13.2 Disturbance and Recovery Flashcards
Healthy communities experience periodic
disturbances
Following disturbance, plant communities change over time. This is called _________
ecological succession.
Primary succession occurs in …
disturbed areas lacking soil.
Secondary succession follows a disturbance that …
damages a community but leaves the soil intact
how does succession promote biodiversity?
allows different types of plant
communities to exist in an area
examples of disturbances caused by human activities
mining, deforestation, agriculture, or urbanization
how do disturbances affect communities directly?
by killing organisms
how do disturbances alter communities indirectly?
by changing the availability of abiotic resources such as shelter, nutrients, light, or water.
Changes in the abiotic environment mean that …
the habitat may become suited to a different set of plant and animal species
true or false: The effects of a disturbance are not always negative
true
Despite the plant
and animal deaths caused by the disturbance, some organisms ____ in
the wake of the destruction
thrive
examples of organisms that thrive in the wake of destruction
Moose and deer benefit from fire because it creates habitats where there is lots of new vegetation to browse.
how can some seeds benefit from extreme heat?
Seeds of some species require exposure to the extremely high temperature of a forest
fire before they can germinate, or begin to grow.
For example, cones of jack pines are sealed shut by a gummy substance called resin.
-the cones cannot open to release seeds until the resin is scorched by fire
The type of disturbance is important because
disturbances change ecosystems in unique ways
The severity of a disturbance
determines
the extent and intensity of destruction
The frequency of disturbance determines
how much recovery time there is for the ecosystem
A community that has already been altered by a disturbance may recover more ________ from a second event
slowly
Some disturbances happen with
______________, allowing communities to adapt to and even ______ from disturbance.
predictable frequency; benefit
Smaller-scale disturbances tend to _______
occur more frequently
pioneer species
Early establishing species
Pioneer species are often adapted to ___________ environments
high light or low nutrient
example of pioneer species
Alder trees
why do alders do well in disturbed areas
that have low-nutrient soils?
because nodules on their roots fix nitrogen, converting it into a form usable by plants
As the pioneer plant species grow, they change the ____________ in the disturbed area.
biotic and abiotic conditions
As the leaves shed by pioneer plants decompose, more nutrients _______ in the
soil.
accumulate
Above ground, shoots of pioneer species create shade, ____________
moderating temperatures.
the process of replacement of plants and other organisms that make up a community is called
ecological succession
When a community arises in a lifeless area that has no soil, the change is called
primary succession
examples of places with primary succession
Examples of such areas are new islands and landscapes created by erupting volcanoes or the bare rock left behind by a retreating glacier
___________ are generally the first
organisms to appear during primary succession
Micro-organisms
describe process of primary succession in an area
-micro-organisms first to appear
-then lichens and mosses, which grow from
windblown spores, colonize the barren ground.
-soil develops from decomposed remains of early colonizers.
-then lichens and mosses may be overgrown by grasses and other herbaceous plants.
-seeds of these plants may have blown in from other areas or been carried in by animals.
-eventually, shrubs and trees become established.
Another type of primary succession
dune
succession
first species to colonize the unstable sand in dune succession
grasses with long horizontal roots,
called rhizomes
rhizomes
These grasses stabilize the sand dune, eventually allowing other species, such as sand cherry and dune willows, to colonize
When a disturbance damages an existing community but leaves soil and
plants behind, the change in plant communities that follows is called
secondary succession
Soil
living bank of plant seeds, fungal spores, and insect larvae that can speed the growth of a new community
Forest areas that have been clear-cut, burned by a forest fire, or cleared for farming and then abandoned recover by
secondary succession
process of secondary succession
Light-loving and fast-growing annual species, which grow, reproduce and
die within a year, are usually the pioneer species in the newly cleared area.
Within a few years, grasses and non-woody
perennial plants, which live for more than one year, become established.
Shrubs that are shade-tolerant and require
richer, moister soil may replace these first plants.
Eventually, trees may replace the shrubs
Of all species, ______ have had the greatest impact on the natural
environment
humans
how can lime help an affected area?
Spreading lime reduced the soil acidity, which in turn reduced the toxic
effects of the soil metals and permitted plants to grow normally
_____________ was considered to be a stable, self-perpetuating
community that existed in equilibrium with the area’s biotic and abiotic
environment
climax community
ecologists now believe that the process of succession is often directed by ________, such as the season of the disturbance or
local rainfall patterns.
random events
As a plant community changes following a disturbance, each successional
stage is defined by the __________ found in the ecosystem
dominant plants
Within a given successional stage, small scale interactions and disturbances produce _______ of different habitat types.
This patchiness is important to maintaining ________
patches; biodiversity
Describe an adaptation that reduces a plant species’ vulnerability to fire
Seeds of some species require exposure to the extremely high temperature of a forest
fire before they can germinate, or begin to grow.
For example, cones of jack pines are sealed shut by a gummy substance called resin.
The cones cannot open to release seeds until the resin is scorched by fire
Describe how pioneer species change their
environment and improve the survival of
later-successional stage plants
As the pioneer plant species grow, they change the biotic and abiotic conditions in the disturbed area.
The roots of these early plant colonizers
bind soil, allowing it to retain more moisture.
Many pioneer species help to add nitrogen to the soil that other species can use.
As the leaves shed by pioneer plants decompose, more nutrients accumulate in the soil.
This can improve the survival of later-successional stage plants
What factors, other than climate, determine the plant community in a particular region?
Local differences in topography,
soil composition, rainfall, and temperature influence plant community development.
Explain how patchy habitats may increase
biodiversity
Different plants and animals will be adapted to the different patch types.
Thus, an ecosystem is often made up of habitat patches, each with a different set of species.
True or false: a healthy community is in a state of balance, with little change over time.
False
Healthy communities experience periodic disturbances.
True or false:
Moderate levels of disturbance generally
act to reduce species diversity within a
community
false
Species develop new traits for tolerance or against disturbance, which causes diversity in the community. Therefore, a moderate level of disturbance is suitable for any healthy ecosystem, which contributes to species diversity.
True or false:
Small-scale disturbances can create patches of different habitats in a community.
true
small-scale interactions and disturbances produce patches of different habitat types.
This patchiness is important to maintaining biodiversity
Describe the role of surviving plants in primary succession on Mount St. Helens.
The roots of lupines house bacteria that fix nitrogen.
This helped to enrich the nutrient-poor mudflows formed by the eruption,
allowing other seeds to germinate and grow.
Does a healthy community maintain a stable and constant composition of species despite disturbance? Explain.
No, because enviroments are always changing due to disturbances, which changes the different species living there due to what they’re adapted to and can withstand
Are human-caused disturbances more likely to be damaging to communities than natural disturbances? Explain
Of all species, humans have had the greatest impact on the natural
environment.
When a forest or grassland is converted to farmland, a diverse community is replaced with crops of a single plant species reducing species diversity
Many human-caused disturbances are too vast or repeated too frequently to allow succession to proceed.
For example, land in the tropical rainforest that is cleared for forestry or agriculture will often not return to its natural state because the nutrients have been lost from
the ecosystem
(a) What were the Sudbury Barrens?
large scale example of human disturbance
Greater Sudbury has been degraded by many human activities, including forestry, mining, and nickel smelting.
The original vegetation was killed off by a combination of logging, acid deposition, and acidic soils with high levels of certain
metals.
The resulting Barrens around Sudbury were bleak, desolate, and lifeless areas
(b) What types of pollution led to the formation of the Barrens?
heavy metal pollution (sulphur dioxide and metal particle emissions from mining)
(c) How were the Barrens remediated?
The first step in restoration was to spread lime on the affected area.
-reduced the soil acidity, which in turn reduced the toxic effects of the soil metals and permitted plants to grow normally.
Grass and legume seeds were added next. -the successful grass species were tolerant
of heavy metal pollution.
The roots of legumes fix nitrogen.
These early steps mimicked the natural events of secondary succession, increasing
the nutrient availability and moisture of the soil
Use a flow chart to explain why birch and spruce forests may alternate in Ontario woodlands
–>spruce needles decompose slowly, releasing very few nutrients to
the soil –>
–>soil becomes nutrient-poor and spruce seedlings cannot grow–>
–>instead, birch seedlings invade spruce stands, changing the forests + animals that live there–>
–>many birch trees have root nodules full of bacteria that fix soil nitrogen–>
–>in addition, birch leaves decompose rapidly, releasing nutrients to forest soils–>
–>spruce seedlings grow well in the nutrient-rich soils created by the birch–>
–>as a result, the spruce reinvades among birch trees
first species to appear during secondary succession?
pioneer species
