03. BIOMES

• Biome


  General type of communities with similar climate conditions, growth patterns, and vegetation types
• Terrestrial biomes


  • Characteristics of biological communities vary with temperature, precipitation, and latitude
  • Hot, humid regions generally have greater biological productivity than cold or dry regions
  • Climate graphs are used to describe and compare precipitation and temperature in different biomes
  • Temperature and precipitation are the most important determinants in biome distribution on land
  • If the general temperature range and precipitation level is known, the kind of biological community likely to occur there can be predicted in the absence of human disturbance
  • Vertical zonation occurs as vegetation type change rapidly from warm and dry to cold and wet as you go up a mountain
• Tropical moist forests


  • Cloud forests - found high in the mountains where fog and mist keep vegetation wet all the time
  • Tropical rainforests - occur where rainfall is abundant (more than 200 cm per year) and temperatures are warm to hot year-round
• The soil of tropical moist forest types tends to be old, thin, acidic, and nutrient-poor, yet an enormous number of species can be present
• Tropical seasonal forests


  • Drought-tolerant forests that look brown and dormant in the dry season but burst into vivid green during rainy months
  • Often called Dry Tropical Forests because they are dry much of the year; however, there must be some periodic rain to support tree growth
  • Many of the trees and shrubs in a seasonal forest are drought-deciduous: they lose their leaves and cease growing when no water is available
  • Seasonal forests are often open woodlands that grade into savannas
• Tropical savannas and grasslands


  • Grasslands - also known as prairies or steppes; receive between 25 and 75 cm of rain per year
  • Savannas - extensive grasslands w/ occasional or patches of trees; typically tropical w/ 50-150 cm of rain per year
  • Like tropical seasonal forests, most tropical savannas and grasslands have a rainy season, but generally the rains are less abundant or less dependable than in a forest
  • During dry seasons, fires can sweep across grassland, killing off young trees and keeping the landscape open
  • Savannas and grassland plants have many adaptations to survive drought, heat, and fires
  • Grazing pressure from domestic livestock is an important threat to both the plants and the animals of tropical grasslands and savannas
• Desert


  • Occur where precipitation is rare and unpredictable, usually with less than 30 cm of rain per year
  • Their vegetation is sparse, but it can be surprisingly diverse, and most desert plants and animals are highly adapted to survive long droughts and extreme heat, and many can survive extreme cold
  • Desert is more vulnerable, sparse, slow-growing vegetation is quickly damaged by off-road vehicles
  • Desert soils recover slowly
  • Desert is also vulnerable to overgrazing
• Temperate grasslands


  • As in tropical latitudes, temperate (mid-latitude) grasslands occur where there is enough rain to support abundant grass but not enough for forests
  • Most grassland is a complex, diverse mix of grasses and flowering herbaceous plants, generally known as forbs
  • Deep roots help plants in temperate grasslands and savannas survive drought, fire, and extreme heat and cold. These roots, together with an annual winter accumulation of dead leaves on the surface, produce thick, organic-rich soils in temperate grasslands
• Temperate shrublands


  • Evergreen shrubs with small, leathery, sclerophyllous (hard, waxy) leaves form dense thickets
  • Scrub oaks, drought-resistant pines, or other small trees often cluster in sheltered valleys. Periodic fires burn fiercely in this fuel-rich plant assemblage and are a major factor in plant succession
  • In California, this landscape is called chaparral, Spanish for "thicket"
  • These areas are inhabited by drought-tolerant animals such as jackrabbits, kangaroo rats, mule deer, chipmunks, lizards, and many bird species
  • Very similar landscapes are found along the Mediterranean coast as well as southwestern Australia, central Chile, and South Africa
• Deciduous forests


  • Broadleaf forests occur throughout the world where rainfall is plentiful
  • In mid latitudes, these forests are deciduous and lose their leaves in winter
  • At lower latitudes, broadleaf forests may be evergreen or drought-deciduous
  • Can re-grow quickly because they occupy moist, moderate climates
• Coniferous forests


  • Grow in a wide range of temperature and moisture conditions
  • Often they occur where moisture is limited: in cold climates, moisture is unavailable (frozen) in winter; hot climates may have seasonal drought; sandy soils hold little moisture, and they are often occupied by conifers
  • Provide most wood products in North America
  • Coniferous forests of the Pacific coast grow in extremely wet conditions. The wettest coastal forests are known as temperate rainforest, a cool, rainy forest often enshrouded in fog

  
• Boreal forest

  • Mountainous areas at lower latitudes may also have many characteristics and species of the boreal forest
  • Dominant trees are pines, hemlocks, spruce, cedar, and fir
• Boreal Forest


  Also known as Northern Forests, lie between about 50 and 60 degrees north
• Boreal Forest


  • Some deciduous trees are also present, such as maples, birch, aspen, and alder
  • Slow-growing because of the cold temperatures and a short frost-free growing season, but they are still expansive resources
• Taiga


  The extreme, ragged edge of the boreal forest, where forest gradually gives way to open tundra
• Tundra


  A treeless landscape that occurs at high latitudes or on mountaintops, has a growing season of only two or three months, and it may have frost any month of the year
• Tundra


  • A variant of grasslands because it has no trees
  • Very cold desert because water is unavailable (frozen) most of the year
• Arctic Tundra


  An expansive biome that has low productivity because it has a short growing season. During midsummer, 24-hour sunshine supports a burst of plant growth and an explosion of insect life
• Alpine Tundra


  Occurring on a near mountain top, has environmental conditions and vegetation similar to arctic tundra. These areas have a short, intense growing season. Many alpine tundra plants also have deep pigmentation and leathery leaves to protect against the strong ultraviolet light in the thin mountain atmosphere
• Marine Ecosystem


  • Vary mainly with depth, temperature, and salinity
  • Coral reefs and estuaries are among the world's most productive and diverse ecosystem
  • Vertical stratification is a key feature, mainly because light decreases rapidly with depth, and communities below the photic zone must rely on energy sources other than photosynthesis to persist
  • Temperature also decreases with depth and affects the amount of oxygen and other elements that can be absorbed in water
• Phytoplankton


  Microscopic floating algae that carry on photosynthesis in pelagic ecosystem
• Zooplankton


  Small, weakly swimming animals that feed on phytoplankton
• Ocean Systems based on depth and proximity to shore

  • Benthic – communities occur on the bottom
  • Pelagic zone – (from "sea" in Greek) are the water column
  • Epipelagic zone – (epi = on top) has photosynthetic organisms. Below this are the mesopelagic (meso = medium), and bathypelagic (bathos = deep) zones
  • Deepest layers: Abyssal Zone (to 4,000 m) and Hadal Zone (deeper than 6,000 m)
  • Littoral Zones – shorelines
  • Intertidal Zone – area exposed by low tides
• Coral Reefs


  Among the best-known marine ecosystems because of their extraordinary biological productivity and their diverse and beautiful organisms
• Mangroves


  Trees that grow in salt water. They occur along calm, shallow, tropical coastlines around the world. Mangrove forests or swamps help stabilize shorelines, and they are also critical nurseries for fish, shrimp, and other commercial species
• Estuaries


  Bays where rivers empty into the sea, mixing fresh water with salt water
• Salt marshes


  Shallow wetlands flooded regularly or occasionally with seawater, occur on shallow coastlines, including estuaries
• Tide Pools


  Depressions in a rocky shoreline that are flooded at high tide but retain some water at low tide. These areas remain rocky where wave action prevents most plant growth or sediment (mud) accumulation
• Barrier Islands


  Low, narrow, sandy islands that form to parallel to a coastline. They occur where the continental shelf is shallow and rivers or coastal currents provide a steady source of sediments
• Freshwater Ecosystems


  • Vary according to depth and light penetration, which control size and types of vegetation
  • Often small but they are disproportionately important in biodiversity
• Vertical Zones in Freshwater Lakes

  • Benthos – the bottom, occupied by a variety of snails, burrowing worms, fish and other organisms
  • Epilimnion – a warmer upper layer that is mixed by wind and warmed by the sun
  • Hypolimnion – below the epilimnion. A colder, deeper layer that is not mixed
  • Thermocline – Sharp temperature boundary
  • Mesolimnion – below thermocline, the water is much colder
• Wetlands


  Shallow ecosystems in which the land surface is saturated or submerged at least part of the year. Have vegetation that is adapted to grow under saturated conditions
• Types of Wetlands

  • Swamps – Also known as wooded wetlands, wetlands with trees
  • Marshes – Wetlands without trees
  • Bogs – Areas of saturated ground, and usually the ground are composed of deep layers of accumulated, undecayed vegetation known as peat
  • Fens – Similar to bogs except that they are mainly fed by groundwater, so that they have mineral-rich water and specially adapted plant species
• Humans have become dominant organisms over most of the earth, damaging or disturbing more than half of the world's terrestrial ecosystems to some extent
• Humans preempt about 40 percent of the net terrestrial primary productivity of the biosphere either by consuming it directly, by interfering with its production or use, or by altering the species composition or physical processes of human-dominated ecosystems
• Conversion of natural habitat to human uses is the largest single cause of biodiversity losses