We are halfway through our survey of biomes, having covered rainforest,
desert, grassland, and shrubland. Next up, we have the temperate deciduous forest.
These contain broadleaf trees like oaks, maples, and beeches; shrubs, perennial herbs,
and mosses. Temperate deciduous forests are most notable because they go through four seasons:
Winter, Spring, Summer, and Fall. Here, leaves change color, or senesce, in autumn,
fall off in the winter, and grow back in the spring. This adaptation allows plants to survive
cold winters. Temperate deciduous forests are located in mid-latitude areas which means that
they are found between the polar regions and the tropics. These deciduous forest regions
are exposed to warm and cold air masses, which cause them to experience four distinct seasons.
The temperature varies widely from season to season with cold winters, and hot, wet summers.
The average yearly temperature is about 10°C, but temperatures can reach highs of 30oC and lows of
-30oC. The areas in which deciduous forests are located get about 750 to 1,500 millimeters of
precipitation spread fairly evenly throughout the year. During the fall, trees change color
and then lose their leaves. This is in preparation for the winter season. Because it gets so cold,
the trees have adapted to the winter by going into a period of dormancy or sleep. They also
have thick bark to protect themselves from the cold weather. Trees flower and grow during the
spring and summer seasons. Many different kinds of trees, shrubs, and herbs grow in deciduous
forests. There are also several different kinds of plants like mountain laurel, azaleas,
and mosses that live on the shady forest floor where only small amounts of sunlight get through.
Continuing in our journey toward the poles, next we have the temperate evergreen forest.
Trees that produce cones and needles are called coniferous-evergreen trees. Some needles remain
on the trees all year long. Coniferous forest regions have cold, long, snowy winters, and warm,
humid summers, and therefore well-defined seasons, with at least four to six frost-free months.
The coniferous forest is sandwiched in between the tundra to the north and the deciduous forest
to the south. One type of coniferous forest, the northern boreal forest, is found in 50° to 60°N
latitudes. Another type, the temperate coniferous forests, grow in lower latitudes of North America,
Europe, and Asia, in the high elevations of mountains. Coniferous forests consist mostly
of conifers, which are trees that grow needles instead of leaves and cones instead of flowers, as
we remember from the botany series. Conifers tend to be evergreen, meaning that they bear needles
all year long. These adaptations help conifers survive in areas that are very cold or dry. Some
of the more common conifers are spruces, pines, and firs. Precipitation in coniferous forests
varies from 300 to 900 millimeters annually, with some temperate coniferous forests receiving up to
2,000. The amount of precipitation depends on the forest’s location. In the northern boreal forests,
the winters are long, cold, and dry, while the short summers are moderately warm and
moist. In the lower latitudes, precipitation is more evenly distributed throughout the year.
Lastly, as we continue to more polar latitudes, we arrive at the tundra. Almost no trees can be found
in tundra environments due to the short growing season. Instead we find lichens, mosses, grasses,
sedges, and shrubs. Examples of tundra include regions south of the Arctic ice caps and extending
across North America, Europe, and Siberia. The tundra is the coldest of all the biomes. It also
receives low amounts of precipitation, making the tundra similar to a desert. Much of Alaska
and about half of Canada are categorized as a tundra biome. Tundra is also found at the tops
of very high mountains elsewhere in the world. Temperatures are frequently extremely cold,
but can get warm in the summers. Tundra winters are long, dark, and cold, with mean temperatures
below 0°C for six to ten months of the year. The temperatures are so cold that there is a
layer of permanently frozen ground below the surface, called permafrost. This permafrost is
a defining characteristic of the tundra biome. In the tundra summers, the top layer of soil
thaws only a few inches down, providing a growing surface for the roots of vegetation. Precipitation
in the tundra totals to 150 to 250 millimeters a year, including melted snow. That's less than
most of the world's deserts. Still, the tundra is usually a wet place because the low temperatures
cause evaporation of water to be slow. Much of the arctic has rain and fog in the summers,
as melted ice water gathers in bogs and ponds. Vegetation in the tundra has adapted to the cold
and the short growing season by remaining small in size, growing close to the ground, and developing
fuzzy textures to shield from the wind and frigid temperatures. While few trees grow in the tundra,
again due to the permafrost, those that do manage to grow stay close to the ground so they
are insulated by snow during the cold winters. And with that we have covered the major types
of terrestrial biomes. Now that we know the settings in which plants and animals live,
we will be better suited to learn about how they interact, so let’s move forward and do just that.