Transcript chap6ecology - Langston University Research and Extension

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
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 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

What determines distribution of tree
species?
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

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 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

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
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
Primary Succession

3 types
 Xerarch – dry sites ex. Bare rock to juniper
shrub. Tied to soil development.
Xerarch Succession
Primary Succession
Mesarch – moist, cool climate. Parent
material, glacial.
 Glacial till – conifers in about 170 years.

Mesarch Succession
Primary Succession

Hydrarch – cold, free standing water. Ex. A
small pond or lake in the Great Lakes
region.
Hydrarch Succesion
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

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
Regeneration
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 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

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

Species response to low nitrogen
availability is much like that of light.
Tolerant, intermediate and intolerant.
Response to Low Nitrogen
Availability
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 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 Resources

Difficult to separate allelopathic effects
from competitive interactions and species –
site interactions.
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?
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
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 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
Cycle
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 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 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