lecture 8: ecological succession and community development huang he phone: 18972127775 qq:105367750...
TRANSCRIPT
Lecture 8: Ecological Succession and Community
Development
Lecture 8: Ecological Succession and Community
Development
Huang He
Phone: 18972127775 QQ:105367750 E-mail: [email protected]
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August 27, 1883
Island of Krakatau 喀拉喀托火山
Volcano erupted followed by tsunamis 海啸
Catastrophe 大灾难 , 大祸 natural lab
Ecologists studied the colonization of species
Source islands: Sumatra and Java (40km from Krakatau)
Sea-dispersal arrived first (10 of 24 by 1886)Others, wind-dispersed grasses and ferns and moved away from beachThen wind-d trees, birds and bats arrived …
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Plants dispersed by physical forces are the first to arrive in primary succession原生演替
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College of Chemistry and Environmental Engineering Huang He
Outline
8.1 The concept of the sere includes all the stages of successional change
8.2 Succession ensures as colonists alter environmental conditions
8.3 Succession becomes self-limiting as it approaches the climax
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Cleaning of oak-hornbeam forest
7 years after 15 years after
30 years after95 years after 150 years after
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College of Chemistry and Environmental Engineering Huang He
8.1 Community structure changes through time
Successional changes over 30 years in a western Pennsylvania field.
Cropland or Grazed grassland grasses, goldenrod, weedy herbaceous plants shrubs (blackberry, hawthorn 山楂 ) fire cherry, pine, aspen forest of maple, oak, cherry or pine.
Grazed grassland in 1942aspen and maple in 1972
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College of Chemistry and Environmental Engineering Huang He
Succession 【生】演替 ; 系列 ; 世系 , 系统
Definition: The process of gradual and (seemingly) directional change in the structural of the community through time (from open field to forest)
Temporal change in community structure
Sere 演替系列 (from the word series): The sequence of communities from grass to shrub to forest
Seral stage: each of the changes is a seral stage, is a point of continuum of vegetation through time,can be short or long (1 or 2 yrs to several decades)
Climax community: ultimate association of species achieved
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College of Chemistry and Environmental Engineering Huang He
Species dominance change along time
William Sousa
Process of succession in a rocky intertidal algal community in southern California (by W. Sousa)
Use concrete blocks for algae to colonize
Panel b shows succession
Early successional species (pioneer species):
High growth rate, small size, high degree of dispersal, high rates of population growth
Late successional species:
Low rate of dispersal, slower growth rate, larger and live longer (competition?).
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College of Chemistry and Environmental Engineering Huang He
Species dominance change along time
Hubbard Brook Experimental Forest, New Hampshire
Process of succession after forest clearing
Prior to forest clearing, beech and sugar maple seedling dominate understory
Following clearing, pin cherry, yellow birch etc. will replace. After many years, sugar maple and beech will dominate.
Primary succession (example before, a site unoccupied by a community) and
secondary succession (this example, occurs on previous occupied site after disturbance, remove part or all vegetation)23/4/22 10
Old field on the Piedmont of North Carolina. Abandoned agricultural fields undergo a series of successional changes. (shrubs start to replace annual plants)
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College of Chemistry and Environmental Engineering Huang He
Primary succession occurs on newly exposed substratesPrimary succession begins on sites that never have supported a community, such as rock outcrops and cliffs, sand dunes, and newly exposed glacial till.
Primary succession on a coastal sand dune colonized by beach grass
Later on, shrub, then trees (pines and oak if they can survive)23/4/22 12
Primary succession occurs on newly Primary succession occurs on newly exposed substratesexposed substrates
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Glacier Bay fjord complex in southeastern Alaska. Ice retreats, primary succession occurs
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Secondary succession occurs after disturbancesTerrestrial environment:
Oldfield succession in the Piedmont region of North Carolina by Dwight Billings in the late 1930s
Abandoned farmland
1st yr: crabgrass, horseweed
2nd yr: horseweed, white aster and ragweed
3rd yr: broomsedge, pine seedling
5-10th yr pine
Later oak and ash
Decline in pine and increase in hardwood (oak and hickory)23/4/22 15
Plant life history influence old-field succession
Tolerance and inhibition interact with life history to shape details of the species sequence during succession. Oosting and Keever, Duke University, 1950s, old field study, Piedmont, NC23/4/22 16
The climax communityFriderick Clements (1916, 1936): Monoclimax hypothesis
view community as a highly integrated superorganism, the process of succession represents gradual and progressive development of community to ultimate or climax stage (similar as development of an individual organism)
Clements’ climax community:
Community is like an organism, it arises, grows, matures, and dies.
Seres are different stage of development, ultimately lead to similar climax community
Fourteen climaxes:
2 grassland: prairie and tundra
3 scrub: sagebrush, desert scrub and chaparral
9 forest: pine-juiniper woodland to beeh-oak forest
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The climax communityNew views consider climax communities represent a continuum of vegetation types
Communities were ordered along a continuum index
Continnum index: scale of an environmental gradient based on the changes in physical characteristics or community composition along the gradient
Stages in the sere will lead to sugar maple climax community, but so-called climax vegetation actually represents a continuum of forest types
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8.2 Succession ensures as colonists alter environmental conditions
Two factors determines a species’s present in a sere:1.How readily it invades a newly formed or disturbed habitat2. Its response to environment over the course of succession
F. Egler (1954):Initial floristic compositionSuccession at any site depends on which species gets there first. No species is competitively superior to another. Once the original dies, the site becomes available to others.
Joesph Connell and Ralph Slatyer (1977): three models (facilitation model, inhibition model, and tolerance model)
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Mechanisms of Succession
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Alder facilitates succession by adding nitrogen to soils
Alder trees harbor nitrogen-fixing bacteria in their roots, providing nutrient to soils, facilitate the establishes of nitrogen-limited plants such as spruce, which will replace alder later.
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Facilitation, inhibition, and invasive speciesFacilitation, inhibition, and invasive species
Mycorrhizae fungi and plants: mutualistic symbiosisFungi can facilitate or inhibit plant growth (positive and negative)Effects are larger in home-home than home-foreign23/4/22 22
The differing adaptations of early and late The differing adaptations of early and late successional speciessuccessional species
Early-stage species and later inhabitants tend to have different strategies of growth and reproduction.
Early-arriving species:High dispersal ability.(dandelion, milkweed)
Climax species: large size, slow growth, but shade-tolerance as seedling (oak, maple)
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The survival of tree seedlings in shade is directly related to seed weight
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8.3 Succession becomes self-limiting as it approaches the climax
Succession continues until the addition of new species to the sere and the exclusion of established species no longer change the environment of the developing community.
The progression from small to large growth form modifies the conditions of light, temperature, moisture and soil nutrients.
Conditions change slowly after the vegetations achieves the largest growth form that the environment can support.
Final dimensions of a climax community are limited by climate independently of events during succession.
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Succession becomes self-limiting as it approaches the climax
Time required for succession from a new or disturbed habitat to a climax community
Depends on nature of climax and initial quality of habitat
Mature oak-hickory climax forest from old field in North Carolina: 150 yrsClimax stage of grasslands in western North America: 20-40 yearsHumid tropics, reach climax within 100 years from clear cut, but may take a few more centuries to achieves a fully mature structure and species composition.
Sand dune beech-maple climax, up to 1,000 years
Climate change, hunting, fire, and logging, disappearance of keystone consumers (wolf, passenger pigeon) and trees (chestnuts, eastern hemlock)
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Climax communities under extreme environmental conditions
Fire is an important feature of many climax communities, favoring fire-resistant species and excluding species that would otherwise dominate.
Longleaf pine after a fire
Seedling may be badly burned, but the growing shoot is protected by the long, dense needles.
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Grazing pressure also modify a climax community
Grassland can be turned into shrubland by intense grazing
Herbivivores may kill or severely damage perennial grasses and allow shrubs and cacti that are unsuitable for forage to invade.
Selective grazing
Some species prefer to feed on areas previously grazed by others. Both zebras and Thompson’s gazelles feed on Serengeti ecosystem of east Africa, but eating different plants.
In North America, cattle grazing may lead to invasion by alien cheatgrass, which promote fire.
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Transient and cyclic climaxes
Succession is a series of changes leading to a stable climax, whose character is determined by local environment. Once established, a beech-maple forest perpetuates itself, and its general appearance changes little despite constant replacement of individuals within the community. Transient climaxes: such
as communities in seasonal ponds – small bodies of water than either dry up in summer, or freeze solid in winter.
The extreme seasonal changes regularly destroy the communities that become established in the ponds each year.
On African savannas, carcasses of large mammals are devoured by a succession of vultures including: large, aggressive species smaller species that glen smaller bits of meat from bone species that cracks open bone to feed on marrow.
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Cyclic climax:
Suppose, for example, species A can only germinate under species B, B only under C, and C only under A. The relationships create a regular cycle of species dominance in the order of A, C, B, A, C, B, A, …, in which the length of each stage is determined by the life span of the dominant species.
Cyclic succession is usually driven by stressful environmental conditions.
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When high winds damage heaths and other types of vegetation in northern Scotland, shredded foliage and broken twigs create openings for further damage, and soon a wide swath is opened in the vegetation. Regeneration occurs on the protected side of damaged area while wind damage further encroaches on exposed vegetation.
Temporal: wind damage and regenerate, cycling
Spatial: mosaic patches
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8.4 The concept of community revisited
Two views of community: holistic (organismal) view and individualistic view
Clements’s Organismal community is a spatial concept: variety of plant and animal species interacting and influencing the overall structure
Gleason’s Continuum view is a population concept, focusing on the response of the component species to the underlying features of the environment.
An example (demonstrate two views)
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Topographic distribution of forest communities in the Great Smoky Mountains National Park (west-facing) OH: red- oak-pignut hickory
OCH: chestnut oak-chestnut heath OCF: chestnut oak-chestnut forest ROC: red oak-chestnut H: Helmock forest; P: pine; F: Frazir fir; SF: spruce-fir; S: Red spruce; GB: grassy balds HB:Heath balds
An example of forest zonation
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Patterns of co-occurrence for 4 plant species on a landscape along a gradient of altitude23/4/22 34
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