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

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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.


Perturbation

Perturbation

  • 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.


Forest blowdown

Forest blowdown


Succession

Succession

  • This process just described is called succession.

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


Successional change due to light tolerance

Successional Change Due TO Light Tolerance


Primary succession

Primary Succession

  • 3 types

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


Xerarch succession

Xerarch Succession


Primary succession1

Primary Succession

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

  • Glacial till – conifers in about 170 years.


Mesarch succession

Mesarch Succession


Primary succession2

Primary Succession

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


Hydrarch succesion

Hydrarch Succesion


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.


Gap phase regeneration1

Gap – Phase Regeneration


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 trees

Growth characteristics of intolerant and tolerant trees


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.


Response to low nitrogen availability

Response to Low Nitrogen Availability


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.


Forest stand map

Forest Stand Map


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.


Nitrogen cycle2

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.


The end

THE END


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