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59 Cards in this Set

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  • Back
Natural capital:
2) Ecosystem services:
the range of natural resources provided by ecosystems, such as the air, water, soil, nutrients, forests, grasslands, etc., that are drawn upon by humans as essential resources. 2)Processes by which the environment produces resources
such as air, water, timber or fish.
Renewable and non-renewable resources: *
Relationship between resource supply and consumption rates that allow for sustainable resource use
Ex. Timber versus land or coal 2) (Consumption ≤ Supply)
Forest Reserve Act –
Development of National Forest in response to over-exploitation of forest resources. This legislation conferred power on the president to remove land from the public domain, thereby enabling the forests to be preserved.
Cause of dust bowl. . .
Drought. . .
Shift in distribution of agriculture in US over the past century.
- Homestead Act of 1862 offering free public land to actual settlers.
How has the human population increased over the past two centuries?
- Times six; from 1 billion in 1820 AD to over 6 billion in 1999
What is the primary cause of the dramatic increase in the growth rate of the human population over the past century?
Increase in life expectancy. Hygiene and nutrition; medicine not until later.
What is responsible for the decline in the population growth rate since the 1960s?
The world population growth rate rose from about 1.5 percent per year from 1950-51 to a peak of over 2 percent in the early 1960s due to reductions in mortality. Growth rates thereafter started to decline due to rising age at
marriage as well as increasing availability and use of effective contraceptive methods. Note that changes in population growth have not always been steady. A dip in the growth rate from 1959-1960, for instance, was due to the Great Leap Forward in China. During that time, both natural disasters and decreased agricultural output in the wake of massive social reorganization caused China's
death rate to rise sharply and its fertility rate to fall by almost half.
What is a life table?
Table of age specific survivorship (or mortality).
How would the effect of a change in the mortality rates on population growth rate differ between pre-reproductive and post-reproductive age classes in a population? (children vs. old folks)
- Greatest effect on population growth when children versus the elderly survive as they have more reproductive years left.
How has life expectancy changed over the past 150 years? For infants? For older individuals (>40)?
- Increased; the highest is at age 70 which remained steadily at 80 since 1850. Then at age 40 which increased from under 70 to 78. Finally at birth increased from under 40 in 1850 to 75.
How have fecundity rates (number of children per female) changed over the past century?
- Decreased in all regions of the world; from 3.5 children per woman to 1.5 (at or below 2.1 in nearly all MEDCs.
Demographic transition
- Birth rate minus Death rate. High birth rate was offset by high death rate. Then decline in death rate due to sanitation and medicine but birth rate still high. Then birth rate decreased and less difference between birth and death rates. LEDCs had population negative rates and the transition happened later.
How is population growth related to (correlated with) economic growth?
- Wealthier countries with higher GDPs have fewer children with higher life expectancies.
macro- and miconutrients:
Some sixteen elements are known to be required for plant growth. These essential elements are classified as either macro- or micronutrients. The classification refers to the quantities of the element required for plant growth and does not signify importance in terms of key plant processes.
Of the macronutrients, C, H and O form the majority of plant tissues. These elements are derived from CO2 and H2O and are made available to the plant as simple sugars through the process of photosynthesis. The remaining six macronutrients exist in a variety of states in the soil and their availability to plants is affected by several important and different processes
Components of a biogeochemical cycle: inputs, internal cycling, outputs
- Plants require nutrients in mineral (inorganic form, not in living matter). These nutrients are absorbed through the roots and transported to the areas of
the plant where they are needed.
Plants require nutrients in mineral (not organic) form
[Organic nutrients: litterfall – dead organic matter – then decomposition and net mineralization; Mineral nutrients: uptake of mineral nutrients from soil and incorporation into plant tissues.]
As leaves senesce, a large portion
of the nutrient that they contain are reabsorbed back into the plant in a
process called retranslocation.
As dead organic matter is consumed by decomposers, nutrients are transformed from an organic to an inorganic (or mineral) form in a process called mineralization
: If the dead organic matter does not provide sufficient nutrients for the decomposers, they will take-up mineral nutrients from the soil.
net mineralization:
The difference between the rates of mineralization and
immobilization is called the net mineralization rate. This is
the rate at which nutrients become available for the uptake
by plants. Ex. Fungi and bacteria mineralized into the soil from dead organic matter.
Litterbag experiments:
2) Interpretation of graphs relating: % original mass remaining as a function of time
The dead plant material (litter) provides both a source of energy and nutrients to the decomposers. Therefore, the process of decomposition and nutrient release will be a function of the quality of the litter as a food source for decomposers.
- Experiments provide the absolute carbon content given a initial litter mass, ex. Beginning with 48% of total mass and ending with 25% a year later.
Changes in carbon and nitrogen with decomposition (litterbag experiments)
- Total carbon remaining after decomposition: decreases from 48% of total mass and ending with 25% a year later. *Initial increase in nitrogen due to immobilization (The level of immobilization will be a function of the initial nutrient content of the dead plant material), then decrease.
- Nitrogen levels remain steady after 100 days (slight initial increase as net release of N begins); mass of organic matter decreases; percent of decomposer mass of the remaining organic matter increases slightly from 0 to 20%. - Experiments provide the absolute carbon content given a initial litter mass, ex. Beginning with 48% of total mass and ending with 25% a year later.
As carbon is consumed and nitrogen is immobilized, the amount of carbon
relative to nitrogen declines (decreasing C:N ratio). Carbon then begins to be the limiting resource and mineralization begins to dominate over immobilization, resulting in a net release of nitrogen to the soil.
What processes are responsible for the changes in nitrogen content of litter during decomposition?
humus and soil organic matter
As plant material becomes fragmented and decomposes it forms a dark organic material called humus. This material is composed primarily of lignin compounds and is high in nutrient concentration. As a result of its poor
carbon quality it decomposes very slowly. It is an important source of nutrients which are released very slowly into the soil for plant uptake.
Major inputs and outputs in biogeochemical cycles
Inputs: Precipitation, atmospheric sources of nutrients; release of nutrients into soil through weathering of rocks and minerals.
Outputs: Volatilization from fire and loss to atmosphere. Surface runoff into surface water. Leaching into groundwater.
How does fire influence short-term patterns of nutrient availability and primary productivity? Long-term?
Increases in above ground net primary productivity (Mt/ha/yr) for a number of prairie sites following fire.
More minerals but less total N. Greater proportion inorganic N versus organic. Only beneficial in short term.
Two types of biogeochemical cycles
GASEOUS CYCLE: Atmospheric sources of nutrients.
SEDIMENTARY CYCLE: Release of nutrients into soil through weathering of rocks and minerals.
Major inputs of nitrogen to ecosystems
- N and Oxygen form nitrates coming as rainwater in form of nitric acid.
High energy fixation by lightning. N2 and oxygen combine to form nitrates which come to the surface as rainwater in the form of nitric acid. Accounts for approximately 10% of total annual N-fixation.
- Fixation of bacteria accounts for 90% each year; mutualistic association.
- Diagram with years since glaciers and stands of plants: first group does not need N in soil because they can use N gas via bacteria but then other species were able to come in leading to decline of first group; only an early colonizer. More litter; N in soil builds up because of first group (Adler) and mutualistic association. Not all plants have mutualistic associations with bacteria: legume gains no additional benefits but has costs: energy for growing bacteria.
Rhizobium bacteria and mutualistic relationship with plants
Rhizobium bacteria associated with the root system of
Legumes are responsible for 90% of fixed nitrogen
contributed to the terrestrial environment each year.
These bacteria infect the root system and form
nodules. Together with the plant, these organisms form
a mutualistic association where the bacteria provide the
plant with nitrogen while the plant provides the bacteria
with a source of carbon (energy).
The mutualistic association with Rhizobium bacteria...
has a cost to Legumes; that
cost is carbon which is produced in the process of photosynthesis. The carbon
that is provided to the bacteria would otherwise go to plant growth. Under
conditions of low nitrogen availability, the cost is essential to providing access to
nitrogen needed for plant growth. However, under conditions of high nitrogen
availability, there is little advantage, yet the cost remains.
cations and anions (NH4+ and NO3-)
Because soils have a much greater capacity to bind (hold)
cations than anions, mineral nutrients in the form of anions,
such as nitrates (NO3-) and phosphates (PO4 3-) are more
easily leached and lost from the soil than are cations (NH4
Once in soil solution, the cations can be taken up by plants
or leached from the soil to the surface and groundwater.
Ion exchange in soils
The edges of clay particles and organic matter carry a negative charge. These sites attract and bond positively charged particles (cations), such as the macronutrients calcium, magnesium, potassium, hydrogen and ammonium (nitrogen). These cations are in a state of constant flux, exchanging between the negatively charged sites and the soil solution. This process is called ion exchange.
Rotation (in forest management)
Forest management occurs over a cycle of decisions and events called a rotation. The most important steps in the rotation include taking an inventory of the site, developing a forest management plan, building roads into the site, preparing the site for harvest, harvesting timber, and regenerating and managing the site for the next harvest.
See graph; short rotation followed by short-term quality growth. Long rotation with period for long-term quality growth. Peak: maximum yield; decline: old growth harvest (such as hardwoods for furniture).
What are the following forest management /forest harvest methods?
1) No Follow-Up Management Large-Scale
(Abandon) Small-scale
2) Plantation
Possible Follow-Up Site Management
Bulldoze and pile remaining plant materials
Replant seedlings for next harvest
Burning of remaining material functions to clear the site and release nutrients
from organic material. Herbicide treatment stops the growth of grasses and
other herbs that will compete with the newly planted seedlings.
Seed tree cut
Leaves approximately 5% of trees as a source of seed for natural regeneration.
No Follow-Up Management
This management approach is typically used for single-species forests with species that regenerate (reproduce) very easily. Often applied in boreal forests.
Selective cut
Individual trees of commercially valuable species
(High-Grading) are selectively removed, leaving the remainder of
the forest largely undisturbed.
No Follow-Up Management
This management approach is used in hardwood forests in the temperate and
tropical regions. Trees that are selected are usually of commercially valuable species used for lumber (e.g., Oak, Cherry, Mahogany).
Although producing a minimum impact on the ecosystem, this practice can
have a large impact on the patterns of species composition and diversity of
the forest.
Effects of tree cutting...
- Disruption of Nutrient/Nitrogen cycle. Mining nutrients. Temperature of soil surface increases and hence rate of decomposition increases.
- Greater forest floor organic matter after initial decline following clear cut.
- Other species with mutualistic association colonize.
- N production for tree harvest/clear cut versus no harvest (little N produced; slow decomposition) and N production.
Effects of tree cutting...
Clear cut watershed versus uncut in terms of nitrate: In streams versus soil. More lost initially. Net effect: decreases nutrients; influences internal cycling of nutrients. More solar radiation if less plants. Productivity increases for decomposing and mineralizing. Little demand for nutrients however (no plants). Despite initial spike, still decreases. Direct loss of wood, etc; loss of nutrient cycle.
How does forest clearing/harvest disrupt nutrient cycling in the ecosystem?
Rate of decomposition
Decline in forest-floor organic matter following clear-cut at Hubbard Brook Experimental Forest (New Hampshire). The decline is a direct function of the increased rate of decomposition resulting from increased soil temperature following the removal of the forest canopy. The stabilization and subsequent rise are a result of the recovery and regrowth of plants.
As the vegetation begins to recover, soil temperatures decline, litter and soil organic matter begins to accumulate, and some nitrogen is replaced by Legumes that colonize the area following the disturbance.
Seed tree cut (along with patch cut and clear cut)...
has reduced rate of decomposition and mineralization. Seed-tree has the most original mass remaining, followed by path and clear; seed however has the lowest mineralized nitrogen content.
--Leaching of nutrients from soil. . .?
How do the three forest harvest methods listed above differ in their impact on the ecosystem (particularly on the cycling of nutrients)?
Sustainable yield:
Yield: quantity of resource harvested
2) yield per unit time is equal to the productivity per unit time
Consumption = Regeneration

As nutrients are removed from the forest ecosystem, productivity declines
and the period of time required for the forest resource(s) to achieve a
given yield will increase (increased rotation time).
If the rotation time is maintained...
2) Inputs:
then yield will decline with time:
2) Natural and fertilizers => Ecosystem (internal cycling) => Outputs: harvest and natural outputs.
Total global agricultural production has increased to meet growing population demand as a function of two factors described by the following equation:
Total production = acres in production x production per acre
Increased production per acre has been a product of a variety of practices influencing...
irrigation, fertilization, pesticides and crop improvement.
Contrast: Traditional/subsistence agriculture and High technology agriculture
U.S. Corn Production
1) Much higher net primary productivity
(addition of fertilizers and sometimes irrigation)
2) Patterns of carbon allocation very different (No natural cycling of nutrients such as decomposition).
Prairie: Allocation to roots to survive drought and promote regrowth following fire and grazing
Corn: Large allocation to reproduction
U.S. Corn Production
3) Complete removal of plant residues (bare soil) results in the reduction of organic matter inputs and long-term reduction in soil organic matter.
4) Loss of soil through erosion.
Large commercial farms are highly productive, but at the cost
of large inputs of chemical fertilizers and severe soil loss.
- N removed esp in corn versus rice and wheat. Percipation as compensation along with fertilizer. Costly Fertilizer lost as runoff.
What are the consequences of high technology agricultural practices (such as corn production)?
* Increased soil losses and therefore Unsustainable without continuous input. Ex. Fertilizer.
- US has lower return and is not energy efficient (diminishing returns).
[Loss of nutrients from agricultural ecosystems through crop harvest] Soil erosion:
Most soil loss for continuous cotton, up and down hill and least for no-till and contour; followed by corn-wheat-hay-hay-hay.
What are the stages of slash and burn agriculture?
1) Area cleared. 2) Pyrominerlization (into ash with high mineral content functioning as fertilizer). 3) Fallow period for regrowth and nutrient cycling. 4) Regenerating forest. 5) Overall N lost but redistribution.
See graph: Yield decreases every year and after about three years is abandoned. No added chemical fertilizer in general, no input. Plots may be used for one year, then let internal nutrient cycle begin and recovers after 16 years. Given wasted years, low productivity.
How does fire influence the short-term (growing season) availability of mineral nutrients?
Recall from our earlier discussion that although fire results in a short-term increase in available mineral nutrients, there is a net loss of nutrients from the ecosystem.
What process allows the nutrient status of areas used for slash and burn agriculture to recover to initial (pre-clearing) levels?
Changes in nitrogen storage over the full cycle (16 years) of a shifting cultivation system in the humid tropics (recovers but after 16 years).
What are the advantages and disadvantage of slash and burn agriculture?
Shifting cultivation (slash and burn) in the humid tropics.
Declines in yield are a direct result of declining nutrients.
Slash and Burn (Shifting) Agriculture
Advantages: No fertilizer input
Forest allowed to recover after 3-5 years. This period allows for the recovery of nutrients and soil organic matter.
Disadvantages: Declining productivity in successive years.
Low productivity per unit land area because of long
recovery period*.
[Synthetic nitrogen fertilizer now supplies...]
about half of the
nitrogen used annually by the world’s crops. At least onethird
of the protein in the current global food supply is
derived from the synthesis of ammonia (NH3) from
hydrogen and nitrogen using the Haber-Bosch process.]
Runoff from agricultural lands is responsible for large inputs of
sediments and nutrients to streams and rivers.
The large inputs of nutrients to freshwater ecosystems from
agricultural runoff has led to the problem of eutrophication.
Eutrophication: nutrient enrichment of a body of water.

--Chemical contamination of wells is a notable problem for
humans, with nitrate fertilizers being the most common pollutant.]]
Input of nutrients from managed systems increases productivity of surface waters
The high productivity results in a large input of dead
organic matter to decomposers (primarily bacteria) (Increased oxygen uptake by decomposers). The large input of dead organic matter to decomposers (primarily bacteria) results in high decomposer respiration rates, dramatically reducing oxygen levels in the water. The high nutrient concentrations and low oxygen levels can result in fish kills and a general reduction in animal life.
(Reduced oxygen availability for fish).
In the 1970’s, corals dominated Jamaica’s
reef ecosystems; 20 years later, algae has
taken over these same areas. (b) Algae
growing on soft corals.