The answers here are probably more detailed than we would expect you to have included in your answers, but we want to take another stab at helping you understand these ideas.
Please use the "Talk to Ed and Mike" forum in Moodle if you wish to discuss the assignment further.
Completion of questions 1 and 2 will help you achieve Objective #3 for lecture #2.
Question
#1 (5 points)
What would happen to the climate and vegetation of Champaign-Urbana if the tilt of the earth were some how changed from 23.5 degrees to 12 degrees? (The Earth's axis would be tilted about half as much as it is now).
As part of your explanation address these questions:
HOW and WHY would the following factors change (or not), compared to what we normally experience, because of such a change in the tilt of the earth's axis.
a1. The distance of Champaign-Urbana from the sun
a2. The angle of incidence of sunlight during the different seasons of the year
a3. The length of the day during the different seasons of the year
a4. The average temperature during the different seasons of the year
a5. The location of the Tropics of Cancer and Capricorn
a6. The location of the Arctic and Antarctic Circles
a7. What new challenges would the plants and animals that live in central Illinois face as a result of such a change in the tilt of the earth's axis?
Additional Resources for question 1, part a:
Question 1, Answer
Seasons in Champaign Urbana occur primarily because of the 23.5 degree tilt of the earth. The amount of solar radiation per unit area changes with the angle of the sun at any given time of the year in areas north or south of the tropical zones. Try the 5 question Survey. During winter in the Northern Hemisphere the earth's North Pole is pointed away from the sun causing the sun to appear low in the southern sky. The sunlight energy per unit area is less than in the summer when the north pole is pointing towards the sun causing the sun to appear higher in the southern sky. It is the amount of solar energy per unit area, because of the angle of incidence of the sun's rays at different times of the year, that affects the heating of the surface of the earth and the subsequent heating of the air.
The variation in seasonal climate extremes is in part determined by the distance from the equator (north or south) of the position being considered. If a position on the earth is far from the equator the sun will be lower in the sky during the winter, the mid-winter nights will be very long, and it will be very cold. The summer days will be longer in mid-summer, though the sun will still be low in the sky and solar energy per unit area will be low. If a position on the earth is close to the equator, the sun will be high in the sky all year, there will be high solar heating per unit area, and there will be little temperature or day length variation throughout the year.
On the longest day of the year for us in the Northern Hemisphere the sun is directly overhead at the tropic of Cancer at 23.5 degrees north of the equator. The longest day of the year for us in the northern hemisphere would look like the illustration of the earth to the right in this image. On our shortest day the sun is directly overhead at the tropic of Capricorn at 23.5 degrees south of the equator. Looking to the north, on the longest day of the year for us the sun never sets north of the Arctic Circle which is 23.5 degrees south of the North Pole. In our winter on the shortest day of the year the sun doesn't come up at all north of the Arctic Circle. The reverse is true for the Antarctic Circle in the Southern Hemisphere which is 23.5 degrees north of the south pole.
Seasons are the result of the 23 1/2 degree tilt of the earth's axis and the resulting variation in solar radiation per unit area. It is not because of the relative distance of the earth from the sun in its orbit at different times of the year. If you said that, you got the question wrong.
OK, that's the basic information you need to understand about seasons to answer the questions about what would happen if the tilt of the Earth's axis were decreased to 12 degrees.
The distance of Champaign-Urbana from the sun would not significantly change.
The angle of incidence of sunlight during the different seasons of the year - On the longest summer day of the year the sun would be lower in the sky than it is normally, so the angle of incidence would be more slanted, spreading the energy over a larger surface area. On the shortest winter day the sun would be higher in the sky than it is normally, resulting in less heating.
The length of the day during the different seasons of the year - The longest summer day would be shorter than it is normally. The shortest winter day would be longer than it is normally.
The average temperature during the different seasons of the year - Because the sun is lower in the sky in the summer, there would be less solar heating and cooler summers. The more direct rays of the sun in the winter would produce warmer winters.
The location of the Tropics of Cancer and Capricorn - On the northern hemisphere summer solstice the sun would be directly overhead at 12 degrees north. On our winter solstice the sun would be directly overhead at 12 degrees south.
The location of the Arctic and Antarctic Circles - The Arctic Circle would be located 12 degrees south of the North Pole [78 degrees north] rather than 66.5 degrees. The Antarctic Circle would be located at 78 degrees south. The circular area of continuous darkness in the winter and continuous light in the summer would be smaller.
Plants and Animals - Organisms native to our area or that migrate through here have evolved and adapted to the current seasonal conditions of day length and temperature. The cooler summers and warmer winters may not be suitable for some of the species. Many animals and plants respond to specific seasonal changes in temperature and/or day length to change their development and/or behavior. Some species may be able to survive only further north or south. Other species may find the new environmental conditions suitable and move into our area.
Question #2 (5 points)
The state of Montana is located in the Northwest part of the United States between 44 degrees, 21 minutes and 49 degrees North latitude. A major biome type in western Montana is montane forest, where the annual rainfall varies from 40 to over 80 inches in some places. The eastern part of the state experiences a very low rainfall, less than 15 inches annually in some places, creating dry grassland conditions.
Explain why there is a montane forest in Western Montana and dry conditions in Eastern Montana.
As part of your explanation, address these questions:
b1. How do the Rocky Mountains affect the temperature and relative humidity of the air flowing across them?
b2. How does a change in the altitude of an air mass affect the ability of the air to hold moisture?
b3. Why is there a montane forest in the western part of Montana along the western slopes of the Rocky Mountains?
b4. Why is there a dry grassland in the eastern part of Montana east of the Rocky Mountains?
b5. Refer to the NASA image of South America and the map of South America below to answer these 2 questions:
Explain why there is a forest on the EASTERN slopes of the Andes mountains and a desert on the WESTERN Slopes of the mountains in Peru
Explain why there is a forest on the WESTERN slopes of the Andes mountains and a desert on the EASTERN Slopes of the mountains in central Chile.
Additional Resources for question #2:
Mountains
and rain shadow in the American North.
Parts b1 - b4
Forests on the windward sides of mountain ranges are associated with rising air masses. Deserts on the leeward side of mountain ranges are associated with descending (falling) air masses.
When the prevailing winds from the west encounter the mountain range in the Western part of Washington, the air mass is forced up the slopes of the mountains. As air rises into the upper levels of the atmosphere where the air pressure is much less, it cools. Because cool air can hold less moisture than warm air, the moisture in the air condenses and produces clouds and rain, providing adequate moisture to support a montaine forest community on the windward side of the mountain range.
As an air mass clears the mountain tops it slips down the leeward
slopes by gravity. As air masses descend from higher altitudes to the
lower altitudes, they heat as they are compressed in the lower
atmosphere. Since warmer air can contain more moisture than cool air,
the relative humidity is very low, preventing the formation of clouds
and causing moisture to evaporate into the air from the soil, plants,
and animals. (This is why you turn on the heating element of your hair
dryer to dry your hair more quickly.) The result is a desert
environment on the leeward side of the mountain range. In this case the
region east of the mountains is an arid area.
Part b5
In Peru, about 10 degrees south, the prevailing winds blow from east to west. Because of this difference in prevailing wind direction, the pattern of forest and desert in relation to the mountains is reversed compared to Montana.
In Central Chile, about 40 degrees south, the prevailing winds blow from west to east. Because of this difference in prevailing wind direction, the pattern of forest and desert in relation to the mountains is similar to that of Montana.
Here is a similar situation of rising and falling air masses involving different latitudes
Along the equator the sun is nearly directly overhead all the time. The angle of incidence of sunlight is nearly vertical so that the energy is high per unit area. The land surface absorbs this energy and re-radiates it as heat. When air is heated by the re-radiation of the sun's energy from the surface, it expands, becomes less dense (like a hot air balloon), and rises. As it rises the pressure decreases in the upper atmosphere and the air cools further. As the air cools, the relative humidity increases, because cool air can hold less moisture than warm air. When relative humidity reaches 100%, clouds form and rain falls on the tropical rain forest.
When the air mass reaches the upper limits of the atmosphere it flows north and south and gets plunged downward about 30 degrees north or south when it meets other air masses flowing in the opposite direction. This descending air is dry, partly because it has lost its moisture on the way up in the first place, but as it falls, the pressure increases causing the temperature to increase. As the temperature increases, it becomes even drier in terms of relative humidity. That sucks the air out of the ground, the plants, and the animals and you have a desert.
Here is a diagram of global air circulation that might help.
Completion of this question will help you achieve most of the objectives for lecture #3.
Question #3 (10 points)
On May 18, 1980 Mt St. Helens erupted, spewing a huge amount of ash, pumice, and poisonous gas as part of a violent explosion that literally blew off the top of the mountain. Some areas in the blast zone were buried deeply in ash and pumice. In other areas trees were blown down by the blast, but got a light coating of material from the blast, and still other areas experienced only slight damage and little ash deposit. Succession has proceeded at different rates in these different areas since 1980.
Look at the pre-eruption photo and the series of 3 pictures linked below and answer the following questions.
a. Based on this picture of the old-growth forest before the eruption, Picture your self the size of a mouse describe the physical environment in the Old-growth forests of Douglas fir, Pacific silver fir and mountain hemlock prior to the 1980 eruption. (temperature, humidity, sunlight, and exposure to wind and rain)
Observe these 3 photos and answer questions 2 b-d.
Vegetation
near volcano
one year after the 1980 Eruption.
This area was located on the edge of the blast zone.
Because of the lower blast temperature and reduced force of the blast,
many
trees were blown down, some trees were killed but left standing, and
some plants did survive. The deposition of ash was relatively
light in this area so the soil was not deeply covered with inorganic
material.
b. Based on the first picture taken one year after the eruption, describe the physical environment at the exposed surface of what was the forest floor at this site following the eruption. Again, picture your self the size of a mouse and describe the temperature, humidity, sunlight, and exposure to wind and rain that you would experience.
c. Finally, from the mouse perspective, describe the changes in the physical environment (soil, temperature, sunlight, rain, humidity, wind, etc.) brought on by the establishment of pioneer vegetation during the next 24 years? (pictures 2 and 3).
d. Would this particular situation be an example of primary or secondary succession? EXPLAIN the differences between the two as part of your answer.
Additional Resources for question #3:
In order to answer these questions you need to place yourself in each of the different successional times illustrated in the photos. Ask yourself what it would be like to be the size of small furry animal on the ground in each situation.
Part a. Answer
Before the eruption the Old-growth forests of Douglas fir, Pacific silver fir and mountain hemlock provided a cool, moist, shady environment. The trees provided shade for plants and animals living on the forest floor. The trees intercepted the rain which prevented rapid erosion. The decaying organic matter in the soil and the covering of mosses, lichens, and small plants soaked up the water and held it like a sponge, so water erosion was minimal. The trees and other plants sucked water up from the soil and evaporated it into the air, maintaining a high relative humidity. The dense forest growth blocked the winds, so wind erosion was minimal.
Part b. Answer
After the eruption, the trees were blownd down to the ground, but only a light sprinkling of volcanic ash fell on the remaining soil. The organic topsoil was only lightly covered by volcanic deposits. When the sun shines, it is very hot because there is no shade. When it is dark the soil cools rapidly. When it does not rain the soil becomes very dry and the humidity in the air is also low. When it rains the soil is quickly saturated and erosion washes it away. The denuded mountain side is subject to high winds. Environmental conditions are harsh and variable.
Part c. Answer
For the first several years it appears that little plant life manages to become established. However, after 9 years, the seeds and spores of pioneer plants sprouted from protected pockets under plant debris, were blown in by the wind, or carried by animals or water and started to sprout and send out roots and fibers through the soil. The interesting thing is that the harsh conditions are actually necessary for these particular pioneer plants to start growing and become established.
As these small plants become
established, they provide shade that changes the temperature and they
evaporate water that increases the humidity at the surface.
The pioneer plants provide shade that is necessary for some tree seeds
to sprout and
become established. As
generations of plants live and die, additional organic matter is added
to the soil. As more
and more organic matter builds up, larger and larger plants can become
established and further change the environment. After 24 years
the beginning of a new forest has become established.
To visualize the changes in the physical environment during this process, think about what it feels like on the pavement at Wall-Mart compared to the environment in a field of grass. The difference in the environment is caused by the plants. The plants and their roots soften the fall of rain drops and keep the soil from washing away. The plants and the dead litter that comes from them helps retain moisture in the soil. The shade of the pioneer plants cools the soil and slows the germination of seeds that require light. The plants grow upward as well, and extract water from the soil and evaporate it into the air, increasing humidity.
The seeds and spores of the pioneer plants NEED the wide open, harsh conditions of the bare mineral substrate to germinate and become established. Their seeds and spores can not germinate in conditions where other plants (even of their own species) have already become established. However, the seeds of the next community in the succession require the conditions produced by the pioneer plants, to germinate and become established. Then they change the environment in different ways. And so on and so on until you get a climax community established that can remain fairly stable until the next disturbance.
A climax community is sort of the end of the successional process. I say "sort of" because there will always be another disturbance and the successional process will start all over again. There is never really an end.
The climax community consists of a collection of plants that can live together as a community and, most importantly, can reproduce themselves in that environment. During succession there is a "succession" of communities consisting of plants that can germinate and start to grow in the conditions they find when their seeds arrive. As the plants grow and mature, they change the environment in such ways that their own seeds can not become established at their "feet", but a new set of plants find the conditions just what they need to become established.
"The only thing constant is change."
Part d. Answer
This would be an example of SECONDARY succession. The main point is that we are beginning the process WITH ORGANIC SOIL. The soil was not removed by erosion or deeply buried in rock and ash.
Not all areas around Mt. St. Helens were affected in the samy way as this site. Some ares were deeply buried in volcanic rock. In some places the trees were blown down, but the soil was protected by a layer of snow. In other places the trees were killed, but not blown down.
Use this link to see photos of other areas around Mt. St. Helens where succession was much more rapid or much slower than what you are seeing in this particular site.
