Forest ecology and the forest ecosystem
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Forest Ecology and the Forest Ecosystem. Elements of Forestry. Kenneth Williams Fisheries Extension Specialist Langston University Aquaculture Extension Program. Forest Community Development. Long developmental period 35 years in the Southeastern U.S. 100 years in the Rocky Mountains.

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Forest ecology and the forest ecosystem

Forest Ecology and the Forest Ecosystem

Elements of Forestry

Kenneth Williams

Fisheries Extension Specialist

Langston University Aquaculture Extension Program

Forest community development
Forest Community Development

  • Long developmental period

  • 35 years in the Southeastern U.S.

  • 100 years in the Rocky Mountains

Forest community development1
Forest Community Development

  • Succession – ecological development from pioneer species to climax community.

  • Silviculture affects succession, either speeding it forward, maintaining the current situation or setting it back to an earlier stage of development.

Forest community development2
Forest Community Development

  • Plantings of climax species can speed succession.

  • An improvement cut can speed or set back succession.

  • Selective harvest can maintain a mature stand’s structure.

Tolerance competition and succession
Tolerance, Competition And Succession

  • What determines distribution of tree species?

Shade tolerance
Shade Tolerance

  • Tolerant species - grow comparatively well when little light is available but does not show large growth increases with increasing light level.

  • Intolerant species – Opposite. Poor growth at low levels of light. But faster growth than tolerant species at near full sun exposure.

Light tolerance
Light Tolerance

  • 2-5% of light striking the canopy reaches forest floor.

  • Intolerant or intermediate species will not have a positive growth rate because light level is not above compensation point for the species.

  • Compensation point – amount of light necessary to produce a net energy gain.

Light tolerance1
Light Tolerance

  • Only tolerant species can grow in dense shade.

  • Unless a perturbation occurs, tolerant species will dominate forest.

  • Perturbations – fire, tornado, winds, disease etc.


  • Opens up forest floor to light.

  • Intolerant species grow quickly. (generally thin crowns, so light passes through)

  • Intermediate and tolerant species grow beneath their canopy. (stratified canopy).

  • Eventually tolerant species grow taller and intolerant and intermediate species die. Tolerant species again assume dominant position.


  • This process just described is called succession.

  • Succession - An orderly replacement of species through time in a given location.

Primary succession
Primary Succession

  • 3 types

  • Xerarch – dry sites ex. Bare rock to juniper shrub. Tied to soil development.

Primary succession1
Primary Succession

  • Mesarch – moist, cool climate. Parent material, glacial.

  • Glacial till – conifers in about 170 years.

Primary succession2
Primary Succession

  • Hydrarch – cold, free standing water. Ex. A small pond or lake in the Great Lakes region.

Secondary succession
Secondary Succession

  • Setting back succession to an earlier time. Not necessarily to bare earth.

  • Ex. Clearing forest for farm land.

  • Old-field succession – farm field - grasses to trees. Takes longer than primary succession to reach climax.

  • Most forestry practices deal with some kind of secondary succession.

Gap phase regeneration
Gap – Phase Regeneration

  • Small-scale disturbance in the forest canopy. Ex. A tree falls and dies. Or a small area is logged.

  • Light levels not as high as out in the open but higher than under the forest canopy.

  • A form of secondary succession.

  • Intermediate tolerance trees often begin to grow.

  • Because this occurs – intermediate trees will be found in climax forest.

Seed dispersal strategies
Seed Dispersal Strategies

  • How intolerant seeds can sprout when forest canopy opens up.

  • Fugitive strategy – transported by wind or animals.

  • Buried-seed strategy – heavy seeds buried in forest floor can remain alive but dormant for 100 years or more. Ex. Pin cherry or blackberry.

Seed dispersal strategies1
Seed Dispersal Strategies

  • Tolerant species tend to have fairly heavy seeds that do not fall far from the parent tree.

  • Intermediate trees have seeds that are intermediate in weight and can be moved a bit by the wind but not as much as intolerant species.

Growth characteristics of intolerant and tolerant trees1
Growth characteristics of intolerant and tolerant trees

  • Different characteristics make different species attractive as crop trees.

  • Fast growth, high yield, early harvest and relatively large size are usually characteristics needed in a crop tree.

  • Ex. Loblolly pine, red pine and aspen. Mostly intolerant species.

Competition for resources
Competition for Resources

  • Species response to low nitrogen availability is much like that of light. Tolerant, intermediate and intolerant.

Competition for resources1
Competition for Resources

  • Niche – set of environmental conditions in which the species can survive, compete and reproduce. A multi-dimensional concept.

  • Includes: nutrient requirements, light, temperature tolerance, water requirements, disease and insect resistance etc.

Competition for resources2
Competition for Resources

  • Allelopathy – some plants excrete chemicals that inhibit germination, growth or metabolism of other plants.

  • Ex. Black walnut. Substance - juglone.

  • Allelopathy widespread in forest communities. One reason for associations of certain trees in forests ex. Yellow birch can grow with beech trees but not sugar maple.

  • Used in gardening.

Competition for resources3
Competition for Resources

  • Difficult to separate allelopathic effects from competitive interactions and species – site interactions.

Ecosystem studies and forest management
Ecosystem Studies And Forest Management

  • Ecosystem studies are integrative. Require expertise from many disciplines.

  • Ex. Soil science, hydrology, plant science, forestry, geology, fish and wildlife and microbiology.

What is an ecosystem
What Is An Ecosystem?

  • Watershed – unit of land whose rainfall all flows into a single stream.

  • Stand – any area of forest vegetation whose site conditions, past history and current species composition are sufficiently uniform to be managed as a unit.

Nitrogen cycle
Nitrogen Cycle

  • Rainfall hits leaves and takes up some nitrogen. This water is called throughfall.

  • Much of the nitrogen taken up is returned the same year to the forest floor as litter.

  • The litter is decomposed and made available to the plant in a process called mineralization.

Nitrogen cycle1
Nitrogen Cycle

  • Total available nitrogen at any one time is small. Most tied up in plants and litter.

  • Nitrogen fixation and denitrification by bacteria also increase complexity of the nitrogen cycle.

Ecosystem computer models
Ecosystem Computer Models

  • A model is a summary of everything known about a particular ecosystem. Using data inputs, the model tries to predict the most likely outcome of various forest manipulations.

Model construction
Model Construction

  • Model Structure – general outline of data and information available.

  • Parameterization – the specific data entered for a particular forest.

  • Validation – test accuracy. Use on previously conducted experiment.

  • Prediction – model used to predict results of experiments not yet carried out. Or potential forestry practices.

Model construction1
Model Construction

  • Validation is very important. If model cannot predict results of past experiments, it can not be relied on to predict results of future management practices.