Lecture 7 Background

Ricklefs Ch 4 pg76-84

Surface Winds & Rain Shadows

-Global wind patterns interact with other features of the landscape to create precipitation
-As dry air descends the leeward slope and travels across lowlands beyond it, air picks up moisture and creates arid environments called rain shadows
-Great Basin deserts of western US and Gobi Desert of Asia are in rain shadows of extensive mountain ranges

Topographic Influences on Climate

-Topography and geology modify the environment on a local scale within regions of otherwise uniform climate
-Adiabatic cooling: decrease in temperature with increasing elevation caused by the expansion of air under decreasing atmospheric elevation
-Changes in plant communities with elevation result in more or less distinct belts of vegetation; these are referred to as life zones

Climate & Underlying Bedrock Interact to Diversify Soils

-Climate affects the distribution of plants and animals indirectly through its influence on the development of soil
-Characteristics of soil determine its ability to hold water and to make available he minerals required for plant growth
-Soil: layer of chemically and biologically altered material that overlies rock or other unaltered material at the surface of the Earth
-Horizons: distinct layers in soil; soil profile has several divisions that are referred to as the O, A, E, B, C, R horizons (from the surface downward)
-5 factors determine the characteristics of soils: climate, parent material, vegetation, local topography, age
-Soil horizons reveal the decreasing influence of climatic and biotic factors with increasing depth
-Soils exist in a dynamic state, changing as they develop on newly exposed rock


-The physical and chemical alteration of rock material near the earth's surface; occurs wherever surface water penetrates
-Initial chemical alteration of rock occurs when water dissolves some of its more soluble minerals, esp. sodium chloride and calcium sulfate
-Key aspect of weathering is the displacement of certain elements in the minerals feldspar, mica, and quartz; (notably calcium, magnesium, sodium, and potassium by hydrogen ions), followed by the reorganization of the remaining oxides into new minerals
-Where do these hydrogen ions come from? 1:Carbonic acid that forms when CO2 dissolves in rainwater; 2:the oxidation of organic material in the soil itself
-Cation exchange capacity: ability of a soil to retain positively charged ions, which provides an index to the fertility of that soil
-Soil fertility improves with time, up to a point
-Weathering is most severe under tropical conditions of high temp and rainfall


-The breakdown and loss of clay particles in the acidic soils of cold, moist regions
-This process reduces fertility of the upper layers of soil
-Acidic soils occur primarily in cool regions where needle-leaved trees dominate the forests


-The leaching of silicon from soil due to weathering under warm, moist conditions, leaving oxides of iron and aluminum to predominate
-This causes the soil to have a reddish coloration
-One of the consequences of laterization is that many tropical soils have low cation exchange capacity

Chapter 5
Biomes: biological and ecosystem communities categorized by climates and dominant plant forms—only plants of certain growth forms (physical structures) are able to survive in certain biomes/climates based on factors like water and nutrient demands

Distributions of plants can reflect differences in tolerable condition ranges in biomes

Climate Zone: Based on cycles of temperature and precipitation, charted in systems, first developed by Heinrich Walter, and further graphed by Charles Whittaker.

Temperate Zones

Usually have average annual temperatures from 5-20 degrees Celsius. Seasonal forests in those zones (i.e. eastern U.S., most of mainland Europe, and a good part of the Far East) have the nemoral climate (moderate with freezing winters) and frost-resistant, deciduous forest plants. Soils there are usually podsolized, slightly acidic, moderately leached, and have a lot of organic matter, but some may be drier, with a lot of sand and fewer nutrients—evergreen trees tend to grow there. Rain forests in these zones (i.e. Pacific Northwest, the very southernmost tip of South America, Eastern Australia, and New Zealand) have mild winters with heavy rains and foggy summers, and especially tall, ancient evergreens grow there. Grasslands (prairies in central U.S and steppes in central Asia), have rich, slow-decomposing soils, and infrequent precipitation, and plants well adapted to dry conditions and fires, and deserts have generally cool winters and hot summers, and tend to grow plenty of shrubs. Woodlands and shrublands (Mediterranean, and also a little bit on the U.S. west coast and southeast South America) have mild, rainy winters and especially dry summers and have evolved thick, evergreen shrubs with hard leaves (sclerophyllous). Subtropical deserts (parts of SW North America and NW and eastern Central America, Mid-southwestern and southeastern South America, north Africa and much of the Middle East, a bit of southern Africa, and most of Australia) have high atmospheric pressure owing to the descending Hadley cells, and have little rainfall, high temperatures, long growing seasons and arid soils with little organic matter. Plenty of succulents, shrubs, and small trees grow there, and most of those deserts have intermittent summer rains from which herbaceous plants briefly grow and bloom.

Boreal and Polar Zones

Average temperatures less than 5 degrees Celsius, generally low productivity and decomposition, vegetation usually evergreen. Boreal forests (taigas, in much of northern North America, i.e. much of Alaska and Canada, and a long strip of northern Eurasia) have severe winters, with a good bit of precipitation and moist soils throughout the growing season (only as much as 100 days!) due to low evaporation. Generally grow needle-leaved evergreen trees, with acidic, podolized soils and low fertility. Tundras (mainly northernmost Arctic zones, though maybe a few at high elevations in the Alps) have no trees, permanently frozen soil (permafrost) which thaws from 0.5-1 m in the brief growing season, with low precipitation (and 24 daylight hours in a day!), although saturated soils in the lower areas (warmer and longer growing seasons, less severe winters, greater productivity, more well-drained soils, and higher diversity in the Alps).

Tropical Zones

Average Temperatures usually over 20 degrees Celsius, with constant growth of plants. Rainforests (middle, equatorial and some of western South America, parts of Central America along the Gulf of Mexico and in the Caribbean islands, middle Africa, Madagascar, and bits of southeast Asia and practically all of the Malay/Indonesia archipelago and a bit of Northern Australia) have lateritic soils, fairly continuous rainfall, with a high tree canopy with a few emergent ones above it, and understory layers with woody vines (lianas) and epiphytes (i.e. bromeliads), with some of the highest species diversities and productivities known! Seasonal forests and savannas (most of Central America, areas of South America around the rainforest, most of the lower half of Africa, most of south and southeast Asia, and northern Australia) have deciduous trees which shed at times when there is little water (which occurs at either end of the year, with a heavy rainy season in the middle), thorny forests, and deserts, and wide grasslands (savannas).

Freshwater systems

Have characteristics in the water which do not necessarily reflect the climate, and thus may not be defined as "biomes" per se. Aquatic ecosystems all interact with the surrounding terrestrial ecosystems.
Flowing (lotic) waters, i.e. streams and rivers, can join and grow at distances along them. Rivers generally have a continuum of different life forms existing at the headwaters, midwaters, and downstream waters (the last are generally warmer, slower, and more nutrient-rich than the others). Rivers may have rapidly running, rocky riffles and deeper, slower pools, which are less productive than other areas. Streams also have areas of seasonally flooded and saturated vegetation growth called riparian zones. Nutrients may be allocthonous, coming from exterior sources such as leaf litter, or autocthonous, growing in the water (i.e. water plants or algae). Lotic systems are very sensitive to alterations to their flow, in particular man-made ones such as dams.

Standing (lentic) waters, i.e. ponds and lakes, generally don't flow, and form in depressions. They are usually divided into ecological zones with distinct physical conditions, including the shallow littoral zone, where rooted plants grow, the limnetic/pelagic zone, open water where phytoplankton is found. This can in turn be divided into the epilimnion (area towards the surface where light can shine through—a major issue in the Great Lakes is that the photic zone is increasing thanks to the zebra mussels, and thus allow more of a certain algae to grow on the bottom) and the hypolimnion (deeper areas). Then, the benthic zone includes the sediment on the bottom of the lake, where burrowing animals and microorganisms can live.

Wetlands: areas of land with saturated soil which supports vegetation that tolerates low soil oxygen, on the borders of aquatic and terrestrial communities—include freshwater swamps, marshes, and bogs, and marine salt marshes and mangrove wetlands.

Estuaries: areas at the mouths of rivers enclosed by land areas—freshwater and saltwater mixes, and nutrients and sediments deposit there, and thus support lots of production.

Eutrophication: adding limiting nutrients (i.e. phosphorus) to aquatic ecosystems—a perfectly natural process which is often hastened by human activity.

Marine systems

Divided by depth
Littoral (intertidal) zone: between high and low tide levels, exposed to air at times, occupied by creatures that can tolerate air.
Neritic zone: up to 200 meters deep after the low tide, to edge of continental shelf; highly productive
Oceanic zone: abrupt dropoff to depths, with sparse nutrients and limited production; there is also a benthic zone at the bottom.

Neritic and oceanic zones have photic (enough light for photosynthesis) and aphotic (light-free) zones (there are some in lakes too as mentioned before).

Most productive areas of the world ocean biomes: Polar oceans, temperate shelves and seas, temperate and tropical upwellings, and coral reefs.

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