Class Session 13> Biomass
Now, let’s turn our attention to the second major resource that we humans use, biomass. Biomass refers to living material, other than humans, and we use tremendous amounts of biomass for all kinds of things such as wood to build houses, plants for medicines, and chickens for food. Humans have used biomass down through the millennia to support themselves. The earliest hunting gathering societies ate wild game and collected wild plants.
What’s happening at this juncture in history is that as the number of humans has increased, so too the amount of the world’s biomass consumed by humans. Before we look at consumption of biomass and the types of impacts brought about by the current patterns of consumption, let’s first look at how the biosphere – the earth’s subsystem made up of all living things expect humans – is put together.
1. The Neighbors
No one really knows how many life forms humans share this planet with. Over the years, we've tried to classify the many plants and animals with which we've come in contact. The classification of plants and animals is known as taxonomy and taxonomists identify and name species. A species is a group of individuals that can successfully breed with one another, that share ties of common parentage and thus possess a common pool of genes. Similar types of species which cannot breed make up the next higher order, known as genus. The genus Vulpes, for example, contains several species of foxes. The next higher group is family, followed by order, class, phylum and finally kingdom. The five kingdoms are animals, plants, protoctists, bacteria and fungi. There are plenty of estimates, but no one really knows how many species there are. Estimates range from 13 to 118 million. Humans have identified and named around 2,756,000 species, somewhere between 2% to 20% of the total. Mostly what we’ve identified and named is the big stuff on land, such as mammals and birds.
You’ve heard the term, maybe even used it once or twice. But what does it mean? Let’s take a look. Ecology is the study of the interrelationships between living organisms and between living organisms and their surroundings. Ecology is broad in scope, comprising elements of many disciplines, yet specific in example. Here are some important ecological terms:
A. Population: The number of individual organisms that live together in the same location.
B. Habitat: The physical surroundings in which an organism lives, including elements of the atmosphere, lithosphere, hydrosphere and biosphere. It consists of a variety of factors including temperature, soil type, and moisture, but al so contains living plants and animals.
C. Niche: The role or function that an organism performs in its natural ecosystem, including its activities, resource use, and interactions with other organisms. Roles include the roles of predator (eats other animals) or prey (is eat en by other animals).
D. Ecosystem: The living (biotic) and non living (abiotic) components of an environment make up an ecosystem. The abiotic components of ecosystems include:
1. Light, which is a critical input to photosynthesis;
2. Moisture, all living things contain water; · salt, also a critical element to many ecosystems;
3. Temperature, which has a profound effect on the growth and well being of organisms;
4. Oxygen, both plants and animals use oxygen in the process of respiration, and;
5. Fire, which can also be included as a component of ecosystems.
E. Food Chain: The food chain represents the process by which stored solar energy is converted into useful energy and by which energy and nutrients flow through ecosystems. The food chain is the sequence of organisms through which energy and nutrients move. The food chain consists of several steps or levels. The first step is the conversion of solar radiation into chemical energy by plants. Plants accomplish this conversion through photosynthesis in which plants take in sunlight, water and carbon dioxide and produce glucose or sugar molecules and oxygen.
Plants utilize some of this energy for their own growth and metabolism. This "internal" use of energy is called respiration. The energy not used by plants during respiration is stored in the plant as glucose or sugar molecules. Plants are referred to as producers because they, in effect, produce the chemical energy which sustains other life forms.
Plants consume about 90% of the energy that they receive during respiration and they store about 10% of the energy they get from the sun. Energy from the sun is measured in calories. A calorie is the amount of energy required to raise the temp of 1 gram o f water 1 degree centigrade. Let's say that a certain plant receives 1,000 calories of solar radiation. Ninety percent of that energy is used by the plant during respiration and 10%, or 100 calories, is stored in the plant. When the plant gets eaten, 10% of the original 1,000 calories of solar radiation is consumed. So whatever organism eats the plant will receive 100 calories. This "primary" consumer, or herbivore, is considered to be the second step or level of the food chain.
Like plants, consumers utilize about 90% of the energy that they receive for their own metabolism and 10%, like plants, is stored in the tissue of the primary consumer. When the primary consumer gets eaten, by an organism known as a secondary consumer or carnivore, the secondary consumer receives 10% of the energy originally received by the primary consumer. In this case, the secondary consumer would receive 10 calories. Consumption of the primary consumer by the secondary consumer is the second step or level of the food chain. An organism called a tertiary consumer eats the secondary consumer. Again, 90% of the energy is consumed by the tertiary consumer and 10% is stored for passage to the next level consumer. Longer food chains involve quaternary and quinary consumers.
At the end of the food chain are the decomposers or detritus feeders which are extremely important because they feed on dead organic matter, breaking it down into inorganic and organic matter. The decomposers include fungi and bacteria and they break down living matter into back into chemicals and elements. Only six elements & compounds -- carbon, oxygen, hydrogen, nitrogen, phosphorus, and sulfur -- make up 97% of the mass of your body and more than 95% of the mass of all living organisms.
F. Biogeochemical Cycles – There are 92 naturally occurring elements on earth. Only about thirty percent, however, are found in living organisms. In addition to the six we've already mentioned -- carbon, oxygen, nitrogen, sulfur, phosphorus, and hydrogen -- the remaining elements necessary for the survival and good health of plants and animals are required only in relatively small or trace amounts. There is a fixed supply of these essential elements, and they are continuously cycled through the air, water, soil, plants, and animals and converted to useful forms by what are known as biogeochemical cycles (bio meaning "living," geo for water, rocks, and soil, and chemical for the matter changing from one form to another). A biogeochemical cycle, therefore, is a natural system of recycling the principal elements & compounds necessary to sustain life. The six major biogeochemical cycles are the carbon cycle, oxygen cycle, nitrogen cycle, sulfur cycle, phosphorus cycle, and hydrogen cycle.
G. Biological Communities - A biological community is a grouping or assemblage of interacting plants and animals on a shared site or habitat. Many thousands of community types exist on earth. There are, however, two principal types or categories of communities, terrestrial or land based communities and aquatic or communities found in or near water. Terrestrial communities include forests, grasslands, tundra and desert communities. Aquatic communities include marine or salt water and freshwater communities. The abundance of life within the different biological communities is closely linked to the environmental conditions of the community's habitat. In the case of forests, for example, both heat and water determine the abundance or density of forest ecosystems.
Due to tremendous amount of heat and moisture found at the equator, the world's most abundant forest ecosystems are tropical rainforests which contains the greatest number and type of plant, animal, protoctists, bacteria and fungi found on earth. Other tropical forests, characterized by locations which receive less warmth and rainfall include monsoon forests and tropical evergreen forests.
Above the tropics are the mid-latitudes. Only one forest type is found in the mid-latitudes, the temperate forest. Temperate or mid-latitude forests are characterized by broadleaf, deciduous trees which lose their leaves during certain portions of the year when water is not available because the ground is frozen. As a means of "shutting down" their transpiration systems, deciduous trees lose the surfaces from which they transpire, their leaves.
Above the temperature, mid-latitude forests are found the northern coniferous or taiga forests. Because the ground is frozen for a greater period of the year, conifers have greatly reduced transpiration surfaces. Instead of the broad leaves found in both tropical and temperate forests, coniferous trees have small, thin or needle leaves, hence the term needle-leaf trees.
Grasslands exist where there is insufficient moisture to support larger plants, like trees. The major types of grasslands, tall grass - prairie and savannah -- and short grass or steppe, exist in different locations as a result of the amount of moisture they receive. Grasslands and forests are both found in locations with sufficient warmth and moisture. The two remaining terrestrial communities, tundra and desert, are found in places with extreme climates. Tundra vegetation, which includes mosses, lichens and sedges, are found in polar and sub-polar climates and desert vegetation, or xerophytes, are found in places that are extremely dry.