44.3 Terrestrial Biomes

The abiotic components of the environment are related to annual biomass production.

The net primary productivity of the environment with the greatest amount of biomass is maximized.
There is a warm and wet climate in these areas.
Photosynthesis can proceed at a high rate, enzymes can work most efficiently, and stomata can remain open without the risk of excessive transpiration; together, these factors lead to the maximal amount of carbon dioxide moving into the plant.
Habitat and food are important resources for other living things.
Dry and cold environments have lower rates of photosynthesis.
Animals living there will be affected by the decrease in food availability.

By the end of this section, you will be able to identify the two major abiotic factors that determine the landscape of the Earth.

The temperature and amount of precipitation of the eight major terrestrial biomes are different.
There are clues as to the importance of abiotic factors in the distribution of biomes by comparing the annual totals of precipitation and fluctuations in precipitation.

Predicting the geographic distribution of the biome and the vegetation type is dependent on temperature variation on a daily and seasonal basis.

The distribution of these biomes shows that they can be found in areas with similar climates.

The world's major biomes are distinguished by their temperatures and precipitation.

The mountains and polar ice are shown.

Plants with broad leaves fall and are replaced throughout the year in this biome.

The temperature and sunlight profiles of tropical wet forests are very stable, with the temperatures ranging from 20 to 34 degrees Centigrade.

The lack of seasonal temperature variation in the tropical wet forest is apparent when one compares it to other forest areas.
The lack of seasonal growth in the area leads to year-round growth of plants.
Tropical ecosystems don't have long days and short days during the yearly cycle.
A longer period of time for plant growth is provided by a constant amount of sunlight.

The annual rain in tropical wet forests varies from 125 cm to 660 cm.

The annual rainfall is highly variable.
There can be more than 30 cm (12 in) of precipitation in tropical wet forests in wet months and less than 10 cm ( 3.5 in) in dry months.
The driest month of a tropical wet forest still beats the annual rainfall of deserts.

Tropical wet forests have high net primary productivity because they are ideal for plant growth.

Plants with high species diversities can be found in the tropical wet forest.
Between 100 and 300 species of trees are present in a singlehectare of the South American Amazon rain forest.
One way to see this is to look at the horizontal layers.
There is a sparse layer of plants on the forest floor.
There is an understory of shrubs.
There are more trees emerging through the closed upper canopy.
The tropical wet forests are home to a variety of plants, animals, and organisms.

Epiphytes are found in the tropics.

The variety of plants and the structure of the tropical wet forests are used by many species of animals.
Some organisms live several meters above ground.

The forests along the Madre de Dios river, near the Amazon River, have high species diversity.

The Savannas are usually hot, tropical areas with an average temperature of 24 degC to 29 degC (75 degF to 84 degF) and an annual rainfall of 10-40 cm.
Savannas have an extensive dry season, which means that forest trees do not grow as well as they do in the tropical wet forest.
There are relatively few trees within the grasses and forbs that dominate the savanna.
Plants have evolved well-developed root systems that allow them to quickly grow again after a fire.

The Savanna in Taita Hills Wildlife Sanctuary is dominated by grasses.

In some years, the biome is very dry.
Subtropical hot deserts can have daytime soil surface temperatures between 60 and 140 degrees Centigrade and nighttime temperatures between 0 and 32 degrees Centigrade.
The lack of water is the main reason for this.
In cold deserts, the temperature can be as high as 25 degrees Centigrade and as low as -30 degrees Centigrade.

Subtropical deserts have low annual precipitation of less than 30 cm (12 in) with little monthly variation and lack of predictability.

In some cases, the annual rainfall can be as low as 2 cm in the desert areas of central Australia and northern Africa.

Low and unpredictable precipitation is related to the vegetation and low animal diversity.

Perennial vegetation that lives from one year to the next is absent in very dry deserts; instead, many plants are annuals that grow quickly and reproduce when rainfall occurs, and then die.
Many other plants in these areas have a number of adaptions that conserve water, such as deep roots, reduced foliage, and water-storing stems.
Seed plants in the desert can be in bloom for a long time between rains.
Desert animals have adapted to nocturnal behavior.

Many desert plants have no leaves at all.

The leaves of ocotillo (Fouquieria splendens), shown here in the Sonora Desert, are only visible after rain.

Most of the rain falls in the winter in the 65 cm to 75 cm range.

During the summertime, many chaparral plants are not active.
Nitrogen is rich in the ashes left behind after a fire.

shrubs dominate the chaparral.

Specific growing seasons for plants are created by the annual temperature variation.

It is possible for plants to grow when temperatures are warm enough to sustain plant growth and when there is enough water available.
Water, which is stored in the form of ice, is not available for plant growth during much of the winter.

The annual precipitation is between 25 and 75 cm.

There aren't many trees except for those found growing along rivers or streams because of the lower annual precipitation.
The vegetation is dense enough to sustain populations of animals.
The vegetation is dense and the soils are fertile because the roots and stems of the grasses are in the soil.
When plants die and decay, the roots and rhizomes act to anchor them into the ground and replenish the organic material in the soil.

The buffalo, also known as the American bison, is a mammal that used to populate American prairies.

When fire is suppressed, the vegetation becomes scrub and sometimes dense forests with tree species that are resistant to fire.
Control burns can be used to suppress the growth of trees and maintain the grasses.

This is found in the mid-latitude regions.

During cold winters, the temperature can be as low as -30 degC and as high as 30 degC.
The growing seasons of the forests have been defined by these temperatures.
Precipitation varies between 75 cm and 150 cm throughout the year.

Due to the moderate annual rainfall and temperatures, deciduous trees are the dominant plant in this area.

Deciduous trees don't have leaves in the winter.

During the winter season, there is no photosynthesis in the trees.
As the temperature increases, new leaves appear.
The net primary productivity of tropical wet forests is higher than that of temperate forests.
The diversity of tree species in the tropics is greater than in the temperate forests.

The dominant plant in the forest is Deciduous trees.

The trees of the temperate forests shade a lot of the ground, but they are not as tall as the trees in tropical wet forests.

The soils of the forests are rich in both organic and inorganic minerals.
The thick layer of leaf litter on forest floors does not develop in tropical rainforests.
As the leaf litter decays, the soil gets some of its vitamins and minerals.
The leaf litter protects the soil from erosion, insulates the ground, and provides habitats for invertebrates, such as the pill bug and the red-backed salamander.

There are cold, dry winters and cool, wet summers in this area.

The annual precipitation is from 40 cm to 100 cm and usually happens in the form of snow.
The cold temperatures cause little evaporation.

The long and cold winters have led to the predominance of cone-bearing plants.

These trees are evergreen and retain their leaves year-round.

Less energy from the sun is required to warm a needle-like leaf than a broad leaf, so evergreen trees can photosynthesize earlier in the spring.
In the boreal forest, evergreen trees grow faster than deciduous trees.
The soils in the forest regions are acidic.
A new set of nitrogen-rich structures must be produced by the trees each year.
The broad-leafed deciduous trees may have a competitive advantage over the coniferous trees that retain nitrogen-rich needles.

The net primary productivity of tropical wet forests is higher than that of boreal forests.

Slow-growing tree species are long-lived and accumulate a large standing biomass over time, which makes the above-ground biomass of boreal forests high.
In tropical wet forests, plant species diversity is higher than in temperate forests.
The forest structure seen in tropical wet forests is not found in boreal forests.
The structure of a forest is usually made up of a tree layer and a ground layer.
When conifer needles are dropped, they don't break as quickly as broad leaves, which means less nitrogen is returned to the soil to fuel plant growth.

There are low lying plants and trees in the boreal forest.

The north of the subarctic boreal forest is where the tundra is located.
The winter temperature is -34 degrees Centigrade and the summer temperature is 12 degrees Centigrade.
Plants in the tundra have a short growing season.

There are almost 24 hours of daylight during this time.

The annual precipitation of the tundra is very low.
Due to the cold temperatures, there is little precipitation.

Plants in the tundra are usually low to the ground.

There is little species diversity, low net primary productivity, and low above-ground biomass.
The inability of roots to penetrate deep into the soil is due to the slow decay of organic matter.
During the growing season, the ground of the tundra can be covered with plants.

shrub willow is a low-growing plant that dominates the landscape.

Desert, savanna, temperate forest, tropic, tundra are some of the biomes that can be explored further.