The structure of forest ecosystem is an interconnected hierarchy of plants, animals, microbes, soil, air, water, and the interactions between these components.
Some models can be used to describe the structure of forest ecosystem, such as; food chain, food web, and energy pyramid.
This article discusses the structure of forest ecosystem based on models, components, processes; as outlined below;
Models of the Structure of Forest Ecosystem
Three models of the structure of forest ecosystem are; food chain, food web, and energy pyramid.
1). Food Chain as a Model of the Structure of Forest Ecosystem
The food chain is a linear representation of the order or sequence of energy transfer in an ecosystem, based on the feeding relationships between various groups of organisms.
There are other systems or diagrams used to represent the transfer of bioenergy in ecosystems. However, food chains are unique for being simplified.
Unlike most systems, the food chain shows energy transfer as a simple, linear hierarchy with producers at the bottom, and apex predators at the top.
Also, in food chains, energy transfer is expressed strictly in terms of food and feeding relationships or patterns. Food chains are also concerned with only the biotic (living) components of the ecosystem.
Based on feeding patterns, the organic groups in a food chain can be differentiated into autotrophs (producers) and heterotrophs (consumers).
Autotrophs are organisms that can produce their own food independently, using sunlight, carbon dioxide and water, in a process known as photosynthesis . These organisms are equipped with a green pigmentation called chlorophyll, and examples include green plants, microalgae and cyanobacteria.
Heterotrophs are organisms that are unable to produce their own food, and therefore depend on autotrophs (directly or indirectly) for their survival .
These organisms include mammals, reptiles, amphibians, birds, fish, annelids, and insects.
The food web starts from the autotrophs, who are responsible for introducing food into the ecosystem. Above the autotrophs are the heterotrophs, whose feeding patterns include herbivorous, carnivorous, parasitic, mutual and commensal feeding.
2). Food Web as a Model of the Structure of Forest Ecosystem
Food web is a representation of the pathways through which biomass is transferred in an ecosystem.
Like the food chain, food webs show energy transfer in the form of food, and feeding relations between organisms. The food web is also mainly concerned with biotic or living components of the ecosystem.
Difference between food web and food chain is that a food chain shows singular pathways of energy transfer, while food web shows multiple pathways, or multiple food chains. A food web is made up of interconnected food chains . It can also be described as a network of food chains.
Unlike food chains which are highly simplified, food webs show the complex interconnections between the lifecycle and feeding habits of various groups of organisms in an ecosystem.
3). Energy Pyramid as a Model of the Structure of Forest Ecosystem
Energy pyramid is a hierarchical representation of the levels and processes of energy transfer in an ecosystem .
Also known as the ecological pyramid, this model is made up of a series of trophic levels that represent the various groups of organisms according to their feeding habits. The pyramid is arranged so that these trophic levels are placed in their correct positions in the feeding hierarchy.
There are often four trophic levels in an energy pyramid, although this number may be five in some cases.
The lowest level (level 1) is occupied by primary producers, which include plants and other organisms that have chlorophyll pigmentation.
Tropic level 2 is occupied by primary consumers, which feed directly on plants.
Secondary consumers occupy trophic level 3. These organisms feed on the primary consumers.
Tertiary consumers, which occupy trophic level 4, can feed in both primary and secondary consumers.
(In energy pyramids that have only four levels, the tertiary consumers are at the top of the pyramid, and can feed on primary producers, primary consumers and secondary consumers. On the other hand, in pyramids with up to five levels, the tertiary consumer feeds on other consumers (primary and secondary), but not on primary consumers.
Trophic level five is occupied by Apex Predators, that feed on organisms in all other levels of the pyramid.
Decomposers such as bacteria and fungi, can occur at any of the trophic levels, since they feed through the process of biodegradation, of both plant and animal organic matter. However, they are often placed at the topmost level of the pyramid.
The energy pyramid is different from food web and food chain because it is concerned mainly with energy transfer, and may not always prioritize feeding relationships.
It is also more detailed than food web or food chain, because it outlines organisms, feeding relations, trophic levels, and biological processes. In both food chain and food web, the only biological process that is highlighted is feeding or nutrition.
Components of the Structure of Forest Ecosystem
Components that make up the structure of forest ecosystem are; organisms and trophic levels.
These components are discussed below according to the three models.
1). Based on the Food Chain Model
Based on the food chain model, the forest ecosystem has a linear structure. This structure represents the order or sequence of a singular pathway of energy transfer through feeding, in a forest.
An example of a food chain in the forest ecosystem is outlined below;
-Level 5: Mongoose feeds on snake
-Level 4: Snake feeds on chameleon
-Level 3: Caterpillar is consumed by chameleon
-Level 2: Caterpillar feeds on plant for its survival
-Level 1: Plant produces its own food (through photosynthesis, from solar energy, CO2 and water)
2). Based on the Food Web Model
The structure of the forest ecosystem based on the food web model, is interconnected.
It occurs as a network of chains or linear sequences which intersect with each other at some points. This structure shows how biodiversity in forests leads to cyclic and complex energy transfer relations.
In a food web, there are no distinct levels. Organisms at any trophic level may link to organisms at other levels, at some point in their feeding and energy transfer activities.
A simple food web in a forest ecosystem is explained below;
-Level 4: Leopard, owl, hawk
-Level 3: Fox, toad, civet, mongoose
-Level 2: Deer, rabbit, locust, fish
-Level 1: Algae, plants
Sequences and Relationships
–Owl, hawk, feed on toad
–Owl, hawk, feed on fish
–Leopard feeds on deer
–Fox, civet, mongoose, hawk, owl, feed on rabbit
–Deer, locust, rabbit, feed on terrestrial plants
–Fish feeds on algae, aquatic plants
–Algae and plants produce food through photosynthesis
The food web is unique because it does not oversimplify the energy transfer or feeding sequence in a forest. Rather, it shows that energy can be directly transferred between any two trophic levels, depending on the organisms involved.
3). Based on the Energy Pyramid Model
Based on the energy pyramid, the structure of forest ecosystem is a hierarchical polygon.
The components of the forest are grouped into trophic levels, which represent their position in the hierarchy of energy transfer.
Energy pyramid is concerned mainly with how energy is conveyed from one level to another, in the ecosystem. It also takes into account the energy losses that occur in the process.
Typically, about 90% of available energy is lost as heat between one trophic level and the overlying one . This means that only about 10% of energy is successfully conveyed or transferred.
The following is a simple illustration energy transfer across the trophic levels and components of the energy pyramid in a forest ecosystem;
-Level 5: Apex Predators/Omnivores; available energy= 0.1KJ
-Level 4: Tertiary Consumers/Large Carnivorous Heterotrophs (Leopard, wolverine, lynx); available energy: 1KJ
-Level 3: Secondary Consumers/Carnivorous Heterotrophs (fox, civet, mongoose, hawk) available energy= 10KJ
-Level 2: Primary Consumers/Herbivorous Heterotrophs (deer, rabbit); available energy= 100KJ
-Level 1: Primary Producers/Autotrophs (plants, algae, cyanobacteria); available energy= 1000KJ
Processes of the Structure of Forest Ecosystem
Processes that contribute to the structure of forest ecosystem are; photosynthesis, feeding, nutrition, and biodegradation.
These processes are discussed below according to the three models.
1). Based on the Food Chain and Food Web
The only biological process which is highlighted in the food chain and food web is feeding.
This means that the structure of forest ecosystem is defined by feeding relations, when it is based on the food chain or food web.
To move from one level or point in a food chain or food web, to the next, some form of feeding must occur. This may be herbivorous, carnivorous, or omnivorous.
Although feeding is the most prominent process that is highlighted by these models, photosynthesis and biodegradation are also important. These two processes mark the beginning and end points of a feeding sequence respectively.
2). Based on the Energy Pyramid Model
When we define the structure of forest ecosystem based on the energy pyramid model, there are various processes involved. These include photosynthesis feeding, nutrition, and biodegradation.
Photosynthesis occurs at trophic level 1; and is carried out by primary producers, or plants (mainly trees). It is the process that introduces energy into the forest ecosystem.
Feeding and nutrition occur from trophic levels 2 to 4 (or 5). It is carried out by primary, secondary and tertiary consumers. In energy pyramids with five levels, the apex predators (which occupy the last or topmost level) also carry out feeding and nutrition.
It is important to note that feeding and nutrition are similar yet different processes. Feeding is the act of consuming food, energy or biomass; while nutrition is the process of assimilating and utilizing the consumed resources .
Biodegradation can occur at any of the trophic levels of the energy pyramid in a forest ecosystem. It is the process by which biomass or organic matter is broken down by microorganisms to form simple minerals that are released back into the environment.
Role of Environmental Factors in the Structure of Forest Ecosystem
Aside living organisms and biological processes, other factors also play a role in the structure of the forest ecosystem.
These are the abiotic, non-living or environmental factors. Examples of such factors include soil, water, air, geographic and physicochemical conditions.
Soil, water and air quality affect the structure of the forest ecosystem by determining the effectiveness of biological processes and the survival of living organisms.
Poor quality of soil, air and water will disrupt the natural flow of energy in the food chain, food web and energy pyramid, and therefore will crumble the structure of the forest ecosystem.
Some natural functions of forest ecosystem include soil conservation, water conservation and air purification. Through these functions, forests are able to naturally maintain their biological and chemical structure.
The physical structure of forest ecosystem is affected by geographic and physicochemical conditions like topography, climate, drainage, salinity, oxygen, and pH.
These conditions can affect the vegetation, animal biodiversity, and feeding relationships in the forest.
The structure of forest ecosystem is a hierarchical interconnected structure comprising of organisms, processes, food chains, food webs and energy pyramids.
Components that make up the forest ecosystem structure are primary producers, primary, secondary and tertiary consumers, decomposers, geographic conditions, physicochemical factors and biological processes.
1). Barbier, M.; Loreau, M. (2019). “Pyramids and cascades: a synthesis of food chain functioning and stability.” Ecology Letters 22(2). Available at: https://doi.org/10.1111/ele.13196. (Accessed 8 August 2022).
2). Crane, K. W.; Grover, J. P. (2009). “Coexistence of mixotrophs, autotrophs, and heterotrophs in planktonic microbial communities.” Journal of Theoretical Biology 262(3):517-27. Available at: https:://doi.org/10.1016/j.jtbi.2009.10.027. (Accessed 8 August 2022).
3). Mathers, R. (2017). “Food Webs, Boxicity and Trophic Status.” Available at: https://doi.org/10.13140/RG.2.2.23565.54240. (Accessed 8 August 2022).
4). Panawala, L. (2017). “Difference Between Autotrophs and Heterotrophs.” Available at: https://www.researchgate.net/publication/314838354_Difference_Between_Autotrophs_and_Heterotrophs. (Accessed 8 August 2022).
5). Pich, J.; Brage, L. B.; Thomas, M.; Canals, R.; Tur, J. A. (2011). “Assimilating and following through with nutritional recommendations by adolescents.” Health Education Journal 70(4):435-445. Available at: https://doi.org/10.1177/0017896910379695. (Accessed 8 August 2022).
6). Trussell, G. C.; Matassa, C. M.; Ewanchuk, P. J. (2017). “Moving beyond linear food chains: Trait-mediated indirect interactions in a rocky intertidal food web.” Proceedings of the Royal Society B: Biological Sciences 284(1851). Available at: https://doi.org/10.1098/rspb.2016.2590. (Accessed 8 August 2022).