When you picture a forest
in your mind, what does it look like? Your answer might depend on
the biome you live in. There are many biomes, or living communities
on the earth's surface such as rain forests, grasslands, deserts,
woodlands, savanna or temperate deciduous forests.
Trees grow all over the
world. They must adapt to different types of conditions from the icy
cold to the desert dryness. For example, mangrove
trees grow in tropical regions along the sea. In fact, they are
sometimes called the forests of the sea. The roots of the mangrove
tree are adapted to cope with the soft mud underwater by growing
downwards like stilts to anchor it in place. Some roots grow upwards
until they are sticking out of the water in order to reach oxygen.
The roots also have a special filtering system to remove the salt
from the seawater they take in. How are the trees adapted to the
environment where you live?
Many people in the northern or
mountainous regions of the United States might picture coniferous
or boreal forest (RED)in their minds. Other people, from the
eastern United States may envision deciduous
forests (PINK), found within the United States' temperate zone,
recognizable by their broad leaves which change color and fall off
when the days get shorter and the weather turns colder in the fall.
You most likely have heard about tropical rain forests. Did you know
that there are rain forests in Oregon and Washington? These forests
receive as much rain as tropical wet forests (GREEN) but they are
located in northern laditudes and are called temperate rain
But in the countries to the south of the
United States, other kinds of forested areas exist which you may
have heard a great deal about, but have never seen.
You have probably heard and read a lot
about tropical rainforests, but did you know that there are
many different kinds of tropical forests? When we use the term
"tropical" we refer to the area between the Tropics of Cancer and
Capricorn. Because this region of the earth receives the most "direct"
rays of the sun throughout the year, the temperatures usually
stay fairly warm.
Between the Tropics of Capricorn and
Cancer, there are many types of forests such as: Moist Tropical
Forests, Dry Tropical Forests, Riverine Forests, Mangrove
Forests, and Cloud Forests.
There are many factors which influence
the forest type. This is true even with a specific forest biome
(rainforest, coniferous, etc.) Forest type vary by rainfall,
temperature, type of soil, animal life, the number of dry months,
altitude, and slope. For example, short scrub forests grow in
tropical regions with little rainfall. Mangroves grow along
shorelines where fresh river water and sea water mix together. In
high-altitude mountainous areas, coniferous forests and cloud
forests ( in the tropics) can thrive.
The map below shows how forests
ecosystems change as Latidude and Altitute
Defining the boundaries between types of
tropical forests can be difficult. For example, with an increase in
altitude, a tropical rainforest may gradually blend with cloud
forest. As a forest nears the shore, it may slowly become dominated
by mangrove forest. Therefore, the term "tropical rainforest" is
sometimes just an easy way to refer to a variety of different
habitats that exist between the tropics of Cancer and Capricorn.
Overall, tropical forests cover about 1,700 million hectares, an
area about the size of South America.
All of the forests mentioned are
threatened by logging, intensive resource use, and urban
development. From the coniferous forests of the Himalayas to the
Guatemalan mangroves, forests are in retreat. The New Forests
Project works in many capacities to reduce deforestation in tropical
regions. Because many local farmers and communities need forest
products such as lumber, food, and fodder to survive, it is not as
simple as restricting resource use. The New Forests Project has
found that it is necessary to provide the local populations with
alternative sources of tree products so farmers have the opportunity
to let degraded areas regenerate.
Trees and soil
Trees are essential to the maintenance of
healthy soil. Tree roots dig deep into the ground, which helps to
aerate, or provide oxygen to the soil. The roots can loosen hard mud
or rocks under the topsoil, which makes it easier for burrowing
animals, worms and microorganisms to tunnel and aerate the soil as
well (When animals, plants and microorganisms aerate soil
they create tiny air pockets that can be filled by roots or water.
Healthy soil is well aerated!). Water that penetrates the topsoil
can then drain deeper into the ground. This increases the rate at
which rainwater infiltrates and recharges the groundwater,
an underground reserve of water.
When trees lose their nuts, fruits, or
leaves, these materials drop to the forest floor. If not eaten, they
decompose and the organic matter is returned to the soil, which is
vital in terms of keeping the soil nutrient-rich. Dead trees also
decompose over time, and return their nutrients to the soil.
The shade keeps the harsh sunlight from
penetrating the ground, allowing it to maintain an appropriate
moisture level. The tree trunk and canopy also protect the soil from
harsh winds. Trees maintain soil fertility when nutrients drawn up
by their roots are recycled into the top layers of the soil by leaf
Trees also help keep the soil in place by
means of their strong root systems. This, as well as a tree's
protective canopy, prevent soil erosion, which can have some very
serious consequences. A half-hour thunderstorm in tropical forests
can produce forty times more rain than the average northeastern U.S.
thunderstorm. Therefore, these heavy downpours wash away more soil
than anywhere else in the world. When it rains on slopes, hills or
mountains that have been deforested, the rainwater will run off,
carrying with it much of the topsoil from the hills. This will
happen if you remove any type of forest (tropical, coniferous,
deciduous). You may be thinking "Isn't all dirt the same?" But it
takes one hundred years for nature to produce just one inch of
topsoil, which holds the nutrients needed for plant regeneration.
Soil erosion has impoverished more than
one-half of all agricultural land, causing farm productivity to
decline sharply. When the topsoil is washed away, so too are its
nutrients and its ability to sustain crops.
Where does this topsoil end up?
Downstream is the easy answer. The soil continues to wash away until
in ends up clogging rivers and waterways. The buildup of soil in
rivers becomes so great, many dry up, and the local people and
animals are deprived of a life giving resource. The riverbeds can
also expand to a level where flooding occurs during heavy rains.
Water reservoirs become filled with silt- the fine soil carried down
the river or stream - and they are unable to store the amount of
water they were designed to hold. Siltation and filling reduces
their usefulness for flood protection, power generation, it also
decreases fish populations and alters river flows.
Trees and the Hydrological Cycle -- or
Have you ever been walking on a hot day
in a field or village then entered a forest or heavily shaded area?
It feels much cooler and even damp!! Why do you think this is
Trees are often considered natural
sponges which regulate the earth's water supply by holding water.
Forest waste matter, such as decomposing leaves or humus, slows down
surface evaporation from the soil. Rain first falls on leaves and
plants rather than directly hitting the soil, decreasing the rate of
water and soil erosion.
Deforestation leads to a decrease in the
amount of water absorbed by the soil. Less water seeps down into the
soil to recharge the groundwater. This leads to an absence of water
available during the dry season and freshwater springs can dry up.
Trees also hold water with their vast root systems, by creating air
pockets deep in the soil. These pockets hold water during heavy
Forests help regulate the water in the
air through a process called transpiration.
They absorb thousands of gallons of water into their roots. The
water is carried up through the trunk and into the branches and
leaves for food. Excess water and nutrients are then released
through the leaves back into the air.
When the air becomes saturated with
enough moisture, clouds form and if enough moisture is
transpired into the air, rain will fall. This begins the water
cycle all over again. When a forest is destroyed, this release
of moisture back into the air is lost, which results in less
rainfall for that area in the future.
To see the tiny holes, or stomata,
in the leaves through which leaves transpire water, you must look
under a microscope. However, if you wrap a broad-leaf plant in clear
plastic, and place it in the sunlight, in a few hours, you will see
moisture or condensation clinging to the inside of the bag. This
moisture was given off by the leaves much like the moisture excreted
from your skin when you perspire.
Trees and Climate
Many human activities, such as modern
farming, the burning of fossil fuels or cutting down and burning
forests, release large amounts of gas into the atmosphere. These
gases are referred to as greenhouse gases because they act like the
glass covering of a greenhouse, absorbing solar radiation and
trapping it inside. Greenhouse gases, such as Carbon dioxide (CO2),
absorb some of the sun's energy which would otherwise be released
back into space.
The Greenhouse Effect
Sunlight pentrates the atmosphere and
warms the Earth's surface. The Earth then radiates some of this heat
back into the atmosphere. Some of this heat escapes into space and
some is reflected back to earth as watervapor and greenhouse gases
absorb it. As greenhouse gases increase more heat can be trapped
near the Earth's surface
This build-up of carbon dioxide could
cause the planet to heat up. It is estimated that clearing and
burning tropical forests accounts for about 20% of the increase in
carbon dioxide levels in the atmosphere.
Trees absorb carbon dioxide to make food
during the process of photosynthesis. Using energy from the sun,
green plants break apart carbon dioxide and water molecules and
rearrange the loose atoms to form sugar. Trees use sugar as food for
growth and energy. Oxygen, which is what humans must inhale to
survive, is left over from this process and released into the
atmosphere. During the nighttime, this process is reversed. Trees
absorb oxygen and emit carbon dioxide. By planting trees we can
reduce the amount of CO2 in the atmosphere and possibly prevent
global warming from happening.
Scientists disagree on how much these
greenhouse gases will affect the global temperature. Some scientists
predict that the average global temperature could increase 3.6
degrees Fahrenheit in the next seventy years due to global warming.
This may not seem like a very drastic change, but some scientists
believe it is a big enough change to melt the earth's polar ice
caps, leading to a rise in sea levels which could flood coastal
cities around the world. A rise in temperature could be enough to
endanger the crops we rely on for food. It could dry up the lakes
and rivers in some areas which provide water to crops, towns and
Agro forestry is a type of farming. It is
a type of farming in which crops, like corn, beans and vegetables
are planted alongside trees. There are a number of reasons why this
is done in addition to a number of different ways it can be
accomplished. It can be used on small farms or large
Some farmers use a method is called live
or vegetative barriers on hillsides to prevent soil
erosion while they are growing their crops. The trees, mostly
their trunks and roots systems, form a "barrier" which stops the
soil from moving downslope. As the trees become established, a flat
area of high quality top soil forms behind them. Live barrier
farming systems require a great deal of maintenance, but can be
highly effective for growing the crops necessary for the farmers to
survive. This type of farming is also called contour
farming, because farmers plant trees or vegetation along the
contour lines of a hillside.
Sometimes farmers grow trees with crops
for protection from the strong winds. Strong winds can carry
nutrient rich topsoil away from farmers' fields and deposit it
hundreds of miles away. Trees planted in shelter-belts, which shield
the farmers fields, offer effective protection from the problems of
trees such as, palm or leucaena trees can also be grown
with crops that will not grow well in direct sunlight. Cocoa,
coffee, pepper plants all need shade to be productive.
Other farmers grow trees with crops to
provide green manure -- regular manure is usually made from
horse, cow, chicken or goat dung, green
manure is made of the leaves of certain kinds of tree or plant
species to fertilize the soil where crops are planted. The leaves of
some agroforestry tree species can also be used as feed for cattle
or other livestock. When leaves are used for animal feed it is
called fodder. The agroforestry tree
species used by the New Forests Project are fast-growing,
tree species. Fast growth makes them an excellent choice to use in
agroforestry systems because they provide farmers with large
quantities of lumber, green manure and fodder in a very short time
-- a year or two in most tropical areas.
Nitrogen is the most abundant element in
our atmosphere, but why is it important? Nitrogen is a vital
component in the production of protein. Protein is one of the
nutrients that plants and animals need to grow, survive and
Although there is a large amount of
nitrogen in the air, approximately 69,000 metric tons of
nitrogen per hectare in the atmosphere, plants are unable to use it
because it is chemically inert (bound to other molecules, such as
oxygen). In fact in the United States and other countries, many
farmers add nitrogen in the form of fertilizer to help plants grow
faster and stronger. In areas that have been degraded or that lack
sufficient chemical or natural fertilizer, there may be very little
nitrogen in the soil for the plants to use for the production of
protein. In these cases many trees have a very hard time
establishing themselves and developing successfully.
The New Forests Project utilizes
and distributes trees that can fix nitrogen from the air that is
present in the soil surrounding their roots. But the trees cannot
fix nitrogen alone they need the help of bacteria called
Rhizobia to secure the nitrogen for them.
what Rhizobia working with tree roots looks like!
These bacteria "infect" the young root
cells of the trees and through a symbiotic relationship they form
root nodules -- a nodule is a similar to a small compartment or pod.
The bacteria live in the root nodules and produce nitrogen for the
tree through nitrogen fixation. The trees supply the bacteria with
nutrients and other compounds necessary for their survival. This is
called a symbiotic relationship because both the tree and the
Rhizobia help each other. Can you think of any other symbiotic
relationships? Peas, beans, and clover are other plants called
legumes which have the ability to fix nitrogen.
Only certain tress have the ability to
fix nitrogen. In the United States Robinia psuedoacacia
(black locust), Gleditsia triacanthos (honey locust) and
Alnus species (Alder) are trees that can fix nitrogen. In the
tropics Acacia, Leucaena and Prosopis species
are examples of nitrogen fixing trees (there are many more than this
When grown properly these species can;
thrive on and regenerate degraded soils where other species may
not survive, allow farmers to save money by reducing the need to
purchase man-made fertilizer, stabilize soils, and provide fodder
The New Forests Project
distributes and utilizes a number of leguminous trees species in our
projects to help farmers regenerate and replenish depleted soils.