Contents: Major forest types Coniferous forest Temperate broadleaf forest Tropical forest Forest structure Coniferous forest structure Deciduous forest structure Tropical forest structure Forest stratification and animal life Function

5. FORESTS
• Major forest types
– Coniferous forest
– Temperate broadleaf forest
– Tropical forest
• Forest structure
– Coniferous forest structure
– Deciduous forest structure
– Tropical forest structure
• Forest stratification and
animal life
• Function

6. FORESTS
Major forest types
There are three general, but highly diverse
major forest types worldwide:
• coniferous forests,
• temperate broadleaf forests, and
• tropical forests.

7. Coniferous forests
Conifers are cone-bearing gymnosperms—resinous trees with
dark green, needle /scale-like leaves.
Most conifers are evergreen i.e. year-round foliage. They
photosynthesize year-round; whenever conditions are favorable

8. The coniferous forest type has five distinct
ecosystems(as described here for North America):
1. The taiga and boreal forest - the largest and most
expansive coniferous forest which is generally
limited by the summer and winter positions of the
Arctic front.
The taiga can be further subdivided into four habitat
types: two of which are ecotonal regions of boreal
forest-tundra habitat & mixed hardwood-conifer
forest along the northerly and southerly limits,
respectively.
The remaining two habitats are open boreal
woodland (black spruce in damp areas) and the main boreal
forest (continuous stands of white spruce and balsam fir)

9. 2. Temperate needleleaf rain forest - the most luxuriant
of the coniferous forests, features trees of
unparalleled size and longevity.
Overstory trees can be more than 50 meter tall and
have diameters greater than two meters.
Longevity is generally greater than 500 years.
These characteristics are related to the excessive
moisture regimes (more than 600 cm annually with
about a third of this occurring as fog drip) and mild
temperatures.

10. 3. Woodlands - characterized by the presence of pinyon
pine and juniper and a well-developed understory.
This type has been subjected to much human
disturbance.
4. Southern pine forests– found in the southeastern
United States and are not representative of climax
vegetation.
They occur on sandy soils and are maintained by
frequent fires.

11. 5. Montane coniferous forests-these forests are
associated with mountainous regions.
The subalpine forest is found at the higher elevations
and is dominated by spruce and fir species.
The montane forest is found at lower elevations and is
dominated by pines and some spruces.
Montane forests are relatively warmer, wetter, more
species-rich, and more productive than subalpine
forests.
The existence of coniferous ecosystems is typically
related to regions of modest environmental rigor,
which have cool temperatures, low rainfall, soils of
poor quality, and/or fire frequency.

12.  These generalizations must be taken with some
caution.
High rainfall and mild temperature regimes
characterize the temperate rain forest, yet the soils
are thin and poor in nutrients.
 The southern pine forests occur in regions of
ample moisture and warm temperatures, yet owe
their existence to nutrient-poor, sandy soils and
the prevalence of fire.

13. • The air masses that drop their moisture on the western
slopes of the Coastal Range then descend the eastern
slopes, gain heat, and absorb moisture, creating
conditions that produce the Great Basin Desert.
• The same air rises up the western slopes of the Rocky
Mountains, cools, and drops moisture again, although
far less than on the Coast Range.
• Here, in the Cascade, Wasatch, Rocky, and Sierra
Nevada mountains, several coniferous forest
associations develop.
• In the southwestern United States these coniferous
forest occur between 2500 and 4200 m elevation.
• Rocky Mountains (winters are long and snowfall is
heavy) = subalpine forest

14. Temperate broadleaf forest

15. o The temperate broadleaf forests have been used
extensively by mankind for centuries; most of what
exists today is second- and third-growth forest.
o In light of the daily, and winter and summer climatic
extremes that must be endured by species in these
forests, the use of the term “temperate” is somewhat
misleading.
o They are exposed to droughts and, in places,
flooding.
o In spite of their intemperate “temperate” environment,
temperate forest ecosystems are able to maintain high
productivity.

16. The temperate broadleaf forests occur in three
general forms:
1. Temperate deciduous forests – Temperate deciduous
forests once covered large areas of Europe, China,
parts of South America, the Middle American
highlands, and eastern North America.
The deciduous forest of Europe and Asia have largely
disappeared, cleared for agriculture and settlement.
The dominant trees include European beech, oak,
ashes, birches, and elms.
Because of glacial coverage during the ice ages, the
diversity of tree species in European deciduous
forests is lower than that of North America and

17. 3. Temperate broadleaf evergreen rain forests - these
forests occur in subtropical areas, such as the Florida
Keys, Australia, South America, etc.
Species include as magnolias, palms, eucalyptus, and
live oaks.
The oaks and other trees support an abundance of
epiphytes and the lichen, Spanish moss.
o The temperate broadleaf forests have been used
extensively by mankind for centuries; most of what
exists today is second- and third-growth forest.
o In light of the winter and summer climatic extremes
that must be endured by species in these forests, the
use of the term “temperate” is somewhat misleading.

18. Tropical forests experience a steady year-round temperature of about
23o
C and a wide variation in rainfall, climatic conditions that are reflected
in a diversity of vegetation patterns.
The tropical region contains twice as many Holdridge life zones as the
temperate zone and seven times the number of the boreal zone.

19. The tropical forests occur in four forms:
1. Tropical rain forest - the tropical rain forest is found in
at least 30 to 40 types including the monsoon forest,
the evergreen savanna forest, the evergreen mountain
forest, the tropical evergreen alluvial forest, and the
lowland tropical rain forest.
They once formed a worldwide belt around the
equator.
Today, the largest continuous rain forest is found in
the Amazon basin; other major areas are in west and
central Africa and the Indo-Malaysian regions.
These forests are found where temperatures are
constantly high and every month is wet.
They support nearly half of all known plant and animal
species.

20. 2. Tropical montane rain forest - found in mountainous
regions above the lowland tropical rain forest.
The lower montane forest is found on the highest
mountains and is an ecotone between the broad
leafed-dominated lowland forest (with an uneven
billowing canopy) and the small leafed-dominated
upper montane forest.
The montane forest has a lower, more even canopy,
a dense lower canopy, and smaller trees with
gnarled limbs heavily covered in bryophytes and
ferns.

21. 3. Tropical seasonal forest - these forest grade into
semi-evergreen and semideciduous seasonal
forests.
They are characterized by less rainfall, more
variable temperatures, and
a dry season during which about 30% of the upper
canopy species lose their leaves.

22. 4. Tropical dry forest - these forests make up about 42% of
all tropical forests, with the most found in Africa and on
tropical islands.
Most of the original forests have been converted to
agriculture and grazing lands or have regressed through
disturbance to thorn woodland, savanna, and grassland.
These forests experience a dry period, with the length
depending on latitude.
The greater the distance from the equator, the longer is
the dry season.
During the dry period, trees and shrubs drop their
leaves. Before the start of the rainy season, which may
be wetter than the wettest time in the rain forest, the
trees begin to leaf out.

23. Forest structure
The structural features of a forest are built upon the
vertical stratification created by the amount of space
occupied by trunks, branches, twigs, and leaves at
different levels or heights above ground. There are
four general strata:
1. Canopy - intercepts the bulk of solar radiation.
2. Lower or understory tree canopy.
3. Understory shrub layer.
4. Herbaceous or forest floor layer.

24. o Tropical forests may also have an emergent layer.
o All strata are not necessarily found in all forests.
The highest temperatures and most light are found in the
upper canopy. Temperatures tend to decrease through
the lower strata and change through the 24-hour period.
Light intensity is attenuated through the forest canopy to
only a fraction of full sunlight at the forest floor.
The lowest humidity in the forest is a few feet above the
canopy, where air circulation is best and the highest is
near the forest floor.
Humidity in the temperate deciduous forest interior is
highest in summer because of plant transpiration and
poor air circulation.

25. The amount of dead wood changes with tree mortality
and disturbances and never achieves an equilibrium.
Woody litterfall usually increases over time and
becomes most prominent in old deciduous and
coniferous temperate forests.
However, temperate broadleaf deciduous forests have a
lower input, a faster decay rate, and thus a lower
accumulation of dead wood and nutrients on the forest
floor.
Standing dead trees provide essential nesting and den
habitat for cavity-nesting birds and mammals.
Decaying logs are an important rooting medium for tree
seedlings, especially conifers.

26. Coniferous forest structure
Coniferous forests fall into three broad classes
according to growth form that influences their
structure:
1. Pines with straight, cylindrical trunks, whorled
spreading branches, and a crown density that varies
from the dense crowns of red and white pine to the
open thin crowns of Virginia, jack, Scots, and
lodgepole pine.
2. Spire-shaped evergreens, including spruce, fir,
Douglas-fir, and (with some exceptions) the cedars,
with more or less tall pyramidal open crowns,
gradually tapering trunks, and whorled, horizontal
branches.
3. Deciduous conifers, such as larch and bald cypress,
that have pyramidal, open crowns and shed their
needles annually.

27. • Coniferous forests
Vertical structure and stratification in coniferous forests

28. Vertical structure is not well developed in many
coniferous forests-
Because of high crown density and deep shade, the lower
strata are often poorly developed in spruce and fir
forests.
Pine forests with a well-developed high canopy may lack
lower strata.
However, older stands and forests of open-crowned pines
many have three strata: an upper canopy, a shrub layer,
and a thin herbaceous layer.
The litter layer in coniferous forests is usually deep,
poorly decomposed, and lies on top of instead of being
mixed with the mineral soil.
It can inhibit the germination and development of woody
understory and herbaceous plants.

30. Temperate deciduous forest structure
Highly developed, uneven-aged and older even-aged
deciduous forests usually consist of four strata:
1. The upper canopy of dominant tree species.
2. Below the upper canopy is the lower tree canopy of
saplings and understory trees.
3. The shrub layer.
4. The ground layer consisting of herbs, ferns, and
mosses.
The litter layer is variable, depending on the lignin-to-
nitrogen ratio. It ranges from a thin, rapidly
decomposing layer in sugar maple and yellow-poplar
forests to more slowly decomposing oak leaves.

31. • Temperate deciduous forests
Vertical structure and stratification in eastern deciduous forest

32. Even-aged stands (trees all of similar age) of trees are
typically the results of fire, clear-cut logging, and other
large-scale disturbances.
These often have poorly developed strata early in their
development because of dense shade.
The low tree and shrub strata are thin,
and the ground layer may be poorly developed, except in
gaps, until the stand approaches maturity.

33. Old-growth coniferous and deciduous forest structure
Old-growth forests are often, compositionally and always
structurally, different from earlier successional stages.
o Old-growth consists of a wide range of tree sizes and
spacing that results in a high degree of patchiness and
heterogeneity.
This patchiness results from some degree of disturbance
over time within the stand.
Old-growth stands are dominated by long-lived individuals
and contain significant amounts of woody debris and
downed logs.
Old-growth stands possess more diversity in structure
and function than secondary forests, and are
characterized by highly evolved complex relationships
between animals and plants.

34. Some forests (particularly eastern deciduous forest) may achieve old-growth
stage at 150- to 200-years.
Other species and stands may not arrive at old-growth stage until
much later.

35. • Old-growth coniferous forests, especially boreal and
western coniferous forests, support
microcommunities of algae and lichens in the canopy.
• These rather complex microcommunities include
primary producers, consumers, and decomposers.
• Cyanophycophyllous lichens fix atmospheric
nitrogen.
• Organic nitrogen lost through leaching from lichens
combines with canopy moisture to form a dilute
organic solution that in turn is taken up by
microorganisms and other canopy epiphytes.
• Part of this microbial production is consumed by
canopy arthropods.

37. Tropical rain forest structure
The tropical rain forest has been divided into five
general layers:
1. Emergent canopy - Uppermost or emergent layer that
consists of trees 50 to 60 m or more high. Their
crowns rise above the rest of the forest to form a
discontinuous canopy.
2. Canopy - Main canopy that consists of a more or less
continuous layer of trees 24 to 36 m high.
3. Lower canopy - Lower tree stratum that consists of a
more or less continuous layer of trees 15 to 24 m high.
4. Shrub and young tree layer - A generally poorly
developed layer of shrubs and young trees that can
exist in the deep shade of the understory.
5. Ground layer - A layer composed of tall herbs and
ferns.

38. Stratification of tropical rain forests in often poorly
defined with no clear demarcation between layers,
except for the emergent canopy layer.
This results from a combination of tree species that
have the same growth plan but different sizes, or
species that mature at different heights. Other
individuals become dwarfed because of unfavorable
growing conditions.
A conspicuous part of the rain forest is plant life
dependent upon trees for support, including epiphytes,
climbers, and stranglers.

39. Epiphytes attach themselves to a host tree and obtain
their nutrients from air, rainwater, and organic debris
trapped by their aerial roots or leafless bases.
Some epiphytes are important in recycling minerals
leached from the canopy.
Climbers are vinelike plants that reach the tops of
trees and expand into the form and size of the tree
crown.
Climbers grow prolifically in openings, giving rise to
the image of the impenetrable jungle.
Stranglers start life as epiphytes.
They send their roots to the ground and increase their
stems in number and girth until stranglers encompass
the host tree and claim the crown limbs as support for
their own leafy growth.

41. Forest stratification and animal life
The distribution of animal life in the forest is strongly
influenced by forest stratification and microclimate.
Coniferous forests
In the coniferous forest animal life varies widely
depending on the nature of the tree stand.
o Mites dominate the soil invertebrate litter fauna.
Earthworm species are few and their numbers low.
o Insect populations, although not diverse, are high in
numbers and, encouraged by the homogeneity of the
stands, are often destructive.

42. o A number of bird species are closely associated with
coniferous forests.
o In general, the coniferous forests of northeastern and
southeastern North America and the Sierra Nevada
Mountains support the richest avifaunas.
oBird densities are highest in the Pacific Northwest and
lowest in immature northeastern coniferous forests.
o Except for strictly boreal species, such as the pine
marten and lynx,
mammals have much less affinity for coniferous forests.

44. Deciduous forests
The greatest concentration and diversity of life in the
forest occurs on and just below the ground layer.
o Soil and litter invertebrates are found in the upper levels
of soil.
o Mice, shrews, ground squirrels, and forest salamanders,
burrow into the soil or litter for shelter and food.
o Larger mammals, such as deer, live on the ground layer
and feed on herbs, shrubs, and low trees.
Other species occupy the upper strata—shrub, low tree,
and canopy layers.
o Birds move freely among several strata, but they favor
one layer over another.
o Squirrels inhabit the canopy, and woodpeckers,
nuthatches - range up and down tree trunks in a space
bounded by shrubs below and the canopy above.

45. Tropical rain forests
Stratification of animal life in the tropical rain forest is
pronounced.
Harrison (1962) recognized six distinct feeding strata:
1. A group feeding above the canopy that consists
largely of insectivorous and some carnivorous birds
and bats.
2. A top of the canopy group including a large variety of
birds, fruit bats, and other species of mammals that
feed on leaves, fruit and nectar.

46. 3. Below the canopy in the zone of tree trunks that
includes birds and insectivorous bats.
4. Also in the middle canopy are found scansorial
mammals that range up and down on the trunks,
entering the canopy and the ground zone to feed on
the fruits of epiphytes, on insects, and on other
animals.

47. 5. Large ground dwelling animals that include large
mammals and a few birds, living on the ground and
lacking climbing ability, that can reach up into the
canopy or cover a large area of forest.
They include the large herbivores and their associated
carnivores.
6. The small ground and undergrowth animals, birds and
small mammals capable of some climbing, that search
the ground litter and lower parts of tree trunks for
food.
This stratum includes insectivorous, herbivorous,
carnivorous, and mixed feeders.

48. Function
The structure of a forest, built from the accumulation
of carbon (net primary production) at the various
levels, provides the framework for the functional
processes critical to net primary production—nutrient
cycling. The various processes include:
1. Atmospheric inputs of dust, precipitation, and
nitrogen fixation and outputs in drainage water;
2. Uptake of nutrients from the soil and return of
nutrients to the soil by plants through leaching,
litterfall, and death of individuals and decomposition;
and
3. Redistribution of nutrients within the plant, or internal
cycling. The uptake of nutrients includes those
nutrients returned to soil made available through
leaching and decomposition, and nutrients from soil

49.  FUNCTION
A schematic diagram of
nutrient cycling in a forest

50. Nutrient cycling varies through three general stages
of forest development.
1. The early stage involves the growth of biomass in
which most of net primary production goes into the
increase in photosynthetic tissues (leaves) and the
metabolic transport system (phloem and sapwood).
In this stage of growth, up to 20 years, uptake of
nutrients from soil is the greatest.
2. From this point, up to 50 or more years, depending on
the species, most of the net primary production goes
into the development of support tissue (the
heartwood) and large amounts of nutrients are
recycled through the tree, reducing dependence on
uptake from the soil.
As the tree matures, most of the net primary
production goes into maintenance and litterfall.

51. 3. Older forests accumulate more nutrients in biomass
than younger forests, and the rate of increase in
nutrient storage declines.
Return of nutrients from plant to soil is maximum.
• Nutrient cycling in the temperate deciduous forest
differs from that in coniferous forest because trees
annually return foliage as litter to the forest floor.
There is no accumulation of nutrients in foliage over
time.
• The efficiency of nutrient cycling is reflected in the
balance between inputs to the biological system and
outputs or losses from the system through
streamflow from the watershed.

52. Here is an example of
macronutrient
accumulation over time
in a loblolly pine stand.
At an early age loblolly
pine exhibits a rapid
accumulation of
nutrients.
From 20 to 40 years,
nutrient accumulation
slows as internal cycling
increases.
After 40 years,
accumulation of
nutrients declines as
tree growth slows,
becomes less dependent
on uptake, and returns a
greater portion to the
soil through litterfall.