Presentation on theme: "Human interaction with ecosystems and its impacts Case study: A study of the impact of human activity and attempts to manage an area of mid-latitude grassland,"— Presentation transcript:
Human interaction with ecosystems and its impacts Case study: A study of the impact of human activity and attempts to manage an area of mid-latitude grassland, e.g. Prairies of USA Key points to be covered: -Characteristics of mollisols / chernozems -Soil erosion -Vegetation and monoculture in mid-lat. grasslands
Location Dry continental interiors Approx. lat. 40-60 N Russian steppes -Drier in E with distance from sea Prairies USA - 2700km from N to S - 1600km from W to E - Drier in W in rainshadow of Rockies - ppt 500mm per yr threat of drought ( 1988 drought) Eastern coasts Approx. lat. 30-40 S Pampas, S.America Downs, Australia Canterbury Plains, New Zealand
Climate - Prairies Large annual temp.range No moderating influence of the sea Summer 20 C Winter less the 0 C for a few months Clear skies so large diurnal (daily) temp. range 75% ppt falls in summer (growing season) Thunderstorms and hailstorms in summer can damage crops Oct-April can be snow covered In winter get cold blasts of arctic air but also warmer spells due to chinook wind
Vegetation in Mid-latitude Grassland Found S of coniferous forest belt NPP 600g/m2/yr (trop.grass.900g/trop.rainfor.2200g) Growth in mid-lat is less rapid Native Americans used this ecosystem but did little to alter it. Ecosystem remained in its original state until the late 19 th century. Original climatic climax has been altered by fire & human activity Today grama and buffalo grass are the dominants
Grasses FeatheredTufted Grasses up to 50cm up to 2m even coverage compact clumps Tightly knit sod (restricts tree growth & makes early ploughing difficult) Deep roots – up to 2m (reach water table, bind soil, reduce erosion) Most organic matter in grass roots (roots & rhizomes acct. for >80% of biomass)
Seasons Autumn - grasses die down - form a turf mat -seeds lie dormant until spring Winter - dormant, no growth, often snow covered Spring - seeds germinate - growth begins Early Summer - growth rapid - narrow inward curving blades of grass to limit transpiration Summer - decay of grasses - rapid accululation of humus in soil – this makes this an ideal area for cereal crops or in drier areas cattle ranching End of Summer - parched
Trees & animals Herbaceous plants & trees (willow) are found along water courses Trees are sometimes planted as windbreaks to protect crops Animals living in the grasslands: Burrowing animals (rabbits & gophers) Large herbivores (antelopes & bison) Carnivores (wolves & coyotes) Predatory birds (hawks & eagles) In 17 th century there were 60-70 mill bison, 50 mill antelopes and many grizzly bears, wolves & prairie dogs. Now few larger mammals exist except in National Parks.