An ecosystem is a community of interdependent plants, animals and microbes living in and interacting with their particular environment. The biotic components are all the living things in the system. The abiotic components are the non-living things: physical and chemical factors such as light, weather and the gases and minerals in the air and soil. The relationships that link the abiotic and biotic components are based on two main processes: the flow of energy and the cycling of material elements through the system. The forest ecosystem is dominated by trees, the things they need to survive, and the resources they provide to the rest of the forest community.
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The biotic components of the forest ecosystem are trees, shrubs, herbs and grasses; the herbivores that feed directly on these plants; the carnivores that feed on the herbivores; and the saprophytes or detritovores that live on decaying animal or vegetable matter. Herbivores range from leaf-eating caterpillars to berry-eating birds and grazing mammals like rabbits or deer. Carnivores include insect-eating bats, spiders, dragonflies and birds as well as larger predators like badgers and foxes. Saprophytes include the fungi that are the main decomposers of timber; earthworms that eat fallen leaves; millipedes, maggots and microscopic algae and bacteria.
The three main types of abiotic components are climatic factors such as temperature, light and rainfall; edaphic (soil-related) factors such as the proportions of sand, rock or clay in the soil; and the availability of material elements such as carbon, nitrogen, sulphur, potassium and other minerals. Abiotic factors directly affect what grows where. For example, the sunlight needed for photosynthesis is abundant at leaf-canopy level, while only shade-tolerant species grow at ground level. Rainfall pooling in the boles and ridges of tree trunks supports insect life, mosses and fungi. Wind disperses seeds and helps pollination. Cold climates favour narrow-leaved conifers whose needles resist drying and freezing[ref 3]. The structure of the soil determines how easily water flows through it to feed the vegetation. Elements such as carbon, nitrogen and minerals are essential nutrients, which are captured by plants from the soil or air and passed through the food web to other living things.
Energy transformation process
During photosynthesis, green leaves transform the radiation energy in sunlight into chemical energy, which turns carbon dioxide and water into the carbohydrates that make up their structure and the oxygen that all living things need to fuel their growth. The abiotic components of chemical materials and physical forces in the forest ecosystem thus give rise to its primary biotic components – the plants on which herbivores and detritovores feed – and sustain the flow of energy through the system in the form of food chains.
Biogeochemistry describes how biotic components both influence and are controlled by the abiotic geology and chemistry of the earth in a never-ending cycle. Carbon, nitrogen, phosphorus and iron are present in certain ratios in algae at the bottom of the food chain and thus in all levels (trophes) of consumers further up the chain. Detritivores break down the complex body chemistry of dead plants and animals into simpler elements that can be re-used as nutrients. For example, the compost that feeds tree roots comes from the action of earthworms, fungi and bacteria in consuming and breaking down fallen leaves and rotting timber. Through a process of symbiosis, fungal mycorrhizae take sugars from the tree roots they colonise but also feed the roots with other nutrients absorbed from the soil.
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