Download “Lecture” Notes - Fort Hays State University

“Lecture”
Notes
Department of Biological Sciences, Fort Hays State University
Course Homepage
Instructor: Mark Eberle
Additional information that will help you to complete your study guide is included in
the descriptions of the sites we have visited on our trips (Highlights from Previous Trips). The
number of questions you will have about this information will depend on the depth of your
background in natural history. Contact the instructor ([email protected]) with all of your
questions as you read this material and complete your study guide.
Information for this on-line "lecture" and the summaries in the "Highlights from
Previous Trips" webpages was derived from the references listed below (and listed on
individual webpages), as well as from educational materials and observations at the parks and
other public sites we have visited.
Agee, J.K. 1993. Fire ecology of Pacific Northwest forests. Island Press, Washington, DC.
Alt, D.D., and D.W. Hyndman. 1975. Roadside geology of northern California. Mountain
Press Publishing Company, Missoula, Montana.
Alt, D.D., and D.W. Hyndman. 1978. Roadside geology of Oregon. Mountain Press
Publishing Company, Missoula, Montana.
Alt, D.D., and D.W. Hyndman. 1984. Roadside geology of Washington. Mountain Press
Publishing Company, Missoula, Montana.
Johnston, V.R. 1994. California forests and woodlands: a natural history. University of
California Press, Berkeley.
Lanner, R.M. 1999. Conifers of California. Cachuma Press, Los Olivos, California.
Schultz, S.T. 1990. The Northwest Coast: a natural history. Timber Press, Portland,
Oregon. (Primary source, originally used as the text for the class, but it is no
longer in print. The author referenced sources for his general explanations.)
Trudell, S. 2002. Mycorrhizas (5): fall mushrooms, ghostly fungus-robbers, and a
definition revisited. Mushroom: The Journal of Wild Mushrooming, Issue 77, Fall.
Accessed 21 June 2006 at http://www.mykoweb.com/articles/Mycorrhizas_5.html.
Wiedemann, A.M., L.R.J. Dennis, and F.H. Smith. 1999. Plants of the Oregon coastal
dunes. Oregon State University Press, Corvallis.
GEOLOGY
Geography of the Northwestern USA (see handouts)
We will travel through several physiographic provinces on our trip, and they are
labeled on the map handout. You should be familiar with the location of the physiographic
features on the map. Our focus will be on the coastal ecosystems (rain forest, tidepools, sand
dunes, and estuary), but we will also compare the communities on the various mountain
ranges that we will cross. Information on these communities is available elsewhere within this
website (Highlights from Previous Trips). What follows here is a general outline of selected
general concepts and processes.
Plate Tectonics (see handout)
The surface of the Earth is broken into several plates. Radioactive decay in the core of
the Earth creates convection currents that circulate in the molten mantle below the plates.
These currents pull the plates in various directions: moving toward each other (as along the
Pacific Northwest coast), moving away from each other (as along the mid-oceanic ridge), and
sliding past each other in opposite directions (e.g., as along the southern California coast).
Mid-oceanic ridges form where convection currents diverge at the surface; basalt is deposited
at the ridge, which pushes the adjoining plates apart (see handout).
In areas where the plates are moving toward each other, trenches (subduction zones)
form where the heavier basalt of the oceanic plate moves under the lighter materials of the
continental plate. For example, the East Pacific Plate (which is comprised of the Juan de Fuca
and Gorda plates shown on the map handout) is moving under the continental plate along the
Pacific Northwest coast north of Cape Mendocino. As the subducting plate is deflected at an
angle under the continental plate, it reaches a depth at which the high temperature and
pressure cause it to melt. This molten material then rises to the surface, where it can flow over
the surface (e.g., basalt lava flows) or solidify beneath the surface (e.g., granite batholiths) in
volcanically active areas, such as the Cascade Mountains.
The coast of a continent that is separated from a mid-oceanic ridge by oceanic crust, as
occurs along the eastern coast of North America, is known as a passive margin where erosion
dominates. The coast of a continent near the leading edge of the plate, as occurs along the
coast of the Pacific Northwest, creates an active margin where volcanic activity and accretion
dominate.
Geological Processes of Western North America (Cordillera)
Volcanism. Lava flows, cinders, and ash are examples of extrusive deposits, in which
the molten material solidifies when it reaches the surface. Cascade Mountain volcanoes are
composite volcanoes, which are built from alternating layers of flowing lava and deposits of
cinders and other airborne debris.
Batholiths (large volumes) and plutons (small volumes) are examples of intrusive
deposits, in which the molten material solidifies before reaching the surface. For example, the
granite peaks in Sierra Nevada were subsurface volcanic deposits that were later exposed by
uplift and erosion of the overlying geological materials (see handouts).
Extension and Compression. In addition to volcanic activity, the movement of the
plates and the underlying convection currents produce strains of extension and compression
on the surface that can also create mountain ranges.
Extension can cause elongated blocks of land to rise (mountain ranges) or fall
(intervening basins). These mountain ranges tend to run parallel to each other, as seen in the
north-south ranges of the Great Basin from the Sierra Nevada of eastern California to the
Wasatch Mountains of eastern Utah (see handouts).
Compression can fold and lift layers of rock into upward bulges. The Olympic
Mountains of northwestern Washington and the Coast Ranges of western Oregon and
northern California are comprised of uplifted material scraped from the surface of the oceanic
crust as it slides under the continental plate (see handouts).
General Sequence of Geological Events
1) 200-80 mybp: Pangea begins to break into northern and southern continental masses.
a) Sierra Nevada volcanic activity occurs (oceanic plate subduction).
b) Volcanic activity also occurs in the region around present-day Idaho, east of presentday western Oregon and Washington, which were an oceanic embayment.
2) 80-40 mybp: North America separates from Eurasia and rotates clockwise, centered on the
Colorado Plateau.
a) Subduction rate increases.
• Oceanic plate descends at a shallower angle and moves farther east before melting.
• Volcanic activity shifts from W to E across present Great Basin region.
3) 40-10 mybp: northern Mexico and southern California override the East Pacific Ridge.
a) Rotation of the continent centered on the Blue Mountains (northeastern Oregon).
b) Rate of subduction slows.
• Oceanic plate descends at steeper angle.
• Volcanic activity largely shifts from E to W across present Great Basin region.
c) Uplift and extension cause faulting that creates generally N-S ranges from Sierra
Nevada in California through Wasatch Mountains in Utah.
4) <10 mybp: Miocene-Pliocene Uplift elevates western USA and Rocky Mountains.
5) <2 mybp: Glaciers advance and retreat through Washington; mountain glaciers throughout
the region also expand and retreat.
CLIMATE, OCEAN CURRENTS, and TIDES
General Weather Patterns
Hadley Cells (see handout). In the tropics (about 0° latitude), air is heated and rises,
which causes it to cool and release precipitation (cool air holds less water than warm air). At
about 10 km in altitude, this rising air diverges to the north and south. It is pushed from below
by air moving into the area of low pressure created at the surface as the air rises.
In the subtropics (about 30° latitude), the cool air descends, and as it does, it becomes
warmer and drier (warmer air can hold more water, so the relative humidity drops). This
creates an area of high pressure (e.g., North Pacific High, discussed below) near the surface.
This air reaching the surface diverges away from the area of high pressure to the south (back
to tropics) and to the north. This circulation is complemented by a second area of rising air at
about 60° latitude, which creates a northern area of lower pressure (e.g., Aleutian Low,
discussed below).
Coriolis Effect and Major Pacific High and Low Pressure Areas (see handout).
The speed of the air rotating with the Earth is fastest near the equator and progressively
decreases at higher latitudes, because air at higher latitudes covers less distance than air near
the equator during the same period of time. The following explanation of the Coriolis effect
applies to the Northern Hemisphere.
As air shifts to the north, its relative speed as it circles the planet is greater than the
rotational speed of the Earth at the more northerly latitude, so the faster air moving north is
displaced to the right (to the east). As air shifts to the south, its relative speed as it circles the
planet is less than the rotational speed of the Earth at the more southerly latitude; thus, the
slower air moving south is also displaced to right (this time to the west). In the Northern
Hemisphere, air moving north or south is displaced to the right.
Therefore, air moving out from areas of high pressure is displaced to the right, which
creates a clockwise flow around the center of the high pressure area. Likewise, air moving
into areas of low pressure is also displaced to the right, which creates a counterclockwise flow
around the center of the low pressure area.
The North Pacific High (generally west of California) expands during the summer, as
the sun and warmer temperatures shift to the north, and it contracts during the winter, as the
sun shifts to the south. The clockwise rotation around the North Pacific High brings winds
generally from the northwest to the coast of the Pacific Northwest during the summer.
Conversely, the Aleutian Low to the north expands during the winter, as the sun shifts
to the south, and it contracts during the summer, as the sun shifts to the north. The
counterclockwise rotation around the Aleutian Low brings winds generally out of the
southwest along the coast of the Pacific Northwest during the winter.
Relative Temperatures and Precipitation: Along the Coast: Ocean temperatures are
relatively stable compared with temperatures on land, which fluctuate with changes in the
amount of solar radiation during the seasons. Thus, the temperature of the air moving onto
land is moderated by the ocean. During the winter, air moving onto land from the ocean is
relatively warmer than the air over the land, and during the summer, air moving onto the land
from the ocean is relatively cooler. Thus, the coast experiences warmer winters and cooler
summers than areas farther inland (in other words, the highest summer temperature and
lowest winter temperatures along the coast do not differ as much as they do at inland sites).
Relative Temperatures and Precipitation: In the Mountains: Temperatures at
higher elevations are relatively cooler than at lower elevations nearby. Air pressure decreases
as altitude increases; thus, heat is lost as air rises over the mountains, producing cooler
temperatures at higher elevations.
Rain Clouds Developing as Air Rises over Magdalena Mountains, Central New Mexico
Photograph by Mark Eberle, August 2008
As moisture-laden air moves to the east and rises over mountains, it cools, which
causes its capacity to hold water to decrease, so precipitation falls as the air moves up the
western slopes of mountains in the Northern Hemisphere. As the now drier air moves back
down the eastern slope of the mountain, it warms as it descends, which increases its capacity
to hold water (i.e., decreases its relative humidity), so conditions are more arid on eastern
slopes. Additionally (in the Northern Hemisphere), solar radiation is greater on south-facing
slopes, which increases evapotranspiration and creates drier conditions than on the northfacing slopes that receive less solar radiation. Thus, at the same elevations, conditions are
generally drier on the south-facing slope than on the north-facing slope, and conditions are
drier on the east-facing slope than on the west-facing slope.
Winter Rain and Summer Drought on the Pacific Northwest Coast. During the
winter, warm, subtropical moisture is pulled north into the low pressure area. It rises over
colder, polar air, which causes the air to cool and lose its ability to hold moisture, generating
rain. Additional moisture is lost as low pressure cells, moving generally to the east, rise over
the Olympic Mountains and the Coast Range, which similarly causes the air to cool, resulting
in precipitation. As much as 80% of the precipitation along the Pacific Northwest coast falls
from October through March, when the Aleutian Low expands southward. In addition, air
flowing into a low pressure cell accelerates (the circumference of rotation decreases), which
creates the strong, gusty winds associated with winter storms.
During the summer, warmer air holds more moisture, so only 5% of the annual
precipitation on the Pacific Northwest coast falls during July and August. However, fog is
produced along the coast during the summer. Air cools as it reaches the relatively cooler
ocean. The temperature of water changes much more slowly than the temperature of air,
which is why the ocean is relatively cooler than the air during the summer and relatively
warmer during the winter. The water temperature is even cooler along the coast where
summer upwelling occurs (described below). This cooling effect of the ocean on the air
increases the relative humidity of the air and, at about 45°F, the moisture condenses as fog.
This cool, moist air is relatively dense, so fog stays near the surface and spreads inland at
night as the temperature over the land cools. This fog layer slowly dissipates as the air and
land warm during the day, reducing the relative humidity. In addition, the speed of air flowing
out of a high pressure zone is more constant than wind associated with low pressure, and this
results in a generally lighter wind along the Pacific Northwest coast during the summer,
allowing the morning fog to persist.
Ocean Currents (see handout)
California Current and Summer Upwelling. The Subarctic Current (North Pacific
Drift) flows east across the northern Pacific Ocean and diverges north and south near the
Northwest coast. The California Current is the south-flowing branch that moves down the
coast of Washington, Oregon, and California. Because of the Coriolis effect, moving objects
veer to the right relative to the Earth in the Northern Hemisphere (as with high and low
pressure areas discussed above). Thus, during the summer, the prevailing winds and ocean
currents from the north where they flow parallel to the coast move the ocean water offshore
(to the right), which produces lower pressure and lower sea-levels near the coast (within about
15 km). Deeper water moves up to fill this "void"; this is referred to as upwelling.
Compared to surface water, the deeper water is cooler and contains more nutrients,
both of which are important to coastal ecosystems. The cooler water helps to generate summer
fog along the coast, which provides moisture to forest plants, in the form of "drip" from trees
(see additional comments for the redwood forests in the Highlights from Previous Trips
section of this website. The greater nutrient load in the upwelling supports an important
phytoplankton bloom that, in turn, supports other components of the coastal marine
ecosystem.
In general, winds that generate upwelling are not as strong or reliable off the coast in
the northwestern USA as they are in California, but the presence of deep, underwater canyons
off the Northwest coast enhances the nutrients in the rising water (NOAA website).
Variability in wind speed and direction and in physical features along the coastline affect the
extent of the upwelling. The greatest upwelling where we will travel occurs in 3 areas: 1) off
Tillamook in northern Oregon, 2) along the central Oregon coast between Florence and
Newport (or between the northern part of the Oregon Dunes and our campsite at Beverly
Beach), and 3) between Cape Blanco in southern Oregon and Cape Mendocino in northern
California (including the northernmost redwood forests).
Davidson Current. Winds from the south during the winter create the north-flowing
Davidson Current over the continental shelf. The California Current is pushed offshore (and
continues to flow south). The Davidson Current flowing from south to north helps to
moderate winter temperatures along the Pacific Northwest coast.
Waves. Waves are a vertical oscillation that gives the appearance of a horizontal
movement of the water. The height of waves increases as wind speed, duration, and distance
increase. The heights of swells along the Pacific Northwest coast are typically less than 2 m
during the summer. As waves approach the shallower depths along the shore, their energy is
dissipated. They become slower and steeper until they break, perhaps once or perhaps several
times before they reach the shore, depending on the vertical contour of the sea floor. The main
threat from waves to attached organisms along the shore is from the logs or other objects that
can be hurled against them by the waves. The higher the wave, the greater the energy that can
imparted to the log or other object.
Tides. The gravity of the moon exerts the greatest pull on water in the oceans closest
to it. The moon also pulls the Earth and pulls the oceans on the opposite side of the planet to
progressively lesser degrees. Thus, bulges of high water levels are created in the oceans
closest to and farthest away from moon = high tides. Depressions of low water levels are
created on Earth at 90° angles to the position of the moon = low tides. The gravity of the sun
also exerts gravitational pull on the water and the planet, but to a lesser degree than moon.
Generally, there are 2 high tides and 2 low tides per day as the Earth rotates under the
bulges and depressions, but the heights of the 2 low tides or the 2 high tides are not equal to
each other. The orbital plane of the moon is not the same as the rotational plane of the earth,
so the gravitational pull varies. As a result, the general sequence of the 2 high and 2 low tides
during a 24-hour period is: 1) higher high tide, 2) lower low tide, 3) lower high tide, and 4)
higher low tide. The lower low tides we will encounter will be early in the morning.
"Spring Tides" have nothing to do with seasons; they are the highest and lowest tides
that occur when the sun and moon form a roughly straight line with the Earth. During a new
moon, the sun and moon are pulling from same side. During a full moon, the sun and moon
are pulling from opposite sides. "Neap Tides" (moderate tidal changes) occur when the sun
and moon are at right angles to the Earth (during quarter moons).
The greatest differences in tides are during June and December, because these are
when the Earth is closer to the sun during its elliptical orbit. Tides also vary with surface
winds, atmospheric pressure, and other local phenomena (i.e., we want light winds and high
atmospheric pressure when we visit the tidepools). Thus, tide tables offer only predicted tide
levels. In the USA, tide heights are reported relative to the mean lower low tide (= 0 feet).
The best low tides for viewing tidepools are below average levels (e.g., -1.6 feet).
COMMUNITIES
Montane Communities (see Highlights from Previous Trips for additional information)
Temperature-Precipitation Gradients. As noted previously in this file, air
temperature decreases as elevation increases, and more solar radiation reaches southern
exposures of mountains in the northern hemisphere. Also, precipitation increases as elevation
increases, but more precipitation falls on the western slopes than on the eastern slopes of
mountains. Thus, temperature and precipitation form elevational gradients, which leads to
changes in the community. However, the transitions can be obscured by local features, such as
soil type. Dry conditions at low elevations limit tree growth in interior forests (excluding the
coastal rain forest), and cold conditions (short growing season) limit tree growth at high
elevations. Drier conditions on an eastern slope shift communities higher than on a western
slope. Similarly, as latitude decreases (i.e., as you move south), similar communities occur at
progressively higher elevations. For example, treeline at Mount Rainier, Washington (47°N
latitude) is ~1,800 m, but treeline at Mount Wheeler, Nevada (39°N latitude) is ~3,000 m.
Fire. Relatively frequent ground fires are important in the drier, interior forests,
especially at lower elevations, where pines often dominate. Fire limits undergrowth and
enhances reproduction of some species, such as lodgepole pine and sequoia (see additional
comments in the files for the Rocky Mountains and Sierra Nevada Forests). Pines and other
trees adapted to relatively frequent fires tend to lose their lower branches as they grow, which
helps to prevent the fires from spreading to their crowns. Sequoias and redwoods also have
thick, resin-free (less flammable) bark. Subalpine forests and coastal rain forests have lower
frequencies of fires (see table below). Subalpine trees often retain their lower branches, which
makes them susceptible to damage by fire. However, the pyramidal shape of subalpine trees is
more effective than the rounded tops of pines for shedding snow.
Table 1. Fire-return intervals over several centuries for forest communities in Oregon and
Washington from a literature summary by James K. Agee (1993. Fire ecology of Pacific
Northwest forests. Island Press, Washington, DC).
Oregon
ha
Forest type
woodland
ponderosa pine
mixed conifer
lodgepole pine
Douglas-fir
cedar/spruce/hemlock
subalpine
1,001,000
3,142,000
399,000
757,000
4,444,000
292,000
1,075,000
Fire cycle
(years)
25
15
30
80
150
400
800
Washington
Burned
ha
40,000
209,400
13,300
9,400
29,600
700
1,300
ha
12,000
1,438,000
504,000
211,000
3,068,000
1,291,000
935,000
Fire cycle
(years)
25
15
50
110
217
937
500
Burned
ha
500
95,800
10,100
1,900
14,100
1,400
1,900
Wind. Strong, gusty winds blow down trees during winter storms in temperate rain
forests. The opening created by the fallen tree permits more sunlight to reach below the
canopy to the forest floor. The downed tree also provides a growth platform ("nurse log") to
support saplings and other organisms as decomposition slowly recycles the nutrients
contained in the nurse log (see additional comments under "Olympic National Park/Coast
Range" under the Highlights from Previous Trips). The spiral growth of a tree (visible on
snags or fallen trees without bark) improves its flexibility and strength to resist wind damage.
Nutrients: a separate file includes text and images that explain relationships with
other organisms that help plants to obtain nutrients.
General Montane Communities. The following lists provide names for communities
from lowest to highest elevations. A distinctive riparian community crosses among these
elevational communities. For additional information about the various communities we visit,
see Highlights from Previous Trips and handouts.
• Interior Mountains (Sierra Nevada/Rocky Mountains/Great Basin/East-slope Cascade Mountains)
1. Grassland/Desertscrub
2. Foothills Woodland
3. Lower Montane Forest
4. Upper Montane Forest
5. Alpine Tundra
• Coastal Mountains (Olympic Mountains/Coast Range/West-slope Cascade Mountains)
1. Temperate Rain Forest
2. Lower Montane Forest
3. Upper Montane Forest
4. Alpine Tundra
Other Coastal Communities – Zonation. The following lists provide names for a
general sequence of communities in tidepools, estuaries, and coastal dunes. For additional
information about the various communities, see Highlights from Previous Trips and handouts.
• Tidepools (generally, desiccation sets the upper zones occupied by organisms, and
predation and competition set the lower zones)
1. Ocean
2. Low Intertidal Zone
3. Mid Intertidal Zone
4. High Intertidal Zone
5. Spray Zone
• Estuarine Watersheds (freshwater and high gradient at upper end; saltwater and low
gradient at lower end)
1. Upland Stream
2. Freshwater Wetland
3. Saltwater Wetland
4. Tidal Mudflats
5. Open Channel (Eelgrass)
• Coastal Dunes
1. Beach
2. Foredune
3. Beachgrass Hummocks and Deflation Plains
4. Transverse and Oblique Dunes
5. Transition Forest
Return to Course Homepage