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Boreal Ecology > Lecture 5 - Disturbance > Flashcards

Lecture 5 - Disturbance Flashcards

1
Q

Definition of disturbance

A

relatively discrete event in time and space that alters the structure of populations, communities, and ecosystems and/or changes resources, substrate availability, or the physical environment

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2
Q

examples of natural causes of disturbance

A 
fire
flooding
insect outbreaks
volcanoes
frostheave
ocean currents
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3
Q

examples of human cause disturbance

A 
agriculture
urbanization
logging/resource extraction
mining 
road construction
ecotourism
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4
Q

impacts of disturbance are influenced by what 3 general categories?

A

spatial factors
temporal factors
magnitude

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5
Q

describe the spatial factors influence disturbance

A

size
shape
connectivity
proximity to unaffected areas

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6
Q

describe the temporal factors influence disturbance

A

frequency
duration
time of year

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7
Q

what are the 3 most important natural disturbances in the boreal?

A

fire
insect infestations
severe weather

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8
Q

define succession

A

changes in equilibrium communities

replacement of one community to another

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9
Q

primary succession
vs
secondary succession

A

takes place on land where no organic soil exits
(ex glacier scrapes down to bedrock)

takes place after an ecological disturbance
*don’t take away all the soil

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10
Q

what is the most important cause of disturbance?

A

fire

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11
Q

what are two ways that fire is a primary agent of change in the boreal forest?

A
  1. releases nutrients
    - reduces litter on forest floor and release nutrients that have been tied up in those materials
  2. allows sunlight
    - opens up canopy to sunlight –> stimulates regeneration from seeds and roots
    - stimulates growth and reproduction
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12
Q

what causes fire?

A

lightning!

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13
Q

what percentage of total fires are made up by lightning?

why is it such a big factor?

A

35% of total fires
BUT
represents 85% of area burned

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14
Q

how will climate change impact lighting fires?

A

rising temperatures are expected to increase the number of lightning strikes
12% increase for each degree celsius

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15
Q

3 types of fires

A 
surface fires
-burn only on ground
crown fires
-burn only in canopy
ground fires
- burn along ground or underground
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16
Q

describe surface fires

they only occur when moisture is _____ before and ____ is _____ during

A

burn fuel s at the ground surface
shrubs, grasses, fallen branches, litter

may kill thin barked trees if it gets hot enough but won’t destroy mature forest

  • thins out
  • reduces combustible fuels

moderate before
wind moderate

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17
Q

forest with periodic surface fires are ____ flammable than those where light fuels have accumulated for years

why?

A

LESS

root system usually left alive

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18
Q

describe crown fires

A

build up enough head to ignite the canopy

more common in boreal forests than deciduous

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19
Q

what is a passive crown fires

A

burn along ground then spread into each tree
-flame length is enough to ignite the individual tree crowns but canopy fuels and/or rate of spread is insufficient to maintain fire in both surface and crowns

20
Q

describe ground fires

where are they most common?

A

burn subsurface organic fuels by moldering combustion
often ignited by surface fires

peatlands!!

21
Q

relationship between amount of peatland on the landscape and size of fires

A

more peatlands more fire

22
Q

define fire regime

A

characteristics of taiga fires

- pattern, freq, intensity

23
Q

what is the length of a fire cycle controlled by?

A

balance between precipitation and evapotranspiration

24
Q

___ ____ determines many of the plant dynamics of the boreal forest

A

fire cycle

25
Q

why can spring be a major fire season?

A

trees experience water stress (moisture loss bc warm temp, gain little from frozen soil)
low evapotranspirations

26
Q

how do pines protect themselves from fire?

A

thick bark

27
Q

which trees are more likely to crown? why?

A

conifer trees

depends on tree canopy architecture and understory vegetation

28
Q

which trees are least fire resistant? most fire resistant?

A

paper birch

jack pine

29
Q

what makes jack pine so fire resistant?

A

self pruning and self shedding
shedding dead branches reduces build of combustible fuels in canopy
self pruning low on trunk removes ladder branches

30
Q

means of post-fire reproduction

A

light, wind-dispersed seeds (birches, poplars)
serotinous cones (jack pine, black spruce)
stem sprouting/suckering (aspen/birch)

31
Q

define serotinous

why is it beneficial?

A

require heat of fire to open

beneficial time to reproduce bc of lack of other species
also, protects from rain, frost, bacteria, fungus, rodent teeth

32
Q

how are birch and aspen adapted to regenerate after a fire?

A

regenerate vegetatively by shoots and suckers arising along lateral roots
surface fires don’t get rid of roots, allowing this regeneration

33
Q

how do understory plants survive through fire?

A

survive as seeds buried in the soil for decades

  • germinate when canopy and leaf litter are removed by fire
  • sun warms soil
34
Q

example of a boreal plant species highly resistant to fire

A

cottongrass

35
Q

how does fire disturbance create a dynamic habitat mosaic?

A

elevates species diversity as diff species will be successful compared to regions where there hasn’t been fire

36
Q

why do invasive species pose a bigger threat to ecosystems?

ex?

A

no predators, diseases, or other natural forces to control their population
brown spruce longhorn beetle
gypsy moth

37
Q

why are boreal forest so susceptible to large-scale insect disturbance?

A 
low diversity (monoculture) makes it easy for them to spread
low productivity
38
Q

what triggers insect populations to increase?

A

sustained periods of warm weather
drought
(occurs over multiple years)

39
Q

what do climate models predict to occur when it comes to insect outbreaks?

A

increased temp could increase the risk of insect outbreaks

extreme winter weather is detrimental to insect outbreaks

40
Q

approx what percentage of annual boreal forest damage is weather/blowdown damage compared to harvested area and fire?

A

44%

41
Q

how does blowdown related to pathogens?

A

damage to tree stands increase the likelihood of pathogen outbreaks

42
Q

what are the top threats to coastal trees?

A

are susceptible to fire but wind and erosion are concerning

43
Q

how are boreal mammals adapted to disturbance?

A

utilizing edge habitats created by small disturbances

moose like disturbance

44
Q

how does disturbance affect biodiversity?

A

depends on scale and frequency

45
Q

how does low freq. disturbance affect biodiversity?

A

short lived species outcompeted by long lived

46
Q

how does high freq. disturbance affect biodiversity?

A

short lived species outcompete. no time to mature.

favours rapid growth rate, short life span, strong ability to colonize disturbed areas

Boreal Ecology (15 decks)

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