13.2 Disturbance and Recovery

Question 1

Healthy communities experience periodic

Answer 1

disturbances

Question 2

Following disturbance, plant communities change over time. This is called _________

Answer 2

ecological succession.

Question 3

Primary succession occurs in …

Answer 3

disturbed areas lacking soil.

Question 4

Secondary succession follows a disturbance that …

Answer 4

damages a community but leaves the soil intact

Question 5

how does succession promote biodiversity?

Answer 5

allows different types of plant
communities to exist in an area

Question 6

examples of disturbances caused by human activities

Answer 6

mining, deforestation, agriculture, or urbanization

Question 7

how do disturbances affect communities directly?

Answer 7

by killing organisms

Question 8

how do disturbances alter communities indirectly?

Answer 8

by changing the availability of abiotic resources such as shelter, nutrients, light, or water.

Question 9

Changes in the abiotic environment mean that …

Answer 9

the habitat may become suited to a different set of plant and animal species

Question 10

true or false: The effects of a disturbance are not always negative

Answer 10

true

Question 11

Despite the plant
and animal deaths caused by the disturbance, some organisms ____ in
the wake of the destruction

Answer 11

thrive

Question 12

examples of organisms that thrive in the wake of destruction

Answer 12

Moose and deer benefit from fire because it creates habitats where there is lots of new vegetation to browse.

Question 13

how can some seeds benefit from extreme heat?

Answer 13

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

Question 14

The type of disturbance is important because

Answer 14

disturbances change ecosystems in unique ways

Question 15

The severity of a disturbance
determines

Answer 15

the extent and intensity of destruction

Question 16

The frequency of disturbance determines

Answer 16

how much recovery time there is for the ecosystem

Question 17

A community that has already been altered by a disturbance may recover more ________ from a second event

Answer 17

slowly

Question 18

Some disturbances happen with
______________, allowing communities to adapt to and even ______ from disturbance.

Answer 18

predictable frequency; benefit

Question 19

Smaller-scale disturbances tend to _______

Answer 19

occur more frequently

Question 20

pioneer species

Answer 20

Early establishing species

Question 21

Pioneer species are often adapted to ___________ environments

Answer 21

high light or low nutrient

Question 22

example of pioneer species

Answer 22

Alder trees

Question 23

why do alders do well in disturbed areas
that have low-nutrient soils?

Answer 23

because nodules on their roots fix nitrogen, converting it into a form usable by plants

Question 24

As the pioneer plant species grow, they change the ____________ in the disturbed area.

Answer 24

biotic and abiotic conditions

Question 25

As the leaves shed by pioneer plants decompose, more nutrients _______ in the
soil.

Answer 25

accumulate

Question 26

Above ground, shoots of pioneer species create shade, ____________

Answer 26

moderating temperatures.

Question 27

the process of replacement of plants and other organisms that make up a community is called

Answer 27

ecological succession

Question 28

When a community arises in a lifeless area that has no soil, the change is called

Answer 28

primary succession

Question 29

examples of places with primary succession

Answer 29

Examples of such areas are new islands and landscapes created by erupting volcanoes or the bare rock left behind by a retreating glacier

Question 30

___________ are generally the first
organisms to appear during primary succession

Answer 30

Micro-organisms

Question 31

describe process of primary succession in an area

Answer 31

-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.

Question 32

Another type of primary succession

Answer 32

dune
succession

Question 33

first species to colonize the unstable sand in dune succession

Answer 33

grasses with long horizontal roots,
called rhizomes

Question 34

rhizomes

Answer 34

These grasses stabilize the sand dune, eventually allowing other species, such as sand cherry and dune willows, to colonize

Question 35

When a disturbance damages an existing community but leaves soil and
plants behind, the change in plant communities that follows is called

Answer 35

secondary succession

Question 36

Soil

Answer 36

living bank of plant seeds, fungal spores, and insect larvae that can speed the growth of a new community

Question 37

Forest areas that have been clear-cut, burned by a forest fire, or cleared for farming and then abandoned recover by

Answer 37

secondary succession

Question 38

process of secondary succession

Answer 38

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

Question 39

Of all species, ______ have had the greatest impact on the natural
environment

Answer 39

humans

Question 40

how can lime help an affected area?

Answer 40

Spreading lime reduced the soil acidity, which in turn reduced the toxic
effects of the soil metals and permitted plants to grow normally

Question 41

_____________ was considered to be a stable, self-perpetuating
community that existed in equilibrium with the area’s biotic and abiotic
environment

Answer 41

climax community

Question 42

ecologists now believe that the process of succession is often directed by ________, such as the season of the disturbance or
local rainfall patterns.

Answer 42

random events

Question 43

As a plant community changes following a disturbance, each successional
stage is defined by the __________ found in the ecosystem

Answer 43

dominant plants

Question 44

Within a given successional stage, small scale interactions and disturbances produce _______ of different habitat types.
This patchiness is important to maintaining ________

Answer 44

patches; biodiversity

Question 45

Describe an adaptation that reduces a plant species’ vulnerability to fire

Answer 45

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

Question 46

Describe how pioneer species change their
environment and improve the survival of
later-successional stage plants

Answer 46

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

Question 47

What factors, other than climate, determine the plant community in a particular region?

Answer 47

Local differences in topography,
soil composition, rainfall, and temperature influence plant community development.

Question 48

Explain how patchy habitats may increase
biodiversity

Answer 48

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.

Question 49

True or false: a healthy community is in a state of balance, with little change over time.

Answer 49

False

Healthy communities experience periodic disturbances.

Question 50

True or false:
Moderate levels of disturbance generally
act to reduce species diversity within a
community

Answer 50

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.

Question 51

True or false:
Small-scale disturbances can create patches of different habitats in a community.

Answer 51

true

small-scale interactions and disturbances produce patches of different habitat types.
This patchiness is important to maintaining biodiversity

Question 52

Describe the role of surviving plants in primary succession on Mount St. Helens.

Answer 52

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.

Question 53

Does a healthy community maintain a stable and constant composition of species despite disturbance? Explain.

Answer 53

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

Question 54

Are human-caused disturbances more likely to be damaging to communities than natural disturbances? Explain

Answer 54

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

Question 55

(a) What were the Sudbury Barrens?

Answer 55

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

Question 56

(b) What types of pollution led to the formation of the Barrens?

Answer 56

heavy metal pollution (sulphur dioxide and metal particle emissions from mining)

Question 57

(c) How were the Barrens remediated?

Answer 57

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

Question 58

Use a flow chart to explain why birch and spruce forests may alternate in Ontario woodlands

Answer 58

–>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

Question 59

first species to appear during secondary succession?

Answer 59

pioneer species