ENV200 Chapter 5 Notes

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School of Environment
Romila Verma

CHAPTER 5 – BIOMES AND BIODIVERSITY [5.1] TERRESTRIAL BIOMES ­ Biomes = large biological communities; broad, regional types of ecosystems o Classified according to average annual temperature and precipitation (rainfall and snowfall) o Characterized by biodiversity ­ Biodiversity = the number and variety of different biological species that live in each biome o Create much of the structure and functions of an ecosystem o Generate emergent properties:  Productivity = the rate at which plants produce biomass  Varies from warm to cold climates, and from wet to dry environments  Homeostasis = stability  Depends on biodiversity and productivity  Resilience = the ability to recover from disturbance  Depends on biodiversity and productivity ­ There are 9 major biome types, which can be further divided into smaller classes o Many temperature controlled biomes occur in latitudinal bands  E.g., tropical forests occur near the equator  E.g., expansive grasslands occur near or beyond the tropics o Some biomes are named for their latitudes  E.g., tropical rainforests occur between Tropic of Cancer and Tropic of Capricorn  E.g., arctic tundra lies near or above the Arctic Circle ­ Temperature and precipitation change with elevation and latitude o Vertical zonation = vegetation zones defined by altitude ­ Understanding climate graphs o Moisture availability depends on temperature and precipitation o Evaporation depends on temperature o When evaporation (or temperature) exceeds precipitation, then dry climates o When precipitation exceeds evaporation (or temperature), then moist climates Tropical moist forests are warm and wet year-round ­ Cloud forests = occur high in the mountains where fog and mist keep vegetation wet all the time ­ Tropical rainforests = occur where rainfall is abundant and temperatures are warm to hot year-round ­ One of the most complex and biologically rich biome types in the world ­ Ample rainfall and uniform temperatures ­ Soil tends to be thin, acidic, and nutrient-poor ­ Distinctive nutrient cycles o About 90% of all the nutrients are contained in the bodies of the living organisms o Rapid decomposition, recycling, and incorporation of dead organic material immediately back into living biomass Tropical seasonal forests have annual dry seasons ­ Distinct wet and dry seasons ­ Year-round hot temperatures ­ Often open woodlands that grade into savannas ­ Tropical seasonal forests = drought-tolerant forests that look brown and dormant in the dry season but burst into vivid green during rainy months o Dry much of the year, but periodic rain to support plant growth o Many of the trees and shrubs in a seasonal forest are drought-deciduous o Drought-deciduous = lose leaves and cease growing when no water is available ­ More attractive than tropical moist forests for human habitation o More degradation due to settlement o Fewer insects, parasites, and fungal diseases o Healthier place for humans to live ­ Soil has higher nutrient levels and is more agriculturally productive (compared to tropical moist forests) ­ Highly endangered Tropical savannas and grasslands are dry most of the year ­ Savannas = open grasslands or grasslands with sparse tree cover ­ Annual drought and rainy seasons ­ Year-round warm temperatures ­ Rainy season is less abundant than in a forest (e.g., too little rainfall to support forests) ­ During dry seasons, fires can sweep across a grassland o Killing off young trees o Keeping the landscape open ­ Many adaptations to survive drought, heat, and fires o Deep, long-lived roots  Seek groundwater  Persist when leaves and stems above the ground die ­ After a fire or drought, fresh green shoots grow quickly from the roots o Susceptible to grazing pressure from domestic livestock Deserts are hot or cold, but always dry ­ Precipitation is sporadic and low ­ Vegetation is sparse, but can be diverse ­ Most plants and animals are adapted to survive long droughts, extreme heat, and often extreme cold o Water-storing leaves and stems o Thick epidermal layers to reduce water loss o Salt tolerance ­ Many plants are drought-deciduous ­ Most desert plants bloom and set seed quickly after rainfall ­ Warm, dry, high-pressure climate conditions o Desert regions = occur at about 30° north and south o Extensive deserts = occur in continental interiors (rain is rare; evaporation rates are high) ­ Many animals are specially adapted o Nocturnal o Get moisture from seeds and plants o Highly concentrated urine and nearly dry feces to eliminate body waste without losing moisture ­ Sparse, slow-growing vegetation is quickly damaged by off-road vehicles ­ Soils recover slowly ­ Vulnerable to overgrazing o Livestock are destroying much of the plant cover o Bare, dry soil becomes drifting sand  Without plant roots and organic matter  Soil loses its ability to retain what rain does fall  Land becomes progressively drier and more bare o Restabilization is extremely difficult Temperate grasslands have rich soils ­ Occur at mid-latitudes on all continents ­ Enough rain to support abundant grass but not enough for forests ­ Extreme temperatures, dry conditions, and periodic fires ­ High plant and animal diversity ­ Complex, diverse mix of grasses and forbs (flowering herbaceous plants) ­ Deep roots help to survive drought, fire, and extreme heat and cold ­ Deep roots, together with an annual winter accumulation of dead leaves on the surface, produce thick, organic-rich soils ­ Many have been converted to farmland ­ Vulnerable to overgrazing o Excessive grazing eventually kills even deep-rooted plants o As ground cover dies off, soil erosion results, and unpalatable weeds spread Temperate scrublands have summer drought ­ Dry environments ­ Shrubs, trees, and grass are drought-adapted ­ Very biologically rich ­ Mediterranean climate = hot season coincides with the dry season to produce hot, dry summers and cool, moist winters ­ Evergreen shrubs = small, leathery, sclerophyllous (hard, waxy) leaves that form dense thickets ­ Scrub oaks, drought-resistant pines, or other small trees cluster in sheltered valleys ­ Periodic fires ­ Chaparral = annual spring flowers often bloom profusely, especially after fires ­ Many animals are drought-tolerant ­ Does not cover a very large total area ­ Contains a high number of unique species ­ Considered a “hot-spot” for biodiversity ­ Highly desired for human habitation Temperate forests can be evergreen or deciduous ­ Wide range of precipitation conditions ­ Occur mainly between about 30° and 55° latitude ­ Nutrients are held within the soil and made available for new plant growth ­ Deciduous forests = broad-leaved trees that lose their leaves in the winter (e.g., maples, birch, aspen, alder) o Year-round precipitation o Winters near or below freezing o Rainfall is plentiful o Loss of green chlorophyll pigments in autumn o Dense canopy in summer o Diverse understory in spring  Spring ephemeral (short-lived) plants produce lovely flowers  Vernal (springtime) pools support amphibians and insects  Shelter a great diversity of songbirds o Most of the eastern deciduous forests were cut for firewood, lumber, and industrial uses, and cleared for farmland when European settlers first came to North America  Many of these regions have now returned to deciduous forest, but the dominant species may have changed o Moist, moderate climates o Able to regrow quickly o Human impacts are extensive (e.g., deforestation)  Most native species are somewhat threatened ­ Coniferous forests = evergreen, cone-bearing trees (e.g., pines, hemlocks, spruce, cedar, fir) o Occur in a wide range of environmental conditions o Occur where moisture is limited  In cold climates, moisture is unavailable (frozen) in winter  In hot climates, there are seasonal droughts  Sandy soils hold little moisture and often occupied by conifers o Thin, waxy leaves (needles) help these trees reduce moisture loss o Provide most wood products in North America and other regions o Temperate rainforests = coastal forests that grow in extremely wet conditions  Cool, rainy forest often enshrouded in fog o Leaf drip = condensation in the canopy  Major form of precipitation in the understory o Year-round mild temperatures o Abundant but often seasonal precipitation o Often experience dry summers o Able to survive winter cold o Dominate the boreal forests, or the northern forests o Slow-growing  Cold temperatures  Short frost-free growing season  Moderate precipitation o Trees are cold-tolerant and drought-tolerant o Favorite places for hunting, fishing, recreation, and extractive resource use o Taiga = the extreme, ragged edge of the boreal forest, where forest gradually gives way to open tundra  Extreme cold and short summer limits the growth rate of trees Tundra can freeze in any month ­ Year-round below freezing temperatures ­ Only small, hardy vegetation can survive ­ Tundra = treeless landscape o Occurs at high latitudes or on mountaintops o Growing season of only two to three months o May have frost any month of the year ­ Considered a variant of grasslands because it has no trees ­ Considered a very cold desert because water is unavailable (frozen) most of the year ­ Plant diversity is relatively low ­ Frost can occur in summer ­ Too cold for most human activities ­ Not as badly threatened as other biomes ­ Problems o Global climate change may be altering the balance of some tundra ecosystems o Air pollution from distant cities tends to accumulate at high latitudes o Overabundant populations of snow geese threatens costal tundra in eastern Canada o Oil and gas drilling threatens tundra in Alaska and Siberia ­ Arctic tundra = short growing season and low productivity o During midsummer, 24-hour sunshine supports a burst of plant growth and insect life o Birds migrate to the Arctic every year  Feast on the abundant invertebrate and plant life  Raise their young  Carry energy and protein from high latitudes to low latitudes o Essential for global biodiversity, especially for birds ­ Alpine tundra = occur on or near mountaintops o Environmental conditions and vegetation similar to arctic tundra o Short, intense growing season o Everything must flower at once in order to produce seeds in a few weeks before snow arrives o Many plants have deep pigmentation and leathery leaves to protect against UV light [5.2] MARINE ENVIRONMENTS ­ Biological communities in oceans and seas are poorly understood, but are probably as diverse and complex as terrestrial biomes ­ Most marine communities depend on photosynthetic organisms, like land-based systems o Algae or phytoplankton support the marine food web, rather than trees and grasses  Phytoplankton = tiny, free-floating photosynthetic plants o Photosynthetic activity tends to be greatest near coastlines, where nitrogen, phosphorus, and other nutrients wash offshore and fertilize primary producers o Ocean currents contribute to the distribution of biological productivity Open ocean communities vary from surface to hadal zone ­ Ocean systems can be described by depth and proximity to shore o Littoral zones = shoreline environment  Intertidal zone = area exposed to low tides o Pelagic zones = water column; surface of ocean  Epipelagic zone  Has photosynthetic organisms  Mesopelagic zone  Bathypelagic zone o Benthic zones = bottom of the ocean  Abyssal zone  Hadal zone o Continental shelf =
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