Short notes on land use change and its impacts, and on the structure of an ecosystem

The question asks for any two notes; notes (i) and (iii) are answered.

(i) Land use change along with its impacts

Land use change is the conversion of land from one use or cover to another: forest to farmland, grassland to irrigated fields or factories, wetland to housing, farmland to roads and towns. Land is a basic resource needed for food, animal husbandry, industry and settlements, and these intensive uses are usually extended at the cost of the remaining forests, grasslands, wetlands and deserts. The main drivers are a growing population's need for food (a hunger for land), urban and industrial growth, and short-term economic gain. An everyday Indian example is the farmland on the edge of a growing city that is sold for housing colonies and warehouses.

Impacts

• Loss of forests and their services. The most damaging change in land use is how fast forests have vanished; with them go oxygen supply, removal of carbon dioxide, control of water flows, slowing of erosion, and products such as food, fodder, timber and medicinal plants.
• Loss of grasslands and wetlands. Natural wetlands are drained for farming, and grasslands are turned into irrigated farms or industrial areas; in India permanent pastures now cover only 3.7 per cent of the land.
• Degraded soil. Grasslands converted to sugarcane in the Deccan turned saline after continuous irrigation and became useless within a few years; overgrazed or deforested land becomes wasteland.
• Shrinking farmland. As cities and industries spread, agricultural land and forests shrink, with long-term ill effects.
• Loss of wildlife habitat. A wilderness cannot be recreated artificially, which is why a rational land-use policy has to decide how much land goes to each use and where.

(iii) The structure of an ecosystem

An ecosystem is a functional unit of nature in which living organisms interact with one another and with their physical surroundings; it may be as small as a pond or as large as a forest or a sea. Its structure is the way its non-living and living parts are arranged.

Abiotic components

These are the non-living parts: water, air and soil with their dissolved inorganic and organic substances, together with sunlight, temperature, day-length and other climatic conditions, which regulate how fast the whole system works. In a pond, for instance, the abiotic part is the water with its dissolved substances and the soil deposit at the bottom.

Biotic components

• Producers (autotrophs): green plants and algae that use the sun's energy to make organic matter; in a pond, phytoplankton and the floating, submerged and marginal plants.
• Consumers (heterotrophs): animals that feed on producers or on other animals; in a pond, zooplankton and the free-swimming and bottom-dwelling animals.
• Decomposers: fungi, bacteria and flagellates that break down dead matter and return its minerals for reuse by the producers.

The interaction of these components gives each ecosystem a characteristic physical structure, described by its species composition (the plant and animal species present) and its stratification, the vertical layering of species: in a forest, trees form the top layer, shrubs the second and herbs and grasses the lowest.