People tend to think that forests are static but they are in fact constantly changing There are predictable changes

Transcription

1 Succession

2 People tend to think that forests are static but they are in fact constantly changing There are predictable changes Scientists can use these patterns To learn how forests grow To examine how human interference is changing ecosystems

3 Resources are limited Organisms are constantly competing for these resources Organisms adopt different ways to obtain resources Since forests and ecosystems change, organisms tactics have to change as well

4 Example of taking advantage of resources One species of trees grows quickly in sunlight Once fully grown, that tree shades is offspring A second species of trees prefer to grow in shady conditions Eventually it will outcompete other species One species becoming more dominant changes the composition of the ecosystem

5 Succession is the natural replacement of plant or animal species, or species associations, in an area over time

6 Succession During succession, biotic (living) and abiotic (nonliving) conditions change. Pioneer and intermediate communities alter conditions so much so that they promote the growth of new communities that eventually replace them.

7 During succession, two of the most notable changes are an increase in species diversity ecosystem stability

8 Types of Succession 1. Primary succession begins in areas where no soil is initially present Formation of new, unoccupied habitat Pioneer species= 1 st organisms to populate Ex. Lava flow, severe landslide, glacial recession 2. Secondary succession begins in areas where soil is already present Disturbance Ex. Fire, severe windthrow, logging

9 Characteristics of Pioneer Species Small in stature Light demanding/shade intolerant Rapid growth rates Early maturity High dispersal rates Symbiotic association to fix soil with nitrogen Examples: Bacteria, fungi, lichen

10 Characteristics of Non-Pioneer Climax species Species Large size and longlived Low individual growth rates Low population growth Shade tolerant Example: Douglas Fir

11 Primary Succession One of the most striking aspects of a newly formed lava flow is its lifeless nature. The process of colonization of such flows by plants and animals is called primary succession.

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14 The succession process relies heavily on adjacent ecosystems. A steady rain of organic material, seeds, and spores slowly accumulates in cracks and pockets along with tiny fragments of the new lava surface. Some pockets of this infant soil retain enough moisture to support scattered seedlings and a few hardy ferns and shrubs.

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16 Over time, the progeny of these colonizers, and additional species from nearby forests, form an open cover of vegetation, gradually changing the conditions to those more favorable to other organisms. The accumulation of fallen leaves, bark, and dead roots is converted by soil organisms, into a thin rich organic soil. A forest can develop in wet regions in less than 150 years.

17 Secondary Succession A long-term repair process that takes place after an ecosystem is destroyed by natural or human causes. Occurs more rapidly than primary succession because there is generally no need to form soil.

18 The soil left behind after a fire is very rich in nutrients and minerals. Secondary succession occurs quite rapidly following a fire. Some seeds even need the heat from the fire to germinate. Example Great Sequoias

19 Succession after a fire 1st year Horseweed dominant; crabgrass, pigweed 2nd year Asters dominant; crabgrass 3rd to 18th year Grass scrub community; bromomsedge grass, pines coming in during this stage 19th to 30th year Young pine forest 30th to 70th year Mature pine forest; Understory of young hardwoods 70th to 100th year Pine to hardwood transition 100th year plus Climax oakhickory forest

20 Forest Succession Stages Forbs -> Shrubs -> Young Forest -> Mature Forest -> Climax Forest Communities move through successional phases in response to changes in both their biotic and abiotic environment.

21 Climax Stage Stable end-stage Once a community becomes stable, mature, and little change in species, it is known as a climax community Community of plants that will grow and remain dominant in an area Biologists today feel that most natural ecosystems experience disturbance at a rate that makes a climax community unattainable

22 Biotic Factors influences Succession Insect epidemic High populations of deer - Overgrazing

23 Abiotic Factors Soil types species that grow on sandier, well drained soils Weather windstorms, drought, late spring frost Climate time and geography Moisture levels Fire many forest types have adapted to regular wildfires

24 Wetland Succession Interesting and important because wetlands play many roles in the natural world. They act as vessels for natural flood storage, as producers of diverse wildlife and as sinks for excess nitrogen and phosphorus which regulates water quality for both surface and groundwater.

25 Characterized mostly by structural changes in the plant community; however, changes in the rest of the habitat are dictated by changes in the plant base.

26 Wetlands being as areas of open water and slowly progress through series of algae and submerged plants, floating plants, hydrophilic grasses, shrubs, small tress and full wooded wetlands. The succession of wetlands in also characterized by changes in overall area as parts of the surrounding dry out

27 As areas dry out, adjacent species of terrestrial plants move in to occupy the place of now dead aquatic plants; as areas flood the terrestrial species die out and are replaces first with algae and then more complex aquatic plants.

28 Succession of a Pond