Lecture 5 - Disturbance Flashcards
Definition of disturbance
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
examples of natural causes of disturbance
fire flooding insect outbreaks volcanoes frostheave ocean currents
examples of human cause disturbance
agriculture urbanization logging/resource extraction mining road construction ecotourism
impacts of disturbance are influenced by what 3 general categories?
spatial factors
temporal factors
magnitude
describe the spatial factors influence disturbance
size
shape
connectivity
proximity to unaffected areas
describe the temporal factors influence disturbance
frequency
duration
time of year
what are the 3 most important natural disturbances in the boreal?
fire
insect infestations
severe weather
define succession
changes in equilibrium communities
replacement of one community to another
primary succession
vs
secondary succession
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
what is the most important cause of disturbance?
fire
what are two ways that fire is a primary agent of change in the boreal forest?
- releases nutrients
- reduces litter on forest floor and release nutrients that have been tied up in those materials - allows sunlight
- opens up canopy to sunlight –> stimulates regeneration from seeds and roots
- stimulates growth and reproduction
what causes fire?
lightning!
what percentage of total fires are made up by lightning?
why is it such a big factor?
35% of total fires
BUT
represents 85% of area burned
how will climate change impact lighting fires?
rising temperatures are expected to increase the number of lightning strikes
12% increase for each degree celsius
3 types of fires
surface fires -burn only on ground crown fires -burn only in canopy ground fires - burn along ground or underground
describe surface fires
they only occur when moisture is _____ before and ____ is _____ during
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
forest with periodic surface fires are ____ flammable than those where light fuels have accumulated for years
why?
LESS
root system usually left alive
describe crown fires
build up enough head to ignite the canopy
more common in boreal forests than deciduous
what is a passive crown fires
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
describe ground fires
where are they most common?
burn subsurface organic fuels by moldering combustion
often ignited by surface fires
peatlands!!
relationship between amount of peatland on the landscape and size of fires
more peatlands more fire
define fire regime
characteristics of taiga fires
- pattern, freq, intensity
what is the length of a fire cycle controlled by?
balance between precipitation and evapotranspiration
___ ____ determines many of the plant dynamics of the boreal forest
fire cycle
