Forest Ecology and the Forest Ecology and the Forest EcosystemForest Ecosystem

Kenneth WilliamsFisheries Extension Specialist Langston University Aquaculture Extension Program

Elements of Forestry

Forest Community DevelopmentForest Community Development

Long developmental period35 years in the Southeastern U.S.100 years in the Rocky Mountains

Forest Community DevelopmentForest 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 DevelopmentForest 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 Tolerance, Competition And SuccessionSuccession

What determines distribution of tree species?

Shade ToleranceShade 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 ToleranceLight 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 ToleranceLight Tolerance

Only tolerant species can grow in dense shade.

Unless a perturbation occurs, tolerant species will dominate forest.

Perturbations – fire, tornado, winds, disease etc.

PerturbationPerturbationOpens 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 blowdownForest blowdown

SuccessionSuccession

This process just described is called succession.

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

Successional Successional Change Due TO Change Due TO Light ToleranceLight Tolerance

Primary SuccessionPrimary Succession

3 typesXerarch – dry sites ex. Bare rock to juniper

shrub. Tied to soil development.

Xerarch SuccessionXerarch Succession

Primary SuccessionPrimary Succession

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

Glacial till – conifers in about 170 years.

Mesarch SuccessionMesarch Succession

Primary SuccessionPrimary Succession

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

Hydrarch SuccesionHydrarch Succesion

Secondary SuccessionSecondary SuccessionSetting 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 RegenerationGap – Phase RegenerationSmall-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 Gap – Phase RegenerationRegeneration

Seed Dispersal StrategiesSeed 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 StrategiesSeed 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 Growth characteristics of intolerant and tolerant treesintolerant and tolerant trees

Growth characteristics of Growth characteristics of intolerant and tolerant treesintolerant 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 ResourcesCompetition for Resources

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

Response to Low Nitrogen Response to Low Nitrogen AvailabilityAvailability

Competition for ResourcesCompetition 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 ResourcesCompetition 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 ResourcesCompetition for Resources

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

Ecosystem Studies And Forest Ecosystem Studies And Forest ManagementManagement

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 Forest Stand Stand MapMap

Nitrogen CycleNitrogen 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 CycleNitrogen 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 Nitrogen CycleCycle

Ecosystem Computer ModelsEcosystem 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 ConstructionModel 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 ConstructionModel 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 ENDTHE END