We will only take a cursory look at this chapter. Much of it you have probably studied before as biomes are covered in middle school science and high school geography. What we will study will be the factors causing a given land mass to become a desert or rainforest. The study of the biosphere (area of the Earth where life exists) is broken into large section of geographic land with similar climates known as biogeographical regions. Biogeographical regions are further divided into biomes, based on mature life forms (known as mature climax successional species, named after the process of succession). In large part, this chapter looks at the major biomes found on Earth.

Desert –

Characterized by little rainfall (less than 10 cm) and high evaporation. Deserts often display low species diversity compared to other biomes. Low humidity means these areas have few clouds so they also display extremes in temperature swings. Abiotic: low water, low humidity, extreme temperatures. Biotic: low primary productivity.

Grasslands –

Characterized by moderate rainfall and rich soils. Many grasslands have intermittent trees (savannas) but grasses and other nonwoody plants tend to dominate the climax community. This biome is the most threatened biome in the world – not the rainforest! Many grasslands are cultivated for agriculture or, when poorly managed, become deserts due to high ion levels in the soil or drainage of aquifers. Abiotic: moderate moisture, rich soils. Biotic: high productivity.

Temperate Deciduous Forests –

Temperate regions have seasons, and deciduous trees are those that loss their leaves over the winter. These forests dominate the east coast of America (oak, maple, hickory forests). High rainfall and seasonal temperature fluctuations are the abiotic factors influencing these forests.

Conifer Forest/Taiga-

Trees with cones, such as spruce, firs, pines, etc, characterize these biomes. The leaves are in needle form to protect from water loss and they often remain on the tree for years (this way, they are ready to collect light when the short growing season starts in the spring). These forests often have moderate rainfall, poor soils, and extreme seasons (exceptions do exist).

Tundra –

The tundra is basically a frozen desert. How can lakes and streams exist in a desert? The tundra has frozen soil (permafrost) that prevents the water that does fall from draining. The low temperatures and frozen soil reduce nutrient cycling, leaving extensive peat bogs (decomposing material).

Tropical Rainforest –

Extremely high rainfall and constant temperatures (tropical) make the rainforests an area of extreme biodiversity (probably the highest of any biome) where many plants compete for sunlight and many organisms compete for food. Nutrient cycling is extremely high in this biome (this is why the burn-n-abandon style of agriculture is observed in this area, the soils are quickly depleted of nutrients). Extremely high primary productivity!

Freshwater Biomes –

Most of the globe is covered with water, so we must consider aquatic biomes in our coverage of global segments of the biosphere. The levels of nitrogen and phosphorus are huge issues in freshwater ecology today. We have greatly altered the nutrient cycles for these molecules, resulting a great increase in productivity (and algae growth) in lakes. This is called eutrophication, or excessive growth of producers due to high nutrient levels. In contrast, oligotrophic waters are clear due to their lack of excess fertilizers.