Land and Food Resources I
Potential Test Questions
1. What five ecosystem services are provided by natural
areas. Discuss.
2. Discuss the ‘tragedy of the commons,’ the ways in
which we have ‘commons’ in the United States, and
solutions to the tragedy.
3. How can overgrazing affect desertification. (Make
sure to explain why grasslands can tolerate grazing,
how overgrazing effects grasslands, and what
desertification is).
Potential Test Questions
4. Discuss tropical deforestation and its causes. Explain
swidden agriculture in your discussion.
5. What are the BLM and USFS? What policies have
they had in place that are harmful to U.S. ecosystems.
Explain.
Ecosystem Services of Natural Areas:
1.
2.
3.
4.
5.
Wildlife habitat (protect species)
Flood and erosion control
Soil formation/maintenance
Groundwater recharge
Recycle wastes (nutrient cycles)
and break down pollutants
Pasture and Open Rangeland
Predominantly grasses
with a fibrous root
system. Rangelands
occupy about 26% of
the world’s land
surface.
Pasture and Open Rangeland
There is twice as much permanent grazing land as area
given to agricultural crops in the world. Much of the
western Great Plains and the Prairie provinces of
Canada fall in this category.
Pasture and Open Rangeland:
Carefully managed, grazing can be sustained in grasslands
(with the loss of a few grazing-intolerant plant species),
because most species are tolerant of being grazed.
For the U.S.,
rangeland/prairies have more
species of plants, and more
threatened species of plants,
than any other biome type.
Pasture and Open Rangeland:
Benefits of grazing include:
Hooves create seed-to-soil contact
Natural grazers break soil crusts that keep seeds from
growing
Grazers trample standing vegetation into mulch
Grazers act like living compost piles, turning vegetation
into high-quality fertilizer
By pruning stale growth, they keep forage plants at peak
production
Pasture and Open Rangeland:
Effects of overgrazing grazing
include:
Compacting soil thus
preventing seeds from
germinating and water from
seeping into soil.
Overfeeding on plants not
allowing them time to
recover and adequately root.
Overgrazing
Overgrazing is when plants are consumed such that the
plant community does not quickly recover.
1/3rd of the world’s
range is severely
degraded by
overgrazing, making it
the largest cause of soil
degradation.
Overgrazing
The first symptom of overgrazing is the loss of palatable
species of herbs and grasses. Continued overgrazing
compacts the soil, strips the ground bare, and leads to
erosion.
Desertification
Continued degradation leads to a fertile land becoming more
desert-like.
Without plants to
hold soil moisture,
surface runoff
increases, wells
dry, the
microclimate
becomes
inhospitable for
plants, and deserts
occur.
Desertification
In Africa, deserts have increased by 50 million hectares,
and humid or semiarid lands have decreased by that
amount. Is human activity responsible?
Remember the
Tragedy of the
Commons
Any commonly held
resource becomes degraded
or destroyed because the
narrow self-interests of
individuals tend to outweigh
the public interests.
U.S. Rangelands
Bureau of Land Management (BLM): 200 million acres
U.S. Forest Service (USFS): 50 million acres
60% of rangeland is privately owned.
55% of public rangelands are in poor condition (sage,
mesquite, cheatgrass, and cactus).
Grazing fees: grazing permits on BLM or USFS land was
$1.35 per animal. It costs them $3.21 per animal to
administer grazing. This equals a loss of of $32 million.
Few people hold most of these permits = welfare for rich
cattlemen.
Forests and Forest Products
The amount of fuel wood consumed by each person in
developing countries is roughly equal to that used as
paper products by each American.
Demand for fuel wood will be twice the available
supply in just 25 years.
The Rates of Deforestation Are Increasing
Consider Costa Rica, an environmental success story.
Lost 75% of its primary forests in the last 60 years due to
timber harvest, Del-Monte plantations, cattle grazing
(mostly for export).
Costa Rica (the “Green Republic”)
Costa Rica contains more biological diversity than all
of North America combined.
Costa Rica encompasses only.03%
of the world’s landmass, but it
contains and supports 5-6% of the
entire world’s biodiversity.
Costa Rica Policies
Costa Rican Government has been a front runner in
conservation policy - 90% of its remaining forest is
protected, and it has the largest percentage of land
dedicated to national parks in the world.
Emphasis has been on sustainability.
Along with a strong conservation policy, the Costa
Rican Government has enacted incentive programs to
promote reforestation projects. These incentive
programs include such things as residency status and
various tax exemptions.
Causes of Tropical Rainforest Destruction
Commercial Logging: tropical forests harvested for
timber.
Subsistence agriculture: “slash and burn tactics” (also
called swidden or milpa agriculture).
Cattle ranching: After commercial harvesting or after
subsistence agriculture, or on its own.
“Slash and Burn” (Swidden or Milpa
Agriculture.
Farmers clear a small plot (2 acres), burn the dried plants
to provide a burst of nutrients (and ash is basic,
increasing the release of minerals from clay).
On field, they practice polyculture (using some
perennials). Banana/plantain, papayas, cassava and sweet
potato (root crops), beans (increase nitrogen), and maize
(plots hold the soil because there is a variety of roots).
In time, the plot is given over to encroaching forest
because the fertility has decreased, and the farm begins in
a new area.
Milpa Agriculture
Depends on land to rotate
through. If the farm remains
long term, the productivity
of the land declines.
Higher populations are
increasing the pressure on the
land and not allowing enough
time for recovery.
Cattle Ranching
Ranching often introduced after commercial harvesting or
after subsistence agriculture, or on its own.
Tropical soils are Oxisols and
ultisols - soils that are highly
leached and nutrient poor.
Minerals are locked up in the
vegetation; if vegetation is lost,
minerals are lost.
So, it is hard to go from a pasture
back to a forest again.
Logging in the
U.S.A.
Kinds of cutting:
Clear cutting: removal of all wood in a compartment.
Strip cutting: harvesting strips within a compartment on a
rotational basis.
Selective cutting: planned removal of individual trees or
small groups of trees within a forest stand.
Clear Cutting:
Cost effective because large machines can be used, making
it easier to fell, trim and skid logs.
But: 1. Eliminates almost all habitat
2. Increases soil erosion greatly
3. Favors early succession tree species and deer (game)
4. Increases soil and water temperatures.
Sometimes seed trees or nurse plants left
Clear Cutting:
Clear Cutting:
Strip Cutting
1. Reduces erosion compared to clear cutting
2. Provides seed sources for establishment,
But strip
cutting still
favors early
successional
tree species
and edge
animals.
Selective Cutting
• Favors the more shade-tolerant trees like red spruce,
sugar maple and hemlock because the shade is not
broken.
2. Provides a continuing supply of food and cover for
wildlife throughout the life of the forest.
3. An uneven-aged stand is particularly favorable to birds.
Selective Cutting
Need intensive skilled management to prevent degradation
of the remaining stand (genetically superior trees are likely
to be removed).
Management and skidding costs are likely to be higher,
road construction and maintenance must be more
extensive.
High grading - taking out
the few choice trees for
profit and leaving the rest.
Lowest impact, but
requires other skidding
techniques.