Ecological Succession

Page 1

LU 5

- ECOLOGICAL SUCCESSION

Definition

= observed process of change in the species structure of an ecological

community over time.

Such

as ? = forest could once be a lake like 1000 years ago. Mosses, shrubs, and

small trees cover the concrete of a demolished building.

1.

When ponds age, they fill with sendiments &

organic matter. So they become shallower, and smaller ponds. Then they become

wetlands. And lastly, they become solid ground.

Where

does succession start ? = Bare area (rock & water) / disturbled area.

Factors

=

1.

Climate causes. = Some plants can’t adjust to

long variations of the climate. Diff climatic changes the vegetation like wind

(eliminate the previous vegetation), drought (drying & killing weaker

species) & snow ( killing previous vegetation)

2.

Physiographic = Erosion (by water, wind &

gravity), deposition of soil, emergence of barren land surfaces.

3.

Biotic = Human activities destroy the natural

vegetation. Animals overgrazing.

Succession

can be initiated by

1.

Formation of new unoccupied habitat = a lava

flow or a severe landslide = primary succession

2.

Disturbance of an existing community = forest

fire, windstop with severe windthrow, human activites like logging and

agricultural stuff = secondary succession

How

does it occur ?

-

biotic comm. Are dynamic in nature and they can

change over time.

-

In any community, some species may becomes less

abundant over some time. Or they can vanish. Similarly, some can become more

abundant, or new speceis can invade into the community from other adjacent

ecosystem.

-

This change over time in whatever species that

is living in an ecosystem = ecological sucession.

ES =

process of comm. Development, thru series of intermediate successional stages

leading to ‘climax’ community. Both abiotic & biotic are involved.

2

types = primary & secondary.

Primary

1.

Development starts on an area that hasn’t been

occupied yet by a previous community.

2.

Examples = newly exposed rock / sand surface, or

newly formed volcanic surfaces like lava flow, a newly exposed glacial tills,

and newly formed lake.

3.

Steps = bacteria/lichens arrive, they don’t need

soil to survive, they are called pioneer species. When they die, they decompose

so they add small amount of organic matter to the rock tomake soil. Then simple

plants come like mosses and fers. They can grow in the new soil. They die, they

add more organic materia. Then the soil layer thickens, where grasses,

wildflower & other plants take over. Insects, small birds and mammals will

start to move in. Whatever it was the bare rock, now can support a variety of

life.

4.

Bare rock --. Lichens --> small annual plants

and lichens --> grasses & perennials --> intermediate species =

grasses, shrubs, and shade intorerant trees like pines ---> climax community

= Shade tolerant trees like oak & hickory.

Secondary

succession

1.

starts in a place that already have soil. Which

was once a home to living organisms.

2.

It occurs on a previously occupied sites after

disturbance

3.

Disturbance = process that results in the

removal (partial/complete) of the existing vegetation.

4.

DISTURBED = removed by animals or humans or

natural phenomena = abandoned agricultural lands / cut over forest = forest

fires set by lightning or human activity = avalanches / landslides / volcanic

eruptions / earthquake/ floods/ wind storm/ prolonged severe drought.

5.

Usually more rapid because the colonizing area

is already rich in leftover soil. Organic matter & seeds of the previous

vegetation.

Fire

--> nothing ---> annual plants(1/2 years) --> grasses & perennials(3/4

years) --> grasses shrubs pines young oak & hickory(5-150 years) -->

mature oak & hickory forest. (150+ years)

Hydrosere

succession = plant succession which occurs in an area of freshwater.

Photoplankton

--> rooted submerged hydrophytes --> free floating plants --> reed

swamp stage --> sedge marsh / meadow stage --> woodland stage -->

climax forest.

Open

freshewater, deep water can’t support rooted plants. Because not enuf light for

photosynthesis. But there will be microorganisms & plankton floating. Over

time, sendiments will enter the lake via streams / rainwater draining it form

the land. Waterlilies can be established. It’s rooted but has floating leaves.

Pond becomes shallower, swamp appears. Water is too shallow for fully submerged

plants, so emergent plants like yellow iris & reedmace appears. They can

grow partly in and out of water. Then marsh appear, the floor will rise above

water level. Swamp plants die & can’t adapt. Then alder/willow appear. The

soil is wet but unlike marsh and swamp, they aren’t waterlogged and anaerobic.

Willow will dominate the ground & support a lot of invertebrates. Climax

woodland occurs = trees like oak ash and beech. They grow slowly, and will

dominate the area in time.

Primary

= site unoccupied. Region has no plant life. Lacks soil & organic matter.

Challenging for pioneer community. Long times, over 1000 years.

Secondary

= previously occupied after disturbance, region has plant life. Like seens/

underground stems. Region retains soil & organic matter. Plants that

survived can easily grow to form a pioneer community. Short time = 50-200

years.

Seasonal

& cyclic succession = not like secondary succession. Aren’t dependant on

disturbance but arise from fluctuating species interaction / recurring event.

Climax

community = final/stable community. Self-perpetuating & in equilibrium with

abiotic. No net annual accumulation of oranic matter in climax community

mostly. Annual production & use of energy is balanced.

Characteristics

of climax community

1.

can tolerate environmental conditions

2.

wide diversity of species, well drained spatial

structure, & complex food chains.

3.

Climax ecosystem is balanced. = there is

equilibrium between gross primary production & total respiration, between

energy used from sunlight & energy released by decomposition, between

uptake of nutrient from the soil & the return of nutrient by litter fall to

the soil.

4.

Species composition maintains equilibrium. Indiv

is replaced by others of the same species.

5.

It is an index of the climate of the area. The

life or growth forms indicate the climatic type.