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Positive and negative impacts of people on the environment

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Presentation on theme: "Positive and negative impacts of people on the environment"— Presentation transcript:

1 Human Management & Impact in a Mid Latitude Grassland Ecosystem Case Study: Prairies USA
Positive and negative impacts of people on the environment Describe and explain how people have attempted to manage this ecosystem Key terms: monoculture, soil erosion

2 Natural causes of ecosystem destruction
1. Unpredictable rainfall and period of drought. For example in the 1930s a combination of low rainfall and bad farming practices lead to the formation of the American Dust Bowl which saw short grasses spread east. 2. Lightning causes summer fires which destroyed vegetation and small animals. 3. Bison herds were heavy grazers, they ate the coarse medium grass leaving just short grasses. Also their practice of rolling on the ground to scratch their back destroyed the vegetation.

3 Human causes of ecosystem destruction and negative impacts
1. Hunting for food, particularly bison. Use of horses and rifles increases rate of killing. 2. Trapping (fur traders) – bison and elk in the 18th & 19th century. Large mammals greatly reduced in number from many millions to now just existing in protected areas. 3. Cattle ranching in the west. Overgrazing a problem and irrigation was needed to produce fodder crops for winter, this use of water lowered the water table. 4. Cereal farming – took off after 1840s with the use of a steel plough. Overcultivation in 1930s lead to soil erosion – Dust Bowl. Worsened by droughts in 1950 & 1985. Some fields lost 1m depth of soil to the wind. 5. Intensive Cattle Production e.g. Denver – cattle fattened in stockyards on grain & silage produced on the prairie. Benefit over ranching is that animals do not lose condition by being left to roam freely. Soil in stockyard areas suffer from severe trampling.

4 Human causes & impacts continued…
6.Mineral extraction- from 1970s strip mining of coal & oil exploration (50 wells). Many roads, railways and pipelines had to be built – loss of grassland habitat and associated fauna. 7. Damming of major river to allow for flood control and irrigation schemes. Leads to areas of grassland being flooded by reservoirs, and areas downstream of dams drying up because of reduced river discharge and less risk of flooding. 8. Draining of wetland areas for crops – flora and fauna completely changed.

5 Reasons for monoculture - wheat
5. Population pressure – very low population density allows very extensive farming 6. In Canada the govt have guaranteed prices for wheat (like EU) 7. The whole infrastructure is geared to large scale wheat production e.g. railways & grain-elevators 8. Great demand in market place for cereal Richness of soil suits cultivated grasses (cereals) 2. Ease of management once established e.g. same inputs each year – seed, machinery 3. Flat landscape suits mechanised farming e.g. combine harvesters 4. Climate suits wheat – not too wet – needs sunshine & showers in last 2 mths to fatten the grain

6 Effects of monoculture
NEGATIVE Soil exhaustion can be a problem – nitrogen constantly removed by wheat 2. This means agro-chemicals are used and can go into water system 3. Loss of hedge rows and habitats which can remove potential pests 4. Very monotonous landscapes 5. Danger of concentrating on one crop which can lead to disease killing the crop 6. Decrease in soil value and structure in the long term 7. Emergence of herbicide resistant weeds POSITIVE 8. Guaranteed high yields every year 9. Very important economically to Canada – number 1 exporter worldwide

7 Protective measures: US govt established 1,539,478 ha of National Grasslands to be managed by the Forest Service. 18 National Grasslands set up. Forest Service have to work with lease holders and private landowners to protect against overgrazing & over cultivation e.g. limit the numbers of cattle at different times of year to protect vegetation cover. 60 years ago a large govt. range research centre was established £200,000 per yr from oil industry in the area goes to Forest Service. Provision of camp grounds, picnic sites & facilities for bird watching.

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