Effects of human activities on habitats and their ecosystems

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Slide 1

In this presentation, we’re going to talk about the effects of various human activities on habitats and their ecosystems.
 
Slide 2

There are many different ways in which humans can affect the habitats of plants and animals. These include the destruction of habitat, particularly through land clearance, lash and burn agriculture, the use of pesticides and herbicides, land and water degradation, activities that promote erosion, acidification of the soil, increases in soil and water salinity, pollution of the atmosphere and the intentional or unintentional introduction of species.
 
Slide 3

Australia is clearing far too much of its landscape. About 90% of native vegetation along the east coast has been removed for farming, industry, mining, transport and housing. This includes about 50% of our rainforests.

(click) The impacts of land clearance can be devastating for our native species. Land clearance kills about 5 million of our land birds each year. For every 100 hectares of bushland that is cleared, somewhere between one and two thousand birds die from exposure, starvation or stress. Other species are displaced, or under threat because they have lost much of their available habitat and food sources.

(click) Native plants and animals can be killed during the clearing process, or as a result of it. Almost one half of all Australian mammal species are either extinct or endangered because of land clearing and habitat destruction.
 
Slide 4

Slash and burn agriculture is a technique that has been used for thousands of years to prepare land for farming. It is most often used in places where there is little available open land for farming because the vegetation is too dense. This particularly occurs in grasslands and rainforests in areas such as central Africa, northern South America and South East Asia.

(click) Unfortunately, slash and burn agriculture causes a number of problems for the environment. Forest cover can be lost when large areas of land are cleared, and not enough time elapses between successive slashings and burnings for the vegetation to recover. When fields are slashed, burned and farmed in close proximity to each other and in rapid succession, the plant roots that hold the soil together are lost. The water stored in the area dries up, and the soil erodes away. At the same time as the water is lost, soil nutrients can also leave the area. The soil loses the fertility it once had, and the land may turn into a desert. Finally, clearing land causes a loss of biodiversity as various plants and animals for which the area was a habitat are lost. The result can be extinction or endangerment of these species. In order to prevent these problems, slash and burn agriculture must be used in a very controlled manor. The amount of land that is turned into fields must be minimised, and it must be allowed to rest for extended periods so that the native vegetation can regrow before the next round of slashing and burning.
 
Slide 5

Sometimes animals are introduced unintentionally to an ecosystem. Introduced pest animals like wild pigs and rats not only have a negative effect on crops and farm animals, but also have a number of negative environmental impacts. These include preying on native fauna, destroying their habitats, competing for food and shelter, spreading disease and poisoning native animals by excreting toxins. We will talk about this in more detail when we talk about introduced species.

(click) To deal with introduced and other pests, both plants and animals, farmers and gardeners often spray or apply pesticides and herbicides. Unfortunately, these can be toxic to organisms other than the target organisms. This can include the humans who apply them!

(click) Over 98% of these chemicals reach destinations other than their targets because they are sprayed across wide areas. Rain water runoff can carry pesticides into lakes and rivers where it is toxic to aquatic life, while wind can carry them to other fields and pastures, towns and bushland areas. They can contaminate the soil, water and other vegetation, and kill native animals.
 
Slide 6

Human actions can affect the ability of our land and water to perform their intended functions in our environment. Some human actions that cause land degradation include deforestation, overgrazing, mismanaging farm land, irrigation, overharvesting of vegetation and industrial activities. Some causes of water quality degradation include the use of pesticides, diversion and damming of waterways, and mining and other industrial processes that pollute our waterways.

(click) The degradation of our land and water can result in increased salinity of our soil and waterways, increased soil erosion due to rain and wind, a reduction in the fertility of soil, acidification of the soil, the spread of weeds, the loss of biodiversity and habitats for our native wildlife and the pollution of our waterways.

Slide 7

Soil erosion can permanently change the characteristics of soil. Eroded soil can contain reduced nutrients, and lose its fertility. Some causes of soil erosion are overgrazing, overcropping and deforestation. Overgrazing occurs when too many animals such as sheep, cattle or goats are allowed to graze on land. These animals strip the land of vegetation and compact dry soil with their hooves. This prevents further vegetation such as grass from growing, and slow down the absorption of water by the soil. More soil is then exposed and is likely to be removed by rain and wind.

Overcropping occurs when the land is continuously cultivated, without being allowed to rest between crops. This reduces the nutrients in the soil, and so the soil becomes drier and less fertile. This means that the soil is more prone to rain and wind erosion. Overcropping usually occurs in countries or regions where there are high populations or demands for crops at market. The use of artificial fertilizers only increases the problem as it allows crops to be planted at even smaller intervals, boosting production temporarily, but further stripping the soil of nutrients.

Deforestation also leads to soil erosion. It is the chopping down of large areas of the bush and/or forests, and leaves these areas open to attack by the wind and rain, if it is not countered by responsible reforestation programmes. It quickly accelerates the natural erosion of the soil by removing the nutrients and minerals from the soil, and leaving large areas exposed to heavy rainfall and wind erosion. The loss of roots of trees makes the soil looser and easier to erode.

(click) Apart from a reduction in the amount of soil that is available for growing crops and native plants, soil erosion has harmful effects on the environment. First, it removes the fertile topsoil. The remaining soil has fewer nutrients and is less capable of holding moisture, so this leads to a reduction in the fertility of the soil. Second, as soil is blown or washed away, silt and harmful chemicals are deposited in water courses. This can divert the courses of streams, or cause flooding, leading to changes in and loss of habitats, and devastating effects for aquatic organisms. Finally, the eroded soil is blown up into the air, increasing the particulates and causing dust storms, so soil erosion causes air pollution.

 
Slide 8

Soil acidification can increase over time because of human actions. The soil becomes more acidic over time, and less hospitable to plant growth.
(click) Soil acidification affects the availability of soil nutrients to plants, making the soil less fertile. It can also increase the concentration in the soil of some minerals such as aluminium which are toxic to plants.
(click) Some human actions that increase the acidity of the soil include the use of ammonium-based nitrogen fertilisers, and the harvesting of plant materials rather than allowing them to rot. Rotting plant materials are alkaline, and their return to the soil balances the soil’s pH (or reduces its acid levels).

Slide 9

Salination refers to the build up of salt in the soil or water. This makes it less able to support life.
(click) Soil and our waterways naturally contain some salts. Natural processes such as mineral weathering or the gradual withdrawing of an ocean can increase the salt content, but human actions are also responsible for increasing the salt concentration in both soil and water.
(click) Some human causes of salination of the soil and water include irrigation using water that contains salt, pollution of waterways and erosion of the soil.

Slide 10

Increased salination can have devastating consequences for habitats. It can lead to yellowing of leaves, plant stunting and death. This can result in the loss of biodiversity for the area as saline-tolerant species take over. High soil saline content makes it more difficult for plants to draw water from the soil. Toxic ions released by mineral salts such as magnesium and potassium chlorides cause plant disease. Native plants are among those affected by high soil and water salinity. This leads to a decline in native vegetation and a loss of habitat for native species. As the plant diversity decreases, bird species lose their nesting places and the natural food sources for native wildlife diminish. Because of lower vegetation levels, soil is more likely to erode. Wetland habitats also suffer from increased salinity, with increased soil salinity leading to a loss of plant biodiversity and reduction in the amount of wetland habitat that survives. Increased water salinity has similar effects on aquatic organisms. Species which cannot tolerate the increased salt levels decline and salt-tolerant species dominate, leading to a loss of plant and animal biodiversity among the organisms that rely on the watercourse for their survival.