Module 2
Forest Ecosystem
structure and function
O.T. Helgerson WSUCE 10/02
FOREST ECOLOGY
Just how does it pertain to forest
stewardship planning…
Forest ecology effects:
All Resource Categories
• Forest health
• T&E species,
cultural resources
• Timber and wood
products
• Esthetics &
recreation
• Soils
• Agro-forestry &
• Water
spl.
forest
prod.
• Fish & wildlife
Ecosystems consist of…
• Communities of animate (living) things:
plants, animals, microbes, et al.
• Inanimate stuff (rocks, soils, gasses,
chemicals)
• Exchange matter and energy
– Within the system
– Between systems
• Systems interact and are interdependent
Another example ecosystem….
Diesel
+ O2 in
Exhaust
out
Animate
object in cab
Trees
in
External
interactions &
interdependencies
Internal interacting &
interdependent systems
Logs
out
Ecosystems vary in scale…. Depends on what we’re
interested in….
Harvest setting or stand
cull
log
Douglas-fir
needle
Ecosystems on a landscape scale…
watersheds, timbersheds, spotted owl sma’s
Photo: Oregon State University College of Forestry
Until interplanetary travel becomes
cost effective…..
Photo: Oregon State University College of Forestry
Ecosystems have:
Structure & Function
• Structure:
• Function
– How is it put together?
– What does it do
Different structures…
Different functions….
Ecosystem structure
(sizes and arrangement of
plants, animals, dead stuff
et al.)
Op.
Env.
Ecosystem function
(the operational
environment, exchange
of matter and energy)
operational environment:
the physical environment around a living
organism; governs how ecosystems interact
and function
light
heat
mechanical
chemical
Operational environment
affects everything
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Growth
Disease
Insects
Reforestation
Distribution of plant and animal species
Operational environment
• BIG drivers
–
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climate
elevation, slope, aspect
geology & soils
land conversion
fire policy
floods
biota
• Not so big drivers
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timber harvest
silviculture
land conversion
microclimate
landslides
floods
plants & animals
which leads to…
why are plant species found
where they are found?
Answer: its evolved adaptation to its
surrounding operational environment
SO, HOW DO I KNOW
WHAT MY TREES ARE?
and….
Ecological communities
• Plants and animals occurring together in a
coherent group because of their adaptations
to each other and the surrounding
environment
• (Communities become ecosystems when we include
processes behind interaction and interdependency)
Physiographic and geologic provinces of
Washington (Franklin and Dyrness 1973)
BLUE
MOUNTAINS
COAST
RANGE
BLUE
MOUNTAINS
Temperature and
water availability
are the two big
drivers in
determining forest
type
Fire is important…
Geology, e.g.
serpentine soils, may
be locally important
Figure: USDA forest Service
How does your forest type
affect your forest management
goals?
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Let’s take a closer look at some
natural forces…..
Natural forces (disturbances)
modifying the operational
environment…
• wind throw
• root disease
• global climate
change
• volcanoes
• landslides
• floods
• and…
Fire, natural and human caused, is a major force
driving plant succession in North American
forests…
Some trees and shrubs are adapted to fire, while
others are not
Photo courtesy Bureau of Land Management
II
F
Pre-settlement fire intensity and frequency
Adapted from USDA Forest Service, Dr. James Agee UW COF
Before fire suppression, east-side fires were
typically low intensity and fairly frequent
ground fires, leading to open stands of
ponderosa pine and larch over much of the
landscape.
Photo courtesy Bureau of Land Management
West-side fires tended to be infrequent,
catastrophic stand replacing fires….
Due to fire suppression and fuels buildups, atypical
catastrophic fires now occur on the east-side….
Timber harvesting is one way to reduce fuel loads
in east-side stands to less damaging levels.
Photo courtesy Bureau of Land Management
Due to air quality regulations and loss of trained
agency personnel, prescribed fire, as shown here, is
used less frequently.
Forest succession
community changes because
plants change the operational
environment
See: Forest Ecology in Washington
handout
Forest succession
• Primary succession
follows big
disturbance
• Early seral plant
species
• Best in full sunlight
conditions
• Secondary succession
after initial plant
community
• Late seral species
• Best tolerate shade and
other understory
conditions
See: Forest Ecology in Washington
handout
The intense shade under this
salmon berry seems to prevent
even shade tolerant species
from getting established here
without some kind of
disturbance
Shade is less intense under
red alder, favoring slow
natural establishment of
western red cedar and
western hemlock over
Douglas-fir
Forest succession
• the changed
operational
environment may
help perpetuate
the existing plant
community, OR,
set the stage for
the next
community….
Shasta red
fir seedling
Succession in an even-aged
Douglas-fir forest
Where is your forest headed?
Mostly shade
intolerant plant
species
Figure from Washington State University Cooperative Extension
Conversion to shade
tolerant tree species
Succession may have many
end points
• 45-year-old
Douglas-fir stand
(Idaho)
• Root disease and
bark beetles
affected outcome
• Susan K Hagle,
USDA Forest
Service, Western
Forester, 2002
How does succession affect your
forest management goals?
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What about human induced
ecosystem changes?
Harvesting affects the operational environment.
Here…greatly increased light, heat, water, chemical turnover;
soil compaction?, mycorrhizal effects?
forest succession is
restarted…
Thinning effects: less increase in light, heat,
water, nutrient turnover;
mechanical damage to leave trees?, soil
compaction?
forest succession may be accelerated…
Productivity…
what makes the whole works run?
PHOTOSYNTHESIS
100
PHOTOSYNTH
%
ESIS
2.46%
2%
Foliage
Boles & branches
Below ground
LOW SITE
HIGH SITE
Photosynthate allocation and site quality
(Perry 1994)
HEAT
Leaf Area Index
An acre of highly
productive forest may
have 12 or more acres
of leaves over it;
where’s there most available water and good
temperatures, there’s greatest productivity
Trophic levels
T1 Producers
T2 Herbivores
T3 Primary Carnivores
T4 Secondary Carnivores
T5 Decomposers
Energy flows are like log processing: there’s an
attempt to maintain maximum value at every
step, or ecologically, nature tends to fill all
niches with communities
the T1 level
The environmental drivers determining species location
also determine productivity. Soils management is very
important.
Nice little T2 Herbivores at work…
The western spruce budworm is a serious
pest on east-side forests overstocked with
true firs and Douglas-fir
Photo: Natural Resources Canada, Canadian Forest Service,
http://www.pfc.cfs.nrcan.gc.ca/entomology/defoliators/budworms/west_spruce_e.html 20041119
Decomposers (T5) are essential within a forest
ecosystem for nutrient cycling…
Decomposers include larger insects, and a fantastic variety
of microscopic insects, bacteria, fungi and actinomycetes
Photo: Dr. A. Moldenke, Oregon State University
Photo: Dr. A. Moldenke, Oregon State University
Mycorrhizae:
Symbiotic fungi that infect tree roots
• Mutual benefits
– Greatly expanded root
network (increased
water, nutrients)
– Essential hormones
– Pathogen protection
– Attracts microscopic
insects for bug poop
near roots
– Fungi get food from
tree
White stuff
is
mycorrhizal
hyphae
Photo: Dr. R. Molina, Oregon State University
What happens within and around
a primary root…?
Fungi infect
this blue layer
of cells
Water, dissolved
nutrients and
hormones carried
up to needles in
xylem cells
(wood)
Photo: Dr. R. Molina,
Oregon State University
Fungal hyphae
connect root
with water and
nutrients on
soil particles
Root hairs
also help
Which critters at which trophic
levels affect your forest
management goals?
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Ecosystem resilience &
sustainability
Our Pacific
Northwest forest
ecosystems are
adapted to
various types of
natural
disturbances.
Photo: Washington DNR
Understanding Resiliency:
disturbance does not exceed system
ability to recover :self healing
• redundancy
• genetic diversity within & between
species
• refugia
Sustainability
• Sustainability is meeting present
needs without compromising the
future.
• Not pushing an ecosystem beyond
its ability to recover
Practices that drastically alter the operational
environment, such as terracing for site preparation, can
be successful, though not politically acceptable
Legacies
(the local spare parts bin)
As long as
enough
undisturbed
ecosystem
pieces
remain, the
system will
recover
Photo: Oregon State University College of Forestry
Sustainability is like good equipment
operation & maintenance…. Even better, with
good harvesting practices, forest ecosystems can quickly
repair themselves.
The right machinery and a
knowledgeable operator are
very important…
…as is leaving enough
of the right pieces intact.
Trees and forests are a renewable and
sustainable resource
These logs are the first commercial thinning of a stand
planted by the logger when he was in high school on a
brushfield cleared by his father.
Within stands or across landscapes,
sustainability takes human ingenuity
working with Mother Nature