Transcript Document

Module 9:
The Effects of Elevation on Forest
Microclimate,Flora and Insect Life
SEE-U 2001 Biosphere 2 Center, AZ
Yuko Chitani
Adam Nix
Professor Tim Kittel,
Mei Ying Lai
Eli Pristoop
TA Erika Geiger
Lily Liew
J.C. Sylvan
Asma Madad
Introduction
Introduction:
In this exercise, we studied how climatic factors
and biodiversity change with increasing elevation
gradients at Mount Lemmon. We measured climatic
factors such as temperature, relative humidity, wind
speed, and pressure. We also obtained local weather
records to evaluate precipitation, We also studied
changes in biodiversity by sampling the plant and
insect species found along the various gradients.
As elevation increases, abiotic factors such as
temperature and light also change. Temperatures tend
to decrease as elevation increases, and plants must
adapt to both changing elevation and temperatures.
According to Humboldt’s Rule, plant communities
change with altitude and temperature (Danoff-Burg,
Module 9). Some plants will adapt better to the
decreasing temperatures found at higher elevations
than other plants.
In addition, when the aspect of a slope changes, the amount of
solar radiation also changes. The difference in amount of light
influences the plant species found at each site.
Insects depend on certain plants to survive, and if those plants
are able to adapt to a particular elevation, species of insects which
depend on these plants will similarly be found at these elevations.
By analyzing plant and insect samples collected at four varying
gradients on Mount Lemmon, we can attempt to answer these
questions:
What is the general climatic trend as we move along an
elevation gradient?
How do plant and insect species respond to changing light and
temperature found at increasing elevations?
At which elevation is the greatest species richness?
Figure 1: Relationship Between Latitude and Altitude
Relationship between latitude and altitude, copyright 1990, Wadsworth Inc.
8500 ft (4)
7840 ft (2)
7600 ft (3)
4380 ft (1)
Figure from
Reading the
Landscae of
America
Mary
Theilgaard
Watts
Methods
Since our main objective was to test the factors that change along an
elevation gradient, such as moisture, precipitation, solar radiation, temperature,
soil, etc., we controlled the elevation by laying out an elevation transect. We
tested four elevations in total:
Site One: Molino Basin – 4380 ft. / 1335 m.
Site Two: Bear Wallows – 7840 ft. / 2280 m.
Site Three: Marshall Gulch – 7600 ft. / 2316 m.
Site Four: Mt. Lemmon – 8500 ft. / 2591 m.
We laid out a 25-meter transect line in all the sites, except for Site One. In
Site One, we laid out two 25-meter lines. We laid the first one to test the
chaparral community and the second one to test the oak woodland community.
Before laying out these lines, however, there were few factors that we decided
to uniformly test in all four sites. These factors were:
General site description – As a group, we decided on distinct features of each
site.
Elevation (in ft.) – We utilized both the topographic map and the GPS. In both
Site One and Three, the two readings did not correspond. We chose the
topographic map reading over the GPS because we knew precisely where we
were on the map and the GPS probably encountered difficulties in tracking
enough satellites to provide accurate readings for elevation.
Latitude/Longitude – We recorded the readings from the GPS. The GPS
appears more accurate in determining horizontal location than vertical location.
Maximum/Minimum temperatures (C) – Our tireless Professor Tim and TA
Erika strapped thermometers along all four site locations 3 days before our
experiments in order to map the change in temperature across these sites.
Relative humidity (%) – We measured the moisture content in the air by using
a sling psychrometer.
Wind speed (km/hr) – Using an instrument called the anemometer, which
operates on Bernoulli’s principle, we measured the wind speed across all four
sites.
Atmospheric Pressure (in. Hg) – We used a barometer to measure
this and also to estimate the altitude.
Slope angle – We estimated the slope angles by using trigonometric
functions.
Aspect – We used a compass and measured a down-slope line
perpendicular to the transect line. Unfortunately, we were not able to
measure the slope angle and the aspect for Site One.
After these factors were determined in each site, we laid out the
transect lines. We then determined species richness, not percent
cover, along the lines. We recorded species richness for both plants
and arthropods.
We included an additional site in our data. A pine forest site,
known as Mile 16, was included in our analysis. The data from this
additional site was collected in the year 2000. We also compared our
data with year 2000’s data done at Molino Basin, Marshall Gulch, and
Mt. Lemmon. Lastly, we included climate patterns from Tucson
airport (with an elevation of 2579ft. / 786 m.) Although we did not
measure the species richness in this area and the measurements in this
site were based on a daily average, we included this low elevation in
order to show a general climatic trend across different elevations.
Methods Cont’d
TEAMWORK
Results
Considering the possibility that vegetation might be a function of climate--as in
the equation provided by Jack Major (1951) V= f (cl, p, r, o, t)--, we took
stock species richness at four sites along a microclimatic gradient in the Santa
Catalina mountains. We measured several climatic indicators at each site
including temperature, barometric pressure, wind speed, relative humidity,
and elevation. These are our results:
Relative humidity and wind speed are directly proportional to elevation
(Figure 1, 2).
Barometric pressure and temperature are inversely proportional to
elevation (Figure 3, 4).
Plant species richness also seems to be inversely proportional to elevation;
though based on our observations, there is greater biotic productivity at the
higher (and moister) elevations (Figure 5).
Arthropod morphospecies seem to be most abundant at intermediate
elevations (Figure 5).
Soil types varied between sites—the % of organic material seems to
increase; this may not have been directly dependent on elevation.
Table of Data Results
Figure 1
Elevation vs. Relative Humidity
3000
50
45
2500
40
35
2000
30
1500
25
20
1000
15
10
500
5
0
0
Tucson Airport
Molino Basin
Marshall Gulch
Elevation (m)
Bear Wallows
R H (%)
Mt. Lemmon Summit
Figure 2
Elevation vs. Wind Speed
3000
12
2500
10
2000
8
1500
6
1000
4
500
2
0
0
Tucson Airport
Molino Basin
Marshall Gulch
Elevation (m)
Bear Wallows
Wind speed (km/hr)
Mt. Lemmon Summit
Figure 3
Elevation vs Atmospheric Pressure
3000
35
30
2500
25
2000
20
1500
15
1000
10
500
5
0
0
Tucson Airport
Molino Basin
Marshall Gulch
Elevation (m)
Bear Wallows
ATM press. (in. of Hg)
Mt. Lemmon Summit
Figure 4
Elevation vs. Tem perature
45
40
41.7
39.5
Tem perature (C)
35
30
27.5 28.0
25
20
24.0
21
19
15
14
12
11
10
5
0
760
860
960
1060
1160 1260
1360 1460
1560 1660
1760 1860
1960 2060
Elevation (m )
Max temp (degrees C)
Min temp (degrees C)
2160 2260
2360 2460
2560
Figure 5
Elevation vs. Species Richness
23
3000
20
16
2124
17
2390
2591
17
2316
2000
15
10
1335
1335
6
5
9
1500
9
7
7
3
5
2500
1000
500
0
0
0
Molino Basin
Scrub
Molino Basin
Oak Wood
Area 51
Bear Wallows Marshall Gulch
Mt. Lemmon
Elevation
Number of Species
25
Figure 6
Results Cont’d
Regionally, these sites all have the same climate. In Major’s application of Jenny’s
formula , regional climate is represented by the value r. We also created climate diagrams
based on data collected at weather stations in the vicinity of this gradient. These diagrams
illustrate the relation between average monthly precipitation, average monthly
temperature and elevation in the Santa Catalinas. Since we collected our data over the
course of one day these diagrams give us the best picture we have of the relation between
elevation and precipitation. These four sites (and by corollary our four sites) lie within the
same regional climate, thus we were able to eliminated r from this experiment. Based on
these diagrams we recognized some of the following trends:
They exhibit the same pattern in preciptation (two rainy seasons
interspersed with long dry seasons, and similar seasonal temperature
fluctutations (even if they are in different ranges.
Precipitation is directly proportional to elevation.
Temperature is inversely proportional to elevation.
USA
°C 32.18°N / 110.49°W / 805m
+0.0 SABINO CANYON, ARIZONA
+0.0 [34-34] +20.5°C 332mm
400
300
200
50
100
90
40
80
70
30
60
50
20
40
30
10
20
10
+0.0
+0.0
0
mm
Data compiled from
-10
1948-1982
U.S.A.
°C 32.60°N / 110.70°W / 1375m
+0.0 ORACLE 2 MILES SOUTHEAST
+0.0 [ ] +16.7°C 576mm
400
300
200
50
100
90
40
80
70
30
60
50
20
40
30
10
20
10
+0.0
+0.0
0
mm
Data compiled from
-10
1950-2000
U.S.A.
°C 32.60°N / 110.78°W / 1402m
+0.0 ORACLE, ARIZONA
+0.0 [ ] +16.8°C 492mm
400
300
200
50
100
90
40
80
70
30
60
50
20
40
30
10
20
10
+0.0
+0.0
-10
0
mm
Data compiled from
1893-1949
U.S.A.
°C 32.42°N / 110.72°W / 2426m
+0.0 PALISADE RESEARCH STATION
+0.0 [ ] +9.3°C 790mm
400
300
200
50
100
90
40
80
70
30
60
50
20
40
30
10
20
10
+0.0
+0.0
-10
0
mm
Data compiled from
1965-1981
Discussion
As our group rode up to the first site, we were observing the
vegetation along the Catalina Highway. At about 2,400 feet {731.52
meters} there was Velvet Mesquite, fairyduster, Arizona walnut, saguaro
cactus, Arizona sycamore, creosote bush, Fremont cottonwood, ocotillo,
barrel cacti, yellow paloverde, jumping cholla, and Arizona alder. The first
site was not that windy but it was warm and increasing in temperature by the
minute.
On the way up to the second site we observed the following vegetation
along the highway from about 3,500 feet – 5,000 feet {1066.8-1524
meters}; Saguaro Cactus, Mesquite, yellow paloverde, creosote bush,
jumping cholla, ocotillo, Arizona walnut, Arizona sycamore, Emory oak,
Mexican blue oak, Arizona white oak, gambel oak, silver leaf oak, and
alligator juniper. It was evident that with increasing elevation, changes
occurred with vegetation. From 5,000 to 6,000 feet {1524-1828.8 meters}
we observed Arizona sycamore, mesquite, gambel oak, Arizona white oak,
emory oak, ocotillo, alligator juniper, Mexican pitch pine, madrone,
ponderosa pine, and Douglas fir. From about 6,000 feet to 7,840 {1828.82390 meters} the vegetation followed the previous patterns of changing with
elevation. We observed Silver leaf Oak, Ponderosa pine, madrone, alligator
juniper, Fremont cottonwood, emory oak, Mexican blue oak, gambel oak,
Arizona walnut, white fir, aspen grove, and Douglas fir.
The third site was an area that had similar vegetation as the
second site. In fact, the elevation was 7,600{2316 meter}, and 240 feet{74
meter} below the second site. Both sites had steep slopes (that required skill
to maintain balance), and they were located close to the bottom of the slope
near the arroyos. The third site was on a northeast slope, and the second site
was on a southwestern slope. The significance in this was the amount of
solar radiation loading on a northwest slope is greater then a southwestern
slope, which affects soil temperature and evaporation rate. With this in
mind, the only major vegetation difference was that site Three had some
grass, and site Two had no grass on the forest floor.
The fourth site was at an elevation of 8,500 feet
{2591 meters}. The area had a lot of grass, and
was very cool and windy. We sampled an area just
below the top of the slope; the slope was not that
steep that people had a hard time maintaining their
balance like previous slopes.
Discussion, Cont’d
Atmospheric pressure decreases with increase in elevation.
A decrease in the number of molecules in the air above occurs with
an increase in elevation. When comparing the minimum
temperature to the maximum temperature for all the sites, a pattern
is apparent. For site One, the temperature at its maximum was 39.5,
and minimum was at 18.5 degrees Celsius. At about 3,460 feet
higher, the maximum temperature drops down to 28 and the
minimum is 13.5 degrees Celsius. At the top of the mountain the
maximum was about 24, and the minimum was 12 degrees Celsius.
Why does temperature decrease in higher elevations? The Ideal
gas law: pV=nRT, basically states that pressure times volume is
equal to the number of molecules in the air which create the
temperature. The decrease in pressure that occurs with increased
elevation means that fewer molecules are present. The decrease in
molecules in the air means that the molecules are traveling farther to
collide and this means a lower temperature. The higher the
elevation the decrease in temperature only applies to the
troposphere.
When looking at the wind speed relative to elevation, there
seems to be an increase in speed with elevation. The first site had a
wind speed of 5.5 km/hr, the second site 8 km/hr, third site 10
km/hr, and finally the forth site 11 km/hr. Why does wind speed
increase with elevation? The lower topographical areas have
mountains, trees, and hills that slow the flow of wind. However in
higher topographical regions the mountains and hills are not
blocking the wind, allowing for higher topographical areas to have
more and faster winds.
The relative humidity on site
one was 45% relative humidity, site two was
40%, site three 32%, and site four was 35%
relative humidity. Site four was higher in
elevation than site three, yet site four has a
higher level of relative humidity.
Topography influences precipitation as far as
how much precipitation that some areas
receive. As the relative humidity increases
so do the levels of precipitation. Could the
time of day affect the accuracy of these
tests? If the relative humidity were taken
at all the sites, at the same time would
another pattern develop? Because we
measure the first site early in the morning
there was the highest percent of relative
humidity. If we had measured that site again
at the end of the day there would have been a
very low percent of relative humidity. This
is because as the day goes on the climates of
certain places change, with the influential
factors such as solar radiation levels,
precipitation, wind, and temperature. As the
day went on that first site got hotter, with this
change it lowers the relative humidity level.
If we had tested all four sites at the same
time of day, the results with climate would be
more exact to illustrate a climate pattern.
Discussion, Cont’d
When analyzing the insect and plant data from all of the sites some acute patterns appear. The first site (4380 feet Oak
Woodland and Chapparal) line A, had twenty-three different species of vegetation. On the other hand, line B had fourteen different
species of vegetation. This site was important because the two different lines represented two different vegetation areas. Site one was a
transition zone from oak woodland vegetation to chaparral vegetation. There was six different species of arthropod morphotaxa from
line A. From line B there where five different species of arthropod morphotaxa. Even though these lines were not that far apart they
reflect the slight changes in vegetation and arthropod morphotaxa that occur in a transition zone.
Site two(7840 feet Ponderosa Pine/Oak Pine Woodland) had seventeen different species of vegetation. Site two also had
nine different species of arthropod morphotaxa, which is an increase of 3-4 species of arthropod morphotaxa. Site three(7600 feet Oak
Pine Woodland) which was about 240 feet {74 meters} lower then site two had 19 different species of vegetation. There where nine
different species of arthropod morphotaxa.
On site four (8500 feet Mixed Conifer Forest) the vegetation decreased to only six different species of vegetation, and seven
species of arthropod morphotaxa. On the highest elevation that we counted the number of vegetation species and arthropod morphotaxa,
there was a decrease in both. This can be attributed to the topography and the climate factors that go along with higher and lower
topography levels.
Some
possible sources of error
could have been with the
accuracy of the GPS
readings. The time of
day differed from site to
site and this could affect
the accuracy of the data,
regarding climate
patterns. For instance
the relative humidity and
temperature changed
from site to site as the
day moved on.
Conclusion
What is the general climatic trend as elevation gradient increases? How do changing climatic factors
influence biodiversity at increasing elevations? At which elevation is the greatest species diversity? In this
exercise, we learned to use several new instruments and techniques to gather climatic data:
--Sling psychrometer (measures relative humidity)
--Anemometer (measures windspeed)
--Barometer (measures atmospheric pressure and altitude)
--Trigonometric functions (measure slope angle)
--Compass to measure down a slope line perpendiular to transect (measure aspect)
From the data gathered, we learned that elevation influences climate as follows:
• Temperature decreases at increasing elevations; according to the Ideal Gas Law, less atmospheric
pressure is exerted at higher elevations so air molecules are farther apart and release less energy (i.e.
temperature) as they collide with each other.
• As elevation increases, relative humidity increases as it is a function of temperature; at cooler
temperatures, relative humidity is higher as there is more moisture in the air.
• At higher elevations, wind speed increases due to less surface roughness such as hills, mountains, and
trees to disrupt the flow of wind.
• Precipitation increases as relative humidity increases, but this is not necessarily true because at increased
elevations in tropical areas, there is a cap of subsiding air at higher elevations.
• As elevation increases, atmospheric pressure decreases due to the decreasing number of molecules in
the air column above..
- Plant species richness is inversely proportional to elevation; thus the climatic factors which are directly
proportional to elevation seem to have a limiting potential on species richness. Arthropod morphotaxa
diversity did not change much with elevation changes.
From this exercise, we learned that as elevation changes, species diversity also differs. At higher
elevations, there were more evergreens such as Douglas Fir and white fir forests, whereas at lower
elevations, there is more vegetation that grew closer to the ground, for example, cacti, grass, and forbs.
However, species abundance was greater at site one, the lowest elevation, than at the other sites.
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