Ecology Physical Environment and Climate

Ecology Physical Environment and Climate - The Physical...

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Unformatted text preview: The Physical Environment: The Physical Environment: Climate Climate is a long term environmental condition or weather pattern. This distinguishes climate from weather. Weather is the environmental condition prevailing today and in the short term. The Physical Environment: The Physical Environment: Climate A climatic pattern is determined by the distribution of heat (measured by temperature) and moisture on a yearly basis at a particular location on the globe. The Physical Environment: The Physical Environment: Climate Both temperature and moisture patterns are associated with latitude; but are altered by: 1. prevailing winds, 2. mountain ranges, and 3. presence or absence of local bodies of water (oceans and lakes). The Physical Environment: The Physical Environment: Climate In other words, climate is the result of combination of: 1. Differential heat originating as electromagnetic radiation from the sun (a function of latitude); 2. Moisture availability (partially a function of latitude); The Physical Environment: The Physical Environment: Climate 3. Prevailing winds (modified by the Coriolis force); and 4. Local features of landscape (bodies of water, mountains etc.). Latitude: Latitude: Tropical Wet Forests Latitude: Latitude: Location of Deserts The Physical Environment: The Physical Environment: Climate Temperature Every point on the globe receives the same number of hours of electromagnetic radiation (ER) per year. energy. But not the same amount of The Physical Environment: The Physical Environment: Climate The amount of energy received as well as the distribution over time (seasonal variation) depends on latitude. The Physical Environment: The Physical Environment: Climate This is because: the maximum rate of conversion of Light Energy (Electromagnetic Radiation) into heat occurs when the sun is directly overhead. The Physical Environment: The Physical Environment: Climate The rate of conversion of Light Energy (Electromagnetic Radiation) into heat energy declines as a function of latitude outside of the tropics since the sun is at lower and lower angles and light energy is spread over larger surface areas. The Physical Environment: The Physical Environment: Climate In addition, variation in day length is: minimized in tropical latitudes and maximized in polar latitudes. The sun is directly overhead only in tropical latitudes. The Physical Environment: The Physical Environment: Climate Definition of the tropics: those latitudes where the sun is directly overhead at noon at least once a year. Occurs within 23.5o N (Tropic of Cancer) and 23.5o S (Tropic of Capricorn). The Physical Environment: The Physical Environment: Climate Day Length is approximately 12 hours per day all year long at the equator. The Physical Environment: The Physical Environment: Climate But, at the highest latitudes (near the North and South Poles) the sun may never set at the height of summer (June 21 in Northern Hemisphere) and may never move above the horizon in the height of winter. The Physical Environment: The Physical Environment: Climate In the tropics, the sun is directly overhead at the equator at the time of the equinoxes (March 21, Sept. 21), at which time all areas of the Earth have 12 hours of daylight. The Physical Environment: The Physical Environment: Climate On June 21, the longest day of the year in the Northern Hemisphere, the sun is directly overhead at the Tropic of Cancer. The Physical Environment: The Physical Environment: Climate On December 21, the sun is directly overhead at the Tropic of Capricorn. This date is also the shortest day on the year in the Northern Hemisphere and the longest day of the year in the Southern Hemisphere. The Physical Environment: The Physical Environment: Climate In the tropics then, except at the very limits, the sun will be directly overhead twice a year. The Physical Environment: The Physical Environment: Climate Seasonality is based mainly on: temperature in the “temperate” and polar zones; and rainfall in the tropics. That is, wet versus dry seasons in the tropics. The Physical Environment: The Physical Environment: Climate In the tropical latitudes, daily variation in temperature (day versus night) can be much greater than seasonal variations in daily highs and lows. Properties of Air Properties of Air 1. 2. Warm air has a much greater capacity to hold moisture as compared to cool air. Warm air is less dense than cool air and therefore rises. Properties of Air Properties of Air Locally (as opposed to global air circulation), at night cool air sinks and settles in low areas. This air will heat up again during the day. Global Air Circulation Global Air Circulation On a regional and global scale, during the day, warm air rises and cools as it leaves the surface of the Earth and enters the atmosphere. Properties of Air Properties of Air During the day, sunlight is absorbed by land masses, and energy is converted into heat. Air near the ground is heated, it becomes less dense and rises, producing large areas of rising air masses. Properties of Air Properties of Air As warm air masses gain altitude they eventually cool, moisture condenses, clouds form, and the result is precipitation. Properties of Air Properties of Air As rising air masses cool high in the atmosphere, the associated high altitude land formations experience cold air temperatures. The general rule is that air temperature drops 5.5o C per 1000m of elevation. Table 1. Mean temperature by altitude at various locations in Costa Rica, 1968 Location Limon Golfito Nicoya Tilran El Coco San Jose El Guarco Altitude Degree Temperature Mean Rainfall (m) s (mm) Latitude 3 15 130 562 920 1172 1433 10 8 10 10 10 10 9.5 24.9 28.5 26.3 23.6 22.5 20.4 18.7 3574 4575 2438 2503 2244 2300 1880 The Physical Environment: The Physical Environment: Climate Rainfall amounts vary by latitude, but are also determined by: 1. 2. 3. proximity to the ocean or other large bodies of water; the prevailing winds; mountain ranges. The Physical Environment: The Physical Environment: Climate In most cases, tropical locations receive more rainfall than temperate or boreal locations. Table 2. Annual precipitation amounts from selected temperate and tropical regions Location Cañas, Costa Rica Midwestern US East Coast of the US Amazon Basin Foothills of the Andes Biome Type Tropical Deciduous Forest Annual Precipitation 1763 Prairie (Temperate 500­1000 Grassland) Temperate Deciduous 1000­1500 Forest Tropical Wet Forest 1500­3000 Tropical Wet Forest 5000 Global Rainfall Patterns Global Air Circulation Patterns Global Air Circulation Patterns 1. Determined by convection cells and 2. the Coriolis force. Global Air Circulation Patterns Global Air Circulation Patterns 3. Convection Cells plus Coriolis Force combine to produce the prevailing winds. 4. The prevailing winds, in turn, determine the ocean currents, which affect local terrestrial climates. Convection Cells Convection Cells Thermal Equator 60o N 30o N 23o N 0o 23o S 30o S Tropic of Cancer Sun directly overhead. Equator Tropic of Capricorn September 21 March 21 60o S Thermal Equator 60 o N 30 o N 23 o N 0 o Tropic Equat or 23 o S 30 o S 60 o S of Can cer Sun directly overhead. Tropic of Cap ricorn June 21 Thermal Equator o 60 N cer of Can Tropic or Equat o 30 N o 23 N rn aprico of C ropic T 0o 23 S o o 30 S o 60 S Sun directly overhead. December 21 60o N Warm air moves up and away from the equator towards the poles. 30o N 23o N 0o 23o S 30o S 60o S Cold air also moves along the surface of the Global Air Circulation Patterns Global Air Circulation Patterns The Coriolis Force is based on the fact that the Earth is rotating on its axis; Areas closer to the axis of rotation (high latitudes) are moving through the air masses more slowly than areas nearer the equator. Global Air Circulation Patterns Global Air Circulation Patterns At 45o N latitude the Earth moves through the atmosphere at 17,000 miles/day. At the equator, the equivalent speed is 24,000 miles/day. Coriolis Effect Direction of Spin N Space path N Path on Earth S S The Physical Environment: The Physical Environment: Climate The result: 1. Air masses in the Northern Hemisphere are deflected to the right as they move along the surface of the earth. 2. Air masses in the Southern Hemisphere are deflected to the left. Prevailing Winds Prevailing Winds Global Air Circulation Patterns Global Air Circulation Patterns Prevailing winds in the Northern Hemisphere: From the Northeast in the Tropics; 2. From the West in the Temperate Zone (north of the tropics); 3. From the East in the Polar Regions. 1. Global Air Circulation Patterns Global Air Circulation Patterns Prevailing Winds in the Southern Hemisphere: From the Southeast in the Tropics; 2. From the West in the Temperate Zone (north of the tropics); 3. From the East in the Polar Regions. 1. The Physical Environment: The Physical Environment: Climate Deserts are found in two situations: 1. At or near 30o latitude. 2. On the leeward side (as opposed to windward side) of the prevailing winds. The Physical Environment: The Physical Environment: Climate These latter are often called mountain shadow deserts. Examples: 1. west side of mountains in the tropics; 2. east side of mountains in the temperate zone Ocean Currents Ocean Currents Ocean currents are the movement of surface waters in the oceans. They are the result of being pushed by the prevailing winds. Ocean Currents Ocean Currents Ocean currents follow the prevailing winds, but are also shaped by the positions of the continents. Ocean Currents Ocean Currents Ocean Currents The Gulf Stream, for example, is produced by the presence of the Central American land bridge, and influences climates as far away as the British Isles. Ocean Currents Ocean Currents The Physical Environment: The Physical Environment: Climate Oceanic climates (or climates near large bodies of water) tend to be moister and have less extremes of temperate. Continental climates are drier and have greater extremes of temperature. Microclimates 1. Light. In a mature forest less than 1% of incident light may reach the forest floor. Mason Neck State Park Microclimates 2. Relative humidity is often 80­100% near the ground but only 60% in the canopy. 3. Temperature variations near the ground: 1.4 ­ 3.2oC but 7.2 ­ 12.4o C at 18 meters from the ground. Microclimates Microclimates 4. Wind speed is much greater at higher portions of forest canopy, much less near ground. Microclimates Microclimates 1. Microclimates on hills vary depending on location and aspect. Microclimates Microclimates 1. 2. Location: Top of hill, warmer, drier, sunnier. Bottom of hill, cooler, moister, fewer hours of direct sunlight. Microclimates Aspect is north­facing versus south­ facing slopes. In the Northern Hemisphere: south­facing slopes almost always face the sun and are warmer and drier. north­facing slopes are almost always in the shade and are moister and cooler. February 5, 2005, North Side February 5, 2005, North Side February 5, 2005, South Side February 5, 2005, South Side February 5, 2005, South Side February 5, 2005, South Side February 5, 2005, North Side February 5, 2005, North Side Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Biomes are regional ecosystem types. Terrestrial biomes reflect the prevailing climate, specifically temperature and moisture availability. The log of above ground plant productivity can be predicted by the log of total evapotranspiration. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Evapotranspiration equals the total amount of water returned to the atmosphere by the combined processes of evaporation and plant transpiration. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Evapotranspiration is a surrogate for the combined effects of: light, 2. temperature, and 3. moisture availability. 1. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Holdridge and others found that one can also predict what type of vegetation will be present in an ecosystem as long as temperature and moisture data are available. Biomes Biomes Biomes, or regional ecosystem types, can be graphed and maps of biome distributions developed as follows. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Holdridge developed a more detailed system and applied it to both temperate and tropical ecosystems. His system has many levels, but the basic level is determined by two parameters: 1. 2. Mean annual biotemperature Total annual precipitation Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Mean annual biotemperature is just what it sounds like except all daily temperatures below zero or above 30oC are scored as zero. Holdridge was interested in temperatures producing net positive productivity. At temperatures below zero or above 30, net productivity is zero. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Total annual precipitation was used rather than length of the dry season since it was simpler and just as effective, according to Holdridge. As we can see in a later slide, Holdridge used a base 2 model. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System A typical life zone is name for: the latitudinal region, 2. the altitudinal belt, 3. the humidity province, 4. the prevailing vegetation (forest, scrub, etc.). 1. Biomes and the Holdridge Life Biomes and the Holdridge Life Zone System Typical names: 1. 2. 3. 4. Tropical wet forest Tropical montane wet forest Temperate moist forest Boreal dry scrub Questions? ...
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This note was uploaded on 01/23/2012 for the course BIOL/EVPP 307 taught by Professor Crerar during the Summer '11 term at George Mason.

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