8.4
Human activity can affect local habitats In this topic, you will learn that:
• organisms constantly have an impact on the environment around them (their habitat) • people make both positive and negative changes to the environment • understanding the impacts is the first step to reducing and reversing them.
Land degradation Human activities have led to a degradation of the physical environment. Soil erosion is a major problem caused by the clearing of land for agriculture. In ecosystems with many trees, the soil is stabilised by a dense mat of plant roots. Its surface is covered by a layer of leaf litter, which protects the soil surface from erosion by wind and water. Water from rainfall is quickly absorbed through the top layers of soil. Once land is cleared of trees for agriculture, there is little to protect the soil from the action of wind and water. Grazing by animals with hard hooves, such as cattle, compacts the soil. This slows water absorption into the soil and increases the amount of water run-off. This, in turn, erodes the soil. Wind also contributes to the removal of the nutrient-rich topsoil.
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Animals use resources such as food and water and, in turn, provide resources for other organisms. Humans are certainly no exception. Human impact on environments is considerable because of our population numbers and our ability to manipulate our surroundings to suit our needs. Many environmental changes so far have been detrimental.
Deforestation
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Figure 1 Only one specimen of the Hastings River mouse has ever been found. It is considered extinct due to changes brought about by European settlement.
Our landscape was once covered by patches of different types of landscapes, such as swamp, grassland, forest and heath. This variety of vegetation supported many species of animals that moved, reproduced and spread throughout their territories and beyond. Since European settlement, over 44 per cent of Australia’s original bushland has been cleared. Much of that land is used for housing, to grow food or to manufacture products. The food webs that existed in these areas have been changed as new predators (such as dogs and cats) move in and the number of producers decreases.
Figure 2 In 1983, large amounts of topsoil were carried across Melbourne and into the Southern Ocean as a result of wind erosion.
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