Chapter 6 Ecological Succession
Introduction
6-1 Ecological succession
6-2 Human-induced succession
6-3 Managing succession
Introduction
1. Ecological succession: natural processes continually change ecosystems.
2. Human-induced succession: people change ecosystem to serve their needs.
(1) Overgrazing and pasture degradation.
(2) Overfishing and replacement of valuable fish by trash fish.
(3) Severe forest fires when forests are protected from fires.
6-1 Ecological succession
1. Ecological succession: a single site has different biological communities, and
therefore different ecosystems, at different times.
2. Change from one biological community to another:
(1) Smaller species first coming; larger species come later.
(2) Species grows old and dies, and another species takes its place.
(3) Species create conditions that are more suitable for other species.
3.
4.
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(4) Destroyed by natural or human disturbance, and replaced by others.
Climax: the last stage of ecological succession; mature.
An example of ecological succession
(1) Western Japan: grass, shrub, oak, beech (fig. 6.1)
(2) Spatial variation with physical conditions and succession. (fig. 6.2)
Ecological succession as a complex system cycle
(1) Ecological succession is cyclic (fig. 6.3)
(2) Four stages: growth, equilibrium, dissolution, reorganization.
Interaction of positive and negative feedback in ecological succession
(1) Negative feedback: keep ecosystems the same (ecosystem homeostasis)
(2) Positive feedback: change from one stage to another
(3) Competition for sunlight and water (fig. 6.4)
7. Urban succession
(1) Social system: change from residential to commercial or industrial.
(2) Cities grow and decline as succession.
6-2 Human-induced succession
1. Pasture degradation due to overgrazing
(1) Nutritious grasses vs. un-nutritious grasses: balance (fig. 6.5)
(2) Grazing: nutritious grasses decline, and un-nutritious grasses grow
(3) Desertification: overgrazing, un-nutritious grasses decline (fig. 6.6)
2. Fisheries succession
(1) Fisheries succession: valuable fish declines; trash fish increases
(2) Changing into another aquatic ecosystem; OK vs. not OK (fig. 6.7)
(3) Moderate levels of fishing, grazing, logging (fig. 6.8)
6-3 Managing succession
1. Traditional forest management in Japan
(1) Satayama system: sustainable landscape management in Japan. 25-year-old
Oak rotation, tall perennial grass for house,
(2) Now using imported petroleum, fertilizers, oak replaced by beech
2. Forest fire protection
(1) Leaf litter: provides fuel for fires that are usually started by lightning.
(2) Mineral nutrients: P, K, from leaves after forest fire.
(3) Frequent fires are a negative feedback; however, fire protection is a positive
feedback (counterintuitive: opposite of what we expect) (fig. 6.9)
(4) Forest landscape with frequent natural fires is a mosaic (fig. 6.10)
(5) Controlled burning and selective logging to reduce fuel for a fire.
3. Ecological succession and agriculture
(1) Agricultural ecosystems: few species of plants and animals (immature)
(2) Slash-and-burn agriculture or shifting cultivation
(3) Abandoned patch is left in fallow for at least ten years
(4) Nutrient pump: deeply rooted trees bring plant nutrient to their leaves
(5) It is ecologically sustainable way, but not work for large population
(6) Agroforestry: mimics a natural forest ecosystem (fig. 6.11)