Deforestation lecture

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					Deforestation lecture

1) to preserve, manage and restore forests
2) The transformation of forested lands by human actions represents one of the great
   forces in global environmental change and one of the great drivers of biodiversity
   loss. The impact of people has been and continues to be profound. Forests are
   cleared, degraded and fragmented by timber harvest, conversion to agriculture, road-
   building, human-caused fire, and in myriad ways. The effort to use… times.
   Deforestation has important… planet.
3) Accelerating into the remaining areas of undisturbed forest, and the quality. Today
   we examine global patterns in deforestation, assess the human and ecological costs of
   forest loss, and discuss some of the steps that can help to rectify this alarming
4) The USA has already experienced its wave of deforestation, with the exception of
   small areas in the west and Alaska. Our old growth forests were mostly harvested by
   1920, particularly in the East (Fig #). Pacific Northwest forests and UP Michigan
   forests were heavily cut after 1920 until quite recently, and harvest of old growth
   continues today in Southeast Alaska. Interestingly, deforestation rates at their peak in
   the Midwest were ~2% annually, about the rates now seen in Amazonia. At that rate,
   how much of existing forest will remain in 70 years? Just one-fourth. However,
   much forest re-growth has occurred in the eastern USA during the 20th Century,
   although these second-growth forests differ in structure and composition from their
   predecessors. Use slide 6 and its caption as Figure #

5) Some Definitions

    Deforestation: The conversion of forest to another land use or the long-term
     reduction of the tree canopy cover below a 10 percent threshold. Deforestation
     implies the long-term or permanent loss of forest cover and its transformation into
     another land use.
    Primary forest: is a forest that has never been logged and has developed following
     natural disturbances and under natural processes, regardless of its age.
    Secondary forests: are forests regenerating largely through natural processes after
     significant human or natural disturbance, and which differ from primary forests in
     forest composition and/or canopy structure.
    Disturbed forests: Any forest type that has in its interior significant areas of
     disturbance by people, including clearing, felling for wood extraction,
     anthropogenic fires, road construction, etc.
    Frontier forests: large, ecologically intact, and relatively undisturbed forests that
     support the natural range of species and forest functions (WRI definition).
    Forest plantation is one established by planting or/and seeding in the process of
     afforestation or reforestation. It consists of introduced species or, in some cases,
     indigenous species.
5) Forests provide important products for human use and consumption, and they provide
   valuable ecosystem services. Let's look at each in turn.

Forest Products

   Forests provide fuel. Some 83% of all wood use is for fuelwood (wow, check this).
    In poor areas where wood is scarce, people, usually women, walk long distances to
    gather wood for cooking.
   Forests provide useful wood products. Roundwood (whole logs) can be processed
    into building materials, or made into plywood products. Pulp is used not only for
    paper, but for a wide variety of products (including the “sponge” you used to wash
    your dishes).
   Forests are the source of numerous non-wood products, including bark, dyes, fibers,
    gums… waxes. Fruits, nuts and berries are harvested as food.

Ecosystem Services

   Forests influence climate. The within-year fluctuations in atmospheric CO2 in the
    temperate zone (link to mauna loa graph) include a spring-through-autumn decline
    due to plant photosynthesis during the growing season, and an autumn-through-spring
    rise in CO2 as respiration and decomposition exceed photosynthetic uptake. At a
    more regional scale, forests influence local climate and weather. Rain forests
    transport great quantities of water to the atmosphere via plant transpiration. (Water is
    taken up by plant roots, bringing dissolved minerals into plant tissues. Plants
    exchange gases with the atmosphere through openings in their leaves, and lose water
    in the same way. That water loss provides the plant with a means to transport
    materials upwards, and so is beneficial, so long as water loss is not excessive). Much
    of that transpired water replenishes the clouds and rain that maintain the rain forest.
    If the forest is cut, much more of that rain will become river water, flow to distant
    seas, and the region will become permanently drier. No rain forest can regenerate if
    this occurs. Forests maintain local climate and influence global fluxes of oxygen and
    carbon dioxide.
   Forests protect the top soil and husband important nutrients. A famous study of
    Hubbard Brook, New Hampshire (link) found that, after forest harvest, summer
    streamflows greatly increased (because the forest was no longer transpiring water)
    and nutrient outflow also increased greatly. The annual flood crest of the Amazon
    River at Manaus has increased over recent years without any concomitant increase in
    rainfall, presumably due to deforestation. Damaging floods are one frequent
    consequence of deforestation.
   Forests harbor tremendous biological diversity. They provide us with new crop
    varieties, medicines… nuts. A good example… recognized.

Carbon Sequestration
Tropical deforestation… burning. Deforestation thus is an important potential source of
carbon. But what if we allow forests to regenerate? As they grow, forests will store or
sequester carbon, and so carbon sequestration has become part of the global warming
debate. What is the current balance sheet – are the world’s forests a source or a sink for
atmospheric CO2? This is uncertain for three main reasons. We are not sure how much
forest is being burnt, vs the amount of regrowth. We don’t know enough about the fate
of deforested land, ie, how much is reverting to secondary forest. We don’t know how
forest disturbance is affecting soil and forest floor carbon stores. Lauira can we link to
gc1 or mac lecture?

The world’s tropical forests are disappearing at an alarming rate: about 100,000 km2 are
deforested each year, and another 100,000 km2 are degraded. Estimates are constantly
improving, based on satellite imagery, and deforestation rates change in response to
social and economic conditions, as well as quality and accessibility of remaining forest.
Landsat cannot see below the forest canopy, and so cannot detect below-canopy clearing,
whereas radar remote sensing can detect, eg, a coffee plantation beneath overstory trees.

   Tropical forests once occupied 16 million km2, today about 8-9 million km2 remain
   It is estimated that Latin America…
   In many countries the rate … is accelerating. For example… rain forest are
    disappearing rapidly.
   Only… intact

Move 7. Brazil to here

Add the following para and use slide 26

Roads usually accompany timber harvest, in order to move logs to sawmills and markets.
Even when tree harvest is highly selective, and much of the forest remains, it has been
found that the roads themselves have numerous adverse side-effects. As forests become
more open through thinning, they become drier, and more susceptible to fire. In wet
areas roads become pathways for surface runoff, and carry sediments into streams,
destroying aquatic life. Culverts installed where roads cross rivers often block fish
passage, and have devastated salmon populations in the western USA. In tropical forests,
roads allow hunters and poachers much greater access, resulting in the large and very
serious bushmeat trade that is emptying tropical forests of their wildlife.

Causes of Deforestation

Deforestation has many causes. Population pressures, profits, and internal social and
political forces can all push up the rate of forest loss. Access to markets, requiring roads
and capital, is an additional powerful force, recently expanded due to the suite of changes
referred to as globalization. Poor countries with expanding populations, inequitable
distribution of wealth and power, and possibly corrupt governments are especially
 In Indonesia, powerful families allied with government rulers control large and highly
    valuable timber concessions. These forests are being rapidly liquidated, at enormous
 In Brazil, many of the rural poor are moving to cities for work, and not finding it.
    Productive farmland is controlled by a wealthy elite with a long history of land
    ownership, and so many of the rural poor are landless. By opening its frontier – the
    Amazon forest - to its landless poor, Brazil seeks to provide a safety valve for what
    otherwise might be an explosive political situation.
 In many areas, poor people have few options to make income, and forests have few
    protectors, and so land is cleared for agriculture and valuable timber is sold for profit.

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Forest Management and Recovery

Forest management may have many goals. Under rotation harvest, the goal typically is
to maximize annual harvest while ensuring that the area harvested is consistent with
forest regrowth rates and total area under management. This might result in a second
harvest of the same forest plot after some 60-100 years. Forests on federal and state
lands are usually managed according to multiple use doctrine. This means that in
addition to forest harvest, the land is available for recreation and maintains a healthy
forest ecosystem. Managing to protect biodiversity and to restore pre-settlement
conditions are relatively recent goals. In many parts of the world forests may be used by
indigenous people for subsistence hunting, forest harvest, and as a place to live. This
adds yet more considerations, and more stakeholders, to the challenge of forest

Forest restoration may seek to restore the system to a near-natural or completely natural
state, or to restore many aspects of the structure and function of an undisturbed forest.
The latter is usually referred to as rehabilitation, to emphasize that the desired endpoint is
not necessarily that of pre-settlement conditions.

Forest management in the USA often involves the controversial role of fire, and whether
to attempt to direct the course of forest succession. Most forests in the lower 48 states are
relatively young second-growth, and may have developed under an unnatural degree of
fire suppression. In the upper Midwest, for example, aspen covers much of what was
once white pine. Roughly 80 years old, these aspen forests are at the age when they are
likely to die. It is uncertain what type of forest will replace them. Within oak-maple
hardwood forests, the overstory is dominated by oaks, whereas the seedlings are
dominated by maple. To maintain oak forests, some combination of fire and thinning is
needed to favor recruitment by oaks.
Fire plays a major role in many forest types, including some that are highly fire adapted.
The jackpine of Michigan, for example, releases its seeds only after fire heats its cones.
Fire suppression has been US Forest Service policy since some devastating fires of the
1950s brought calls for fire management. Since then, fuelwood on the forest floor has
accumulated and people attracted by scenic settings have increasingly built houses in
wooded areas. As a consequence, calls for fire suppression are even stronger, and the
human costs of fire are even greater than before.
Use slide 28 and caption here

Forests often will recover on their own, but perhaps not in the direction or as quickly as
we might prefer. The old growth spruce-hemlock forests of Southeast Alaska appear to
recover toward their original state, but it is hard to say how long this will take. After all,
extensive clear-cuts first took place only some 50 years ago, so there are no forests that
have fully recovered. Best estimates from comparisons of plots of different ages, some
caused by long-ago natural disturbances, suggests 200-400 years. It often is said that
tropical forests will never recover from deforestation, especially if the land is burned and
the top soil is disturbed. This may be true in some instances, but examination of lands
abandoned 50, 100, or more years ago suggests that we should be more optimistic. An
ambitious plan to restore a dry forest (one that sheds its leaves in the dry season) in
Guanacaste, Costa Rica, serves as a good example. Using fire and grazing to control
invasive plants, and working with a detailed knowledge of forest ecology, workers there
hope to return this area to its original forested state. In other regions of the tropics, native
seedlings are grown in nurseries and planted in forest openings to help speed recovery.

Insert slide 32 here

Insert these links

Extent of tropical deforestation website

GC1 lecture on tropical forests

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