ENVS Chapter 5 Pt 1

We call large biological communities biomes. If we know the range of temperature and precipitation in a particular place, we can generally predict what kind of biome is likely to occur there. An important characteristic of each biome is its biodiversity, or the number and variety of different biological species that live there.

Biome type can be predicted based on the temperature and precipitation found in an area.

Biomes Vary with Latitude -- Many temperature-controlled biomes occur in latitudinal bands. A band of boreal (northern) forest crosses Canada and Siberia. Tropical forests occur near the equator. Expansive grasslands lie near—or just beyond—the tropics. Many biomes are even named for their latitudes: like tropical rainforests or arctic tundra.

Tropical Rainforests – Tropical rainforests occur where rainfall is abundant—more than 200 centimeters (80 inches) per year— and temperatures are warm to hot year-round.

Tropical Savannas and Grasslands Are Dry Most of the Year -- Where there is too little rainfall to

support forests, we find open grasslands or grasslands with sparse tree cover, which we call savannas.

Deserts Are Hot or Cold, but Always Dry -- Deserts occur where precipitation is uncommon and

slight, usually with less than 30 centimeters of rain per year.

Temperate Grasslands Have Rich Soils -- As in tropical latitudes, temperate (midlatitude) grasslands occur where there is enough rain to support abundant grass but not enough for forests.

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Temperate Scrublands Have Summer Drought -- Often, dry environments support drought-adapted shrubs and trees, as well as grass. These mixed environments can be highly variable. They can also be very rich biologically. Such conditions are often described as mediterranean scrub or in California, chaparral. Evergreen shrubs with small, leathery leaves form dense thickets. Scrub oaks, drought-resistant pines, or other small trees often cluster in sheltered valleys. 1

Temperate Forests Can Be Evergreen or Deciduous -- These forests are grouped by tree type,

broad-leaved deciduous (losing leaves seasonally) or evergreen coniferous (cone-bearing).

Deciduous Forests -- Broad-leaf forests occur throughout the world where rainfall is plentiful. In mid-latitudes, these forests are deciduous and lose their leaves in winter. The loss of green chlorophyll pigments can produce brilliant colors in these forests in autumn. At lower latitudes, broad-leaf forests may be evergreen or drought-deciduous. Southern live oaks, for example, are broad-leaf evergreen trees.

Coniferous Forests -- Coniferous forests grow in a wide range of environmental 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. Thin, waxy leaves (needles) help these trees reduce moisture loss.

Temperate Rainforests -- The 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 Forests Lie North of the Temperate Zone -- Because conifers can survive winter cold, they tend to dominate the boreal forest. Dominant trees are pines, hemlocks, spruce, cedar, and fir. Boreal forests are found in Siberia, Canada, and the western United States.

Tundra Can Freeze in Any Month -- Tundra is a treeless landscape where temperatures are below freezing most of the year. It occurs at high latitudes or on mountaintops and has a growing season of only two to three months.

5.2 Marine Ecosystems -- Most marine communities depend on photosynthetic organisms. Phytoplankton: tiny, free-floating photosynthetic algae often support a marine food web rather than trees or grasses. In oceans, photosynthetic activity tends to be greatest near coastlines, where nitrogen, phosphorus, and other nutrients wash offshore and fertilize primary producers.

Deep-Sea Thermal Vent Communities -- Deep-sea thermal vent communities are another remarkable type of marine system. These communities are based on microbes that capture sulfur compounds released from thermal vents on the ocean floor.

Tidal Shores Support Rich, Diverse Communities -- Coral reefs are among the best-known marine

systems, because of their extraordinary biological productivity and their diverse and beautiful organisms.

Tidal Shores Continued: Mangroves -- Mangroves are a diverse group of salt-tolerant trees that grow along warm, calm marine coasts around the world.

Tidal Shores Continued: Estuaries & Salt – Marshes Estuaries are 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.

Tidal Shores Continued: Tide Pools -- Tide pools are depressions in a rocky shoreline that are flooded at high tide, but retain some water at low tide.

5.3 Freshwater Ecosystems -- Freshwater environments are far less extensive than marine environments, but they are centers of biodiversity. Most terrestrial communities rely, to some extent, on freshwater environments. In deserts, isolated pools, streams, and even underground water systems support astonishing biodiversity as well as provide water to land animals.

Wetlands Are Described by Their Vegetation -- Swamps are wetlands with trees. Marshes are

wetlands without trees. Bogs are areas of water-saturated ground usually composed of deep layers of undecayed vegetation known as peat.

Streams and Rivers Are Open Systems -- Streams form wherever precipitation exceeds evaporation and surplus water drains from the land. As streams collect water and merge, they form rivers. Ecologists consider a river system to be a continuum of constantly changing environmental conditions and community inhabitants from the headwaters to the mouth of a drainage or watershed.

5.4 Biodiversity -- Biodiversity, the variety of living things. Three kinds of biodiversity are essential to

preserve ecological systems and functions:

• genetic diversity is a measure of the variety of versions of the same genes within individual species.

• species diversity describes the number of different kinds of organisms within a community or ecosystem.

• ecological diversity refers to the richness and complexity of a biological community.