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37
Q

Which terrestrial ecosystems have the highest NPP? the lowest?

A

swamps + marshes have highest
then tropical forests (highest forest)
then temperate forests
then boreal forests (lowest forest)
lowest overall is desert scrub

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38
Q

What infleunces the differences in ABOVEground NPP amongst forest types?

A

leaf area
water availability
nutrient availability
temperature
length of growing season

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39
Q

Why might coniferous forests have high NPPs comparable to tropical moist forests?

A

high leaf area of conifers

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40
Q

In what 5 pools does forest NEP accumulate in biomass?

A
  1. above + belowground tree and plant tissues
  2. above and belowground heterotrophic organism tissues
  3. woody debris
  4. forest floor
  5. mineral soil
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41
Q

Define biomass

A

the dry mass of living organisms and dead OM

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42
Q

How does the total distribution of biomass (between the 5 pools) vary for a boreal forest vs. a coniferous temperate vs. a deciduous temperate vs. a tropical wet forest?

A

boreal: most biomass is in the mineral soil (belowground) because of the VERY slow decomposition rate

coniferous temperate: most of the biomass is in the overstorey (trees) because of the very large and abundant trees

deciduous temp: almost an even distribution between overstory and mineral soil

tropical: huge proportion of the biomass is stored in the overstorey (but still a larger amount stored in soil than others) due to the rapid decomposition

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43
Q

Which forest ecosystems allocate the highest amount of NPP to roots?

A

boreal and tropical deciduous

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44
Q

Which forest ecosystems allocate the lowest amount of NPP to roots?

A

coniferous temperate and tropical evergreen (wet)

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45
Q

As PP increases, how does the allocation of NPP to different tissue types change?

A

generally, foliage remains similar
boles + branches decrease
and belowground (roots) decreases

46
Q

How much of NEP is belowground in a forest?

A

~75%

47
Q

What are the 5 levels of a trophic food chain?

A

1 = primary producer
2 = primary consumer (herbivores)
3 = secondary consumer (consume herbivores)
4 = tertiary consumer (secondary carnivores)
5 = apex predators

48
Q

Describe a food or trophic chain

A

a simplified sequence of how energy and nutrients are transferred within an ecosystem

49
Q

What is a food or trophic WEB?

A

an interconnected network of feeding relationships (ie., network of trophic chains)

50
Q

Where do decomposers fit into food chains?

A

at the end? because everything ends up being decomposed eventually?

along the side?

51
Q

what is the 10% rule?

A

~10% of the energy consumed at each trophic level is assimilated into the organism that consumed the other

~90% is lost as heat/respiration for metabolism and growth

52
Q

Which trophic levels help control lower level populations?

A

tertiary and apex predators

ex. wolves, eagles, weasels

53
Q

What is the food chain length based on? what does this measurement tell us?

A

the number of links between a trophic consumer and the bottom of the web

tells us about the transfer of energy and an indicator of ecological structure

54
Q

What is an energy/trophic/ecological pyramid?

A

a diagram of the flow of energy at each trophic level for an ecosystem

helps to demonstrate ecological efficiency at transferrin energy between trophic levels (~10% rule)

55
Q

How is an energy pyramid created?

A

based on a biomass pyramid

56
Q

Describe and compare the biomass pyramid for a pine forest’s detrital food web vs. grazing food web and the corresponding energy flow pyramids

A

Biomass:
- detrital: large base of PP, significantly smaller going up the trophic levels = very small biomass in fungi, soil herbivores
- grazing: small leaf biomass and VERY small up the chain

energy flow:
- MASSIVE base of energy
- detrital: huge amounts of energy in the trophic levels
- grazing: huge loss of energy between PP and consumers

===== although detritivores make up a small portion of the biomass in a pine forest, they play a huge role in energy transfer

57
Q

How are biomass pyramids infleunced at each level?

A

by the size of the organisms at each level

ex. because trees are huge, the PP biomass level of forests is usually very large, but as consumers (ex. insects) decrease in size, the pyramid steeply drops off

58
Q

What is the best model to convey energy flow? why?

A

energy/carbon flow models

biomass pyramids don’t convey the flux of energy and miss a lot of detail; energy flow pyramids are based off the biomass ones

59
Q

T or F: size and trophic position are strongly correlated in forest ecosystems

A

false - trees are massive but are PP

60
Q

Explain the forest energy/carbon flow model

A

high NPP = large biomass of plants
large amount of NPP from plants is transferred to detritus, some assimilated by herbivores

this supports a huge density of decomposers which pass on a fairly large amount of energy to predators

the small amount assimilated by herbivores supports a small amount of herbivores which pass on a relatively high amount to predators

61
Q

Where are the pools of C in the energy flow model for forests?

A

largest in autotrophs then detritus then decomposers then predators and smallest in herbivores

62
Q

What creates competition between species?

A

when species are in the same trophic level their niches may overlap if they use the same resource (if the resource is not limiting)

63
Q

What may plants be competing for?

A

light
nutrients
water

64
Q

What reduces direct interspecific competition?

A

territoriality and habitat selection (birds, mammals)

niche diversification (use same resource at different times) - ex. nocturnal v. diurnal

specialization for timing of food, type of food, place of feeding etc.

65
Q

What is the potential end result of diversification?

A

a keystone species that has a unique function

66
Q

What is a point of vulnerability in an ecosystem? why?

A

a keystone species because they perform a specific role which if lost, that function is also lost from the ecosystem

67
Q

What light wavelengths are photosynthetically active for plants (PAR)?

A

400-700 nm (visible wavelength spectrum) but specifically 400 and 750 nm

68
Q

Of the total incident energy (sunlight) on a leaf, how much is converted into a carbohydrate via photosynthesis?

A

~5%

69
Q

What influences the % of incident PAR energy (sunlight hitting the leaf) that is captured by plants?

A

photosynthetic efficiency

70
Q

What is photosynthetic efficiency?

A

Ps efficiency = NPP / incident PAR

how well a plant leaf can capture PAR energy and convert it into carbohydrates

71
Q

What determines Ps efficiency?

A

available resources = light, water, nutrients

72
Q

What does the proportion of PAR incident that is captured in a forest depend on?

A

plant density
leaf surface area per plant
leaf Ps efficiency

73
Q

What is the LAI?

A

the leaf area index aka = plant density + leaf surface area

LAI = project leaf surface area / unit ground surface area

74
Q

What determines LAI?

A

the available resources = light, water, nutrients (and the species type)

75
Q

How are LAI and Ps efficiency related to resource availability?

A

as resources increase, both increase but LAI increases faster

76
Q

How much of the captured energy in forests is lost to autotrophic respiration?

A

30-70%

77
Q

What factors influence autotrophic respiration?

A

temperature
plant size
growth rate
health

78
Q

What are the global trends for autotrophic R?

A

losses increase towards equator (warmer days + nights) = higher R rates

79
Q

What are the trends for stand age and autotrophic R? How does this affect NPP?

A

R losses increase with stand age (higher R rates) causing NPP to decline

stand age = increased woody tissue = a lot more tissue is non-photosynthetic but still requires maintenance

80
Q

Why would stand age cause increased respiration losses?

A

older trees have more woody tissues which do do not do photosynthesis but still require maintenance

81
Q

What does the alternative hypothesis state about how GPP, NPP and R are related to forest stand age?

A

all are declining

NPP declines because GPP is declining due to increasing age

more water stress?
nutrient allocation to more places?

82
Q

What form is most NPP lost in forests?

A

as litter (mostly leaf litter)

83
Q

How does litter loss trend globally?

A

increased litter loss towards equator
high growth = high litter loss

less litter is produced and lost in latitudes further from the equator where temperatures are cooler and soils are less rich in nutrients

84
Q

Where does most of the biomass turnover occur in most forests (above or belowground)?

A

belowground

85
Q

How does fine root litter production compare to leaf litter production?

A

fine root litter can be 40-330% more than leaf litter production

significantly higher turnover

86
Q

What is necromass?

A

dead organic matter in soils, litter, deadwood

87
Q

Is carbon in forest necromass or biomass larger globally?

A

necromass is larger
can account for ~58% of an ecosystem’s total carbon

88
Q

How does the boreal forests necromass compare to temperate forests? tropical?

A

necromass in boreal&raquo_space; temperate and tropical

temperate > tropical

89
Q

T or F: often in forest ecosystems, the detritus food web is most of the post-producer energy flow

A

true!!

90
Q

How do soil fauna increase the rate of decomposition? give examples of fauna

A

ex. worms, beetles, millipedes, springtails

degrade organic particles = increase SA

they remove wax and cuticles = easier to decompose

mix in organic particles into the mineral soil = increase moisture

91
Q

After soil fauna break down the organic particles, what follows in the detrital food chain?

A

bacteria and fungal decay!

92
Q

Why is bacterial decay faster than fungal?

A

bacteria love neutral pH and warm soils and can quickly decay high quality (angiosperm) litter but rely on soil fauna to first mix in the OM into the soil

fungi are good at decomposing in cold, acidic soils (slow) and more recalcitrant (lower quality) OM and can grow/reach OM without it being mixed into the soil

93
Q

who eats bacteria and fungi?

A

micro-invertebrates

94
Q

What is high quality litter?

A

LOW C:N ratio (more N per C) is easier to degrade

from angiosperms

95
Q

What 7 factors affect decomposition rates?

A

temp
moisture
pH
oxygen
soil fauna
chemical characteristics of litter
physical characteristics of litter

these all affect abundance of fungi and bacteria

96
Q

What is a LOW C:N ratio?

A

low N to C

25:1 or lower is optimal for decomposers

97
Q

Why is wood and bark decomposition slow?

A

because only fungi can do it
and because the C:N ratio is super high (500:1) - Nitrogen is super limiting here

98
Q

What are optimal conditions for decomposition?

A

5-80% water retention
2-40d C
proper aeration, not compacted or water logged
4-10 pH
low C:N ratio

99
Q

How does decomposition vary globally?

A

fastest at equator

100
Q

Where are forest floors the thickest, globally?

A

toward the poles (unless frequent fire) because of very SLOW decomposition

101
Q

How does plant type influence decomposition rates?

A

different plants will have different litter quality (C:N ratios) which will affect decomposition rates

102
Q

In what (general) ways might climate change effect forest productivity

A

changes to temperature, precipitation
seasonal shifts (frost delays, bud flush delays)
higher CO2 (improve water and N use)
disturbances (fires, floods, etc)
shifts in community structures - decomposition, transition from coniferous to deciduous?

103
Q

Why might NPP rise with increased CO2?

A

increase of CO2 in atmosphere allows for increased CO2 fixation by plants

104
Q

What kind of study designs were used to look at whether increased tree growth via CO2 fertilization can be sustained long term and be beneficial long term?

A

Free Air Carbon dioxide Enrichment (FACE) and Open Top studies to look at ecosystem level responses to experimentally increased CO2

105
Q

How is tree growth effected by increased CO2?

A

increased carbon availability and/or
increased water uptake and use efficiency (plants don’t have to open their stomata as wide or as long)

106
Q

In the meta-analysis of FACE and OTC studies, what did they find for above and belowground biomass and growth responses to increased CO2?

A

biomass increased significantly for both AG and BG
both showed greater growth with higher N

107
Q

Overall, how does increased CO2 affect the system?

A

increased plant growth = increased soil carbon input BUT

the effects of CO2 fertilization will be limited by nitrogen and will not be sustained because

when there’s high N = soil C input > C mineralization loss and there’s sequestration but

When N is limiting, the soil C input = the C mineralization adn there’s no sequestration (normal conditions)

SO only when there’s additional N or nutrients added to the system can N-fixers support high C sequestration

108
Q

What are the advantages and disadvantages of monoculture forests?

A

adv:
- easier to maintain
- plant species with desirable characteristics to improve growth rate + quality of wood
- even aged, high density, accessible = high yields
- efficient, uniform

dis:
- soil productivity and fertility can decrease
- disruption of hydro cycles
- risks of disease, invasives, lower resilience/resistance to disturbances
- reduce biodiversity of ecosystem

109
Q

What are the advantages and disadvantages of mixed-species forests?

A

adv:
- support greater biodiversity by creating more ecological niches
- more biodiversity = more productivity and stability
- more stable in response to disturbances and stresses (ex. resistance to fire or disease outbreak)

dis:
- lower tree growth
- lower species value

110
Q

Is a mixed or monoculture forest generally more productive? why?

A

mixed! because they can provide more resources and stability = more productivity overall

111
Q

in what situations will NPP be greater in a mixed stand than in a monoculture?

A
  • more resources = more efficient use of environment
  • mix of species is more stable against stresses

Forest Ecology (12 decks)

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