The function, structure and major components of Forest Ecosystem

Whittaker (1962) suggested that "An ecosystem is a functional system that includes an assemblage of interacting organisms (plants, animals, and saprobes) and their environment, which acts on them and on which they act".

Woodbury proposed in 1954 “an ecosystem is a complex in which habitat, plants, and animals are considered as one unit, the materials, and energy of one passing in and out of the other”.

Turk (1988) defined, as “an ecosystem is a system formed by the interactions of a variety of individual organisms with each other and with their physical environment.

The well-accepted definition of the ecosystem is “an interaction between the living organisms (biotic components) with the non-living matters (abiotic components) at which the exchange of materials in the form of energy takes place.

What is a Healthy Ecosystem?

Utilitarian Concept: If the ecosystem supplies a sustainable level of goods and services.

Ecological Concept: If the structure, function, complexity, interactions, and pattern of change are not altered.

The term ecosystem was suggested by an English ecologist Tansley (1935) and defined as "not only the

organism-complex but the whole complex of physical factors forming what we called the environment".

F.E. Clements (1916) recognized three types of interactions within the ecosystem.

1. The effects of the physical environment on organisms.
2. The effect of organisms on their physical environment 
3. The effect of organisms on organisms.

He termed type (1), (2), and (3) interactions as ‘action’, ‘reaction’, and ‘co-action’ respectively. There is a complex relationship between the structure and function of an ecosystem. Ecosystems are not static. They change over time, structurally, and functionally.

Ecosystem Characteristics (attributes)

1. Structure:
• Vertical: Trees, sapling, shrubs, herbaceous
• Horizontal: Uniform, patchy, random
2. Function: Constant exchange of matter and energy between the physical environment and living community
3. Complexity:
• All events and conditions are determined by multiple factors.
• Prediction of an event requires detailed knowledge of these factors and how they interact?
4. Interdependency: Behavior of the whole ecosystem is not predictable by the behavior of anyone part of the system considered separately
5. Temporal change: 
• The ecosystem is "not static"
• Changes are made within certain bounds, key processes and potentials are maintained.
6. Diffuse boundaries:
1. Clear boundaries between ecosystems are rare.
2. Ecosystems transition from one type to another.

Structure of an Ecosystem

An ecosystem has two components. They are abiotic and biotic components:

Abiotic Component

The physical environment is the biotic component. It comprises climatic conditions and elements and compounds of soil and atmosphere. The physical environment influences not only the ‘biotic structure’ but also the ‘function’ of the ecosystem. It controls structure by limiting the range of organisms that will be represented in the community of the ecosystem. The kind and degree of interaction between the population of various organisms and the physical environment determine the function of an ecosystem.

Biotic Components

Living components of the ecosystem are the biotic components. It comprises autotrophic organisms, heterotrophic organisms, and decomposers.

The function of an Ecosystem

The three functional characteristics of an ecosystem are energy flow, nutrients cycling, and ecosystem regulation.

1. Energy flow: To sustain the life processes all organisms need energy. The initial source of energy is the sun. Green plants directly use solar radiation to convert carbon dioxide from the atmosphere and water from the soil into glucose. This process is known as photosynthesis in which light energy converts into chemical energy. This energy is transfer to herbivores who consume plant biomass as a food and in turn herbivores to carnivores. The micro-organisms obtain energy from dead plants and animals. These transfers of energy are not cent percent effective. According to the second law of thermodynamics, in any transfer of energy from one form to another some energy escapes from the system, usually as heat. These series of energy transfers are regarded as the food chain or energy flow as they form a series of links.
2. Nutrient Cycling: The ecosystem draws nutrients from the atmosphere and soil. Simple inorganic elements converted into complex organic substances during biological processes, which are taking place in green plants. These complex organic substances from plant and animal tissues. When plants and animals die, tissues undergo bacterial decay and decomposition. Bacterial decay and decomposition of complex organic matter release inorganic nutrient elements to the physical environment and interns from the physical environment to plants. These continuous cycling of nutrients between plants to the physical environment and physical environment to plants are known as nutrient cycling.

   

   Nutrient Recycling
   

3. Ecosystem Regulation: The third functional characteristic is eco-regulation, i.e. the manner in which an ecosystem regulates itself. There are two ways in which an ecosystem can regulate itself. Interactions within the system, and interactions with other systems. Interactions within the system are four kinds: Competition between the individuals of one population, interspecific competition, interspecific cooperation, and interaction of leaving components with the abiotic environment. The competition between the individuals of one population does not change the composition of an ecosystem. The competition only controls the number of individuals in any one kind of organism. The interspecific, however, eliminates weaker species and change the composition of the ecosystem which is known as succession. Succession takes place between plant communities over time as a result of their interaction with the environment. The climax is the last stage of succession, it is more stable than the pioneer stage because of its greater diversity, larger organic structure, and a more balanced flow of energy.

The important point about succession, from the management point of view, is that though a climax community is more stable and more diverged, its net production is low. Production is mostly consumed by respiration. To secure more net production to harvest, man needs succession stages.

The last kind of interaction within the system is interspecific cooperation. Interspecific interaction is not always negative. It is often positive. Three forms of positive interaction have been recognized which are as such:

Commensalism, in which one population benefits another, but is not affected itself with the interaction; Photo operation, in which two populations benefit each other, but are not essential to each other for survival; Mutualism, in which association of two populations is vital for the existence of other. All ecosystems are open systems, i.e., they are not independent and interact with each other. The output from one ecosystem becomes the input to another ecosystem. In reality, therefore, an ecosystem is the input of the environment, the system itself, and the input environment

which is shown in the equation below.

I + S + O = Ecosystem,

Where I is an input environment, S is a system, O is an output environment.

The true understanding of the ecosystem requires knowledge of not only its internal dynamics, such as energy flow, recycling of materials, and organization of food webs but also its external dynamics, i.e. how the system exchanges energy and materials with other systems.

Components of Forest Ecosystem

Abiotic components: Soil, moisture, air, sunlight, chemicals

Biotic components:

Producer: Green plants (floating, suspended, rooted)

Consumer:

• Primary consumer: larva of frog, small fish
• Secondary consumer: big fish, crab, snake
• Tertiary consumer: waterbirds

Decomposer: Bacteria, fungi