Obviously you can’t know everything about the living world! No one does and who knows how long that exam would be! So we’ve condensed it down into the bits that you do need to know – phew.
The world has many communities of plants and species, these are known as ecosystems. And although they are diverse in nature they also share many common characteristics. These primarily relate to the climate and soil seen in the ecosystem. Climate, soils and vegetation interact closely to produce the characteristic nature of an individual ecosystem.
Ecosystems can be split into two main sections, abiotic and biotic elements. Abiotic elements are those that are non-living, but affect the ecosystem. Examples of these include water, heat, relief, the atmosphere, soil, fire, gravity, nutrients and rocks. Biotic elements are those living elements of the ecosystem. In other words the plants and animals.
Within the biotic element there are organisms which are known as producers. These convert sunlight into energy through the process of photosynthesis. There are also organisms known as consumers, which feed on the other organisms. Within each ecosystem there is a hierarchy of producers and consumers.
Basics covered, now we’re going to take a closer look at biomes. A biome is a community of plants and animals that have common characteristics for the environment they exist in.
There are eleven major biomes in the world, each influenced in their characteristics by their location and climate. These biomes are tundra, coniferous woodland (also known as taiga), tropical rainforest, tropical deciduous woodland, temperate deciduous woodland, mountains, tropical grassland (also known as savanna), temperate grassland, desert, chaparral and tropical scrub grassland.
Let’s look at some examples to help illustrate – this is going to be a lot of talking about trees – not the most thrilling I know, but it has to be done.
Coniferous woodland for example would be a biome that sees warm summers and very cold winters.
The temperature of coniferous woodland areas in the summer varies between 12 and 18oC, with temperatures falling below freezing for the winter months. In Northern forests, or those at high latitude, the temperature can remain below freezing for up to six months. Rainfall is low, with the majority falling in the summer. Snow can be expected in the winter months. The total precipitation amount will be approximately 500mm. Long summer days mean that the growing season, although short, can be productive.
The main soil found in coniferous forests is called a Podsol. This has a thin top layer of organic material, and is a very acidic soil. Snowmelt and summer rainwater leach the minerals in the soil (leaching), meaning that they are washed deeper into the soil, thus making it less fertile. The leached minerals, such as iron, concentrate in the B Horizon of the soil creating a hardpan. The acidic soil means that there are very few earthworms, which are very useful for mixing the soil.
Coniferous trees are evergreen, meaning that they have leaves all year round, and therefore can always photosynthesise. The trees of coniferous woodland, such as fir and pine, are very similar in shape. They are conical shaped, which allows snow to easily slide off them. The leaves are actually needles, which are the most efficient leaf for these trees.
The needles allow very little water loss by transpiration, which is particularly important in the relatively dry winter months. The trees of coniferous woodland are often of only one species and pack quite tightly together; meaning little light reaches the forest floor. Consequently there is little vegetation below the trees.
Coniferous trees are softwoods, and grow rapidly compared to deciduous trees. For this reason they are extensively used as timber and for paper making. Managed forestry of coniferous area is increasingly becoming a viable economic activity, although you have to wait a number of years until the trees are ready to be sold.
In contrast a biome with warm summers and relatively cold winters could be deciduous woodland.
Deciduous woodland ecosystems are found in areas where the summer temperatures range between 15 and 20oC, whilst the cool winters don’t generally drop below zero. Rainfall is moderate, usually between 1000 and 1500mm, and it falls throughout the year. The good summer temperatures and long days mean that the ecosystem is a very productive one.
The typical soil of British deciduous woodland is a brown earth. This is a reasonably fertile, mildly acidic soil. Some leaching occurs, and earthworm activity helps to mix up the soil. Leaves decompose slowly and add to the humus on the top layer of the soil.
Deciduous trees are ones that drop their leaves in the autumn. This large leaf fall helps to create fertile material on the forest floor. The trees of the woodland are species such as oak, ash, birch and maple.
They are typically about 20 to 30m high and form the top layer of the forest canopy. Below them on the forest floor, smaller trees and shrubs, such as holly, grow up.
This very much depends on how much light is allowed through to the forest floor. Below this shrub layer a third ground layer is found. This consists of plants such as brambles and bracken that take up the bottom meter of the forest layers.
Large tracts of deciduous woodland have been cleared across Britain over the past centuries, as humans have cut the trees down for building materials and fuel. Settlements were built close to woods, as they allowed local people a place to hunt, find fuel, and find protection in times of danger.
Also, one of the primary reasons for the clearance of many of the deciduous woodlands around Britain was to use the area for agriculture. This occurred as more and more new settlements grew and the food sources of the forests ran out.