TOPICS TO BE DISCUSS ON:
1. WHAT IS ECOSYSTEM
2. CHARCTERISTICS OF FOREST ECOSYSTEM
3. LAWS & PRINCIPLES GOVERNING THE FOEST ECOSYSTEM
4. NUTRIENT CYCLING IN A FOREST ECOSYSTEM
5. ENERGY TRANSFER IN A FOREST ECOSYSTEM
WHAT IS AN ECOSYSTEM?
An ecosystem is a community of living organisms (biotic components) in conjunction with the non-living components (abiotic components- air, water and mineral soil) of their environment interacting as a system. These biotic and abiotic components are said to be linked together through nutrient cycles and energy flows. As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment, they can be of any size but usually encompass specific, limited spaces (although some scientists say that the entire planet is an ecosystem) . Energy, water , Nitrogen and soil minerals are other essential abiotic components.
According to the Convention on Biological Diversity, an ecosystem is defined as a dynamic complex of plants, animals and micro-organism communities and their non-living environment that interact with each other and with air, water and soil.
Ecosystem are controlled both by external and internal factors. External factors such as climate, the parent material that forms the soil and topography control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem.
Ecosystem are dynamic entities-invariably they are subjected to periodic disturbances and are in the process of recovering from past disturbance. Ecosystem in similar environment that are located in different parts of the world can have very different characteristics because they contain different species. The introduction of non-native species can cause substantial shifts in ecosystem functions. Internal factors do not only control ecosystem processes but are also controlled by them. While the resource inputs are generally controlled by external processes like climate and parent materials. The availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Ecosystems include deserts, forests, mountains, wetlands, riparians (rivers and streams) and agricultural landscapes.
ABIOTIC FACTORS BIOTIC FACTORS
Sunlight Primary producers
Temperature Herbivores
Precipitation Carnivores
Water Omnivores
Soil Detritivores.
FOREST ECOSYSTEM
The entire assemblage of organisms (trees, shrubs, herbs, bacteria, fungi, and animals, including people) together with their environmental substrate (the surrounding air, soil, water, organic debris, and rocks), interacting inside a defined boundary. It is a natural woodland unit consisting of all plants, animals and micro organisms [biotic components] in that area functioning together with all of the non-living physical (abiotic) factors of the environment. The forest ecosystem is very important. Forests and woodlands occupy about 38% of the Earth's surface, and they are more productive and have greater biodiversity than other types of terrestrial vegetation. Forests grow in a wide variety of climates, from steamy tropical rainforests to frigid arctic mountain slopes, and from arid interior mountains to windy rain-drenched coastlines. The type of forest in a given place results from a complex of factors, including frequency and type of disturbances, seed sources, soils, slope and aspect, climate, seasonal patterns of rainfall, insects and pathogens, and history of human influence. Usually the canopy of the tallest trees forms the upper ecosystem boundary, and plants with the deepest roots form the lower boundary. The horizontal structure is usually described by how individual trees, shrubs, herbs, and openings or gaps are distributed. Forested ecosystem have great effects on the cycling of carbon, water and nutrients and these effects are important in understanding long-term productivity.
CHARACTERISTICS OF A FOREST ECOSYSTEM
The following are the basic features that could be seen in a forest ecosystem:
1. FOREST CANOPY: The forest canopy is an important feature of a forest ecosystem. It pertains to the top portion of a community of trees or plant crowns. A forest canopy serves as the interface between the atmosphere and the land. The canopy is also the upper habitat for other biological organisms in a forest ecosystem. It is mostly composed of large trees. The structure of forest canopy is not the same in every forest ecosystem because it depends on the availability of nutrients, tree arrangement and differences in biological species. More than half of the plants species are found in a forest ecosystem, so the biodiversity is greatest in the forest canopy. Most organisms are able to survive in the forest canopy because it is directly exposed to sunlight and rainwater.
2. FOREST FLOOR: The forest floor is the most distinct feature of a forest ecosystem. It is composed of fallen leaves, stems, twigs, branches and bark on the surface of the soil. A forest floor also contains organic and in organic substances. Many living organisms, such as the fungi, bacteria and other microorganisms, inhabit the forest floor. It is rich in nutrients and mineral contents. The forest floor has a significant role in the transfer of nutrients in the life cycle of the forest ecosystem. Most of the carbon and energy from the forest ecosystem is added to the forest floor over time. The majority of nutrients of the forest ecosystem comes from the forest floor due to the decomposition of organic substances.
3. MACRO ORGANISMS
Vertebrates: Forest animals are the consumers in forest ecosystems. They influence the flow of energy and cycling of nutrients through systems, as well as the structure and composition of forests, through their feeding behavior and the disturbances that they create. In turn, their abundance and diversity is influenced by the structure and composition of the forest and the intensity, frequency, size, and pattern of disturbances that occur in forests. Forest vertebrates make up less than 1% of the biomass in most forests, yet they can play important functional roles in forest systems.
Invertebrates : are major components of forest ecosystems, affecting virtually all forest processes and uses. Many species are recognized as important pollinators and seed dispersers that ensure plant reproduction. Even so-called pests may be instrumental in maintaining ecosystem processes critical to soil fertility, plant productivity, and forest health. Invertebrates affect forests primarily through the processes of herbivory and decomposition. They are also involved in the regulation of plant growth, survival, and reproduction; forest diversity; and nutrient cycling. Typically, invertebrate effects on ecosystem structure and function are modest compared to the more conspicuous effects of plants and fungi. However, invertebrates can have effects disproportionate to their numbers or biomass. Changes in population size also affect the ecological roles of invertebrates. For example, small populations of invertebrates that feed on plants may maintain low rates of foliage turnover and nutrient cycling, with little effect on plant growth or survival, whereas large populations can defoliate entire trees, alter forest structure, and contribute a large amount of plant material and nutrients to the forest floor. Different life stages also may represent different roles. Immature butterflies and moths are defoliators, whereas the adults often are important pollinators.
4. MICROORGANISMS: Microorganisms, including bacteria, fungi, and protists, are the most numerous and the most diverse of the life forms that make up any forest ecosystem. The structure and functioning of forests are dependent on microbial interactions. Four processes are particularly important: nitrogen fixation, decomposition and nutrient cycling, pathogenesis, and mutualistic symbiosis.
Nitrogen fixation is crucial to forest function. While atmospheric nitrogen is abundant, it is unavailable to trees or other plants unless fixed, that is, converted to ammonia (NH4), by either symbiotic or free-living soil bacteria.
Microorganisms reduces the mass of litters thereby improving the fertility of soils as the organic residue is incorporated.
Some bacteria and many fungi are plant pathogens, obtaining their nutrients from living plants. Some are opportunists, successful as saprophytes, but capable of killing weakened or wounded plant tissues. Others require a living host, often preferring the most vigorous trees in the forest. Pathogenic fungi usually specialize on roots or stems or leaves, on one species or genus of trees.
Pathogenic fungi are important parts of all natural forest ecosystems. The forest trees evolved with the fungi, and have effective means of defense and escape, reducing the frequency of infection and slowing the rates of tissue death and tree mortality. However, trees are killed, and the composition and structure of the forest is shaped in large part by pathogens.
Pathogens remove weak or poorly adapted organisms from the forest, thus maintaining the fitness of the population. Decay fungi that kill parts of trees or rot the heartwood of living trees create an essential habitat for cavity-nesting birds and the other animals dependent on hollow trees.
By killing trees, pathogens create light gaps in the forest canopy. The size and rate of light gap formation and the relative susceptibility of the tree species present on the site determine the ecological consequences of mortality. Forest succession is often advanced as shade-tolerant trees are released in small gaps. Gaps allow the growth of herbaceous plants in the island of light, creating habitat and food diversity for animals within the forest. In many forests, pathogens are the most important gap formers and the principal determinants of structure and succession in the long intervals between stand-replacing disturbances such as wildfires or hurricanes.
The fungus roots of trees, and indeed most plants, represent an intimate physical and physiological association of particular fungi and their hosts. Mycorrhizae are the products of long co-evolution between fungus and plant, resulting in mutual dependency. Mycorrhizae are particularly important to trees because they enhance the uptake of phosphorus from soils. Mycorrhiza fungi greatly extend the absorptive surface of roots through the network of external hyphae.
5. FOREST SOIL: The soil is a feature of a forest ecosystem that is affected by the changes in climate, geology, amount of rainfall and vegetation. The soil of temperate forests is more fertile because trees leaves drop to the ground every fall. This litter contributes to the layers of organic material found in forest soil. The old leaves becomes a source for bacteria and fungi. These organisms facilitate the breaking down of the leaves and other organic material.
Decomposition enriches the forest soil as it provides more nutrients to the living trees and plants in the ecosystem. However, the soil in tropical rain forest has poor quality because of the torrential rains. The constant rain erodes and dissolves soil nutrients before the trees can benefit from them.
LAWS AND PRINCIPLES GORVERNING THE FOREST ECOSYSTEM
According to the report of the United Nations Conference on Environment and Development, the following are principles on the conservation of the forest ecosystem:
1. Forest resources and forest lands should be sustainably managed to meet the social, economic, ecological, cultural and spiritual needs of present and future generations. These needs are for forest products and services such as, wood and wood products, water, food, fodder, medicine, fuel, shelter, employment, recreation, habitat for wildlife, landscape diversity, carbon sinks and reservoirs and for other forest products. Appropriate measures should be taken to protect forest against harmful effects of pollution including air-borne pollution, fires, pests and diseases in order to maintain their full multiple value.
2. Government should promote and provide opportunities for the participation of interested parties, including local communities and indigenous people, industries, labour, non-governmental organization and individuals, forest dweller, and women in the development, implementation and planning of national forest policies
3. The role of planted forest and permanent agricultural crops are sustainable and environmental sound sources of renewable energy and industrial raw materials should be recognized, enhanced and promoted. Their contributions to the maintenance of ecological processes to offsetting pressure on primary/old growth forest and to providing regional employment and development with adequate involvement of local inhabitant should be recognized and enhanced.
4. The provision of timely, reliable and accurate information on forests and forest ecosystem is essential for public understanding and informed decision-making should be ensured
5. Indiscriminate felling of trees and hunting of wild animals is prohibited in the forest
NUTRIENT CYCLING IN A FOREST ECOSYSTEM
Nutrient cycling in a forest ecosystem refers to the movement of certain nutrients like Nitrogen, Carbon, water and other elements from the forest environment into various organisms and back to the forest environment. A functioning forest ecosystem uses both energy and inorganic nutrient. As energy flow is unidirectional, it is constantly supplied by the sun from outside the ecosystem. Inorganic nutrients, however, need not to be supplied from outside as they can be recycled within the ecosystem.
Carbon, oxygen, nitrogen and water are the main nutrients which are necessary for the maintenance of life in the ecosystem. The cycling of these nutrients in nature is brought about by physical, chemical, and biological processes. The nutrient cycle are delicately balanced in nature.
The various nutrients and how they are been cycled are explained below
CARBON CYCLE
Definition: Carbon cycle involves the series of processes which contributes to the circulation of carbon in nature. The processes are:
1. Carbon dioxide is removed from the air mainly by photosynthesis during which plants use it to manufacture their food.
2. Carbon is lost in the form of carbonates of calcium and magnesium through leaching and drainage
WATER CYCLE
Definition: water cycle is defined as the continuous movement of water from the atmosphere to the earth and from the atmosphere to the earth and from the earth to atmosphere. The process of water cycling are:
1. Rainfall or precipitation
2. Evaporation from the ocean and land,
3. Transpiration from plant,
4. Breathing or respiration by plant and animal,
NITROGEN CYCLE
The diagram below explains the way in which nitrogen is circulated in the ecosystem
ENERGY TRANSFER IN A FOREST ECOSYSTEM
Different organisms exist within the forest layers. These organisms interact with each other and their surroundings. Each organism has a role or niche in sustaining the ecosystem.
Some provide food for other organisms; others provide shelter or control populations through predation:
Producers: All living organisms’ intake energy in order to survive. In a forest ecosystem, trees and other plants get their energy from sunlight. Plants produce their own food, in the form of carbohydrates. Plants are, therefore, called the primary producers, since they produce the basic foodstuffs for other organisms within food chains and food webs. Photosynthesis is the chemical reaction that allows plants to produce their own food.
Consumers: Animals cannot produce their own food. They must consume food sources for die energy they need to survive. All animals, including mammals, insects, and birds, are called consumers. Consumers rely on plants and other animals as a food source. Details of these animals in a forest ecosystem have been given earlier.
Primary consumers only eat plants and are referred to as herbivores. Secondary consumers are referred to as carnivores that feed on herbivores. Tertiary consumers are carnivores that feed on other carnivores. Omnivores eat both plant and animal matter.
Decomposers:
Leaves, needles, and old branches fall to the forest floor as trees grow. Eventually all plants and animals die. So what happens to all of this plant and animal material? Does it sit on the forest floor forever? Thankfully no. These materials are decomposed by worms, microbes, fungi, ants, and other bugs.
Decomposers break these items down into their smallest primary elements to be used again. Decomposers are important in that they sustain the nutrient cycle of ecosystems.
Humans are part of Forest Ecosystem:
Humans are consumers. We get food and materials from forests. Because of this, we are a part of the forest ecosystem. Human consumption alters forest ecosystems. Human intervention may be necessary to sustain forest communities under the increased pressure of human use.
SUMMARY OF ENERGY TRANSFER IN A FOREST ECOSYSTEM
The relations between the different components of an ecosystem are so close that, if one of them is damaged , the whole ecosystem is affected. The main relations are those established between energy flow and nutrient flow. The ecosystem is an open system as far as energy is concerned, that is energy continuously gets in and out of the system. The energy enters mainly from the sun, goes through the biotic community and its food chain, and goes out as heat, organic matter and resulting organisms. More into detail, the organism produced are able to catch and use the solar energy in order to transform some inorganic compounds into organic compounds, through the photosynthesis. These compounds are used by producers in two ways; to live and grow (the organic compounds form new structural elements of plant like leaves and new branches). Herbivores, by eating vegetables absorb their organic substances and metabolize them, i.e. transform them into other organic substances that can be used for all vital functions (breathing, movements, body temperature and many others)and use them as structural material in order to grow.
Carnivore animals behave quite similarly, eating other animals. The process goes on in this way, from one category of organisms to another one. The transfer of energy through the food chain determines some heat to be lost into the environment, according to the second thermodynamics principle. This means that carnivores will have less energy while eating, than herbivores, that in turn will receive from their food .The energy transfer percentage for a trophic level to the next one is defined as ecological efficiency or efficiency of the food chain.
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