2.5 Zonation, succession and change in ecosystemsIB Environmental Systems and Societies HL: Subtopic test

1. 1
   Glacier Bay in south-east Alaska was filled with ice until about 250 years ago. As the glacier has retreated by tens of kilometres, it has left bare gravel and clay (moraine) with no soil. Ecologists have studied the land at different distances from the glacier, which were exposed at different times. Near the ice there are mosses, lichens and mountain avens. Further away there are thickets of willow and Sitka alder. The oldest ground, furthest from the ice, is covered by forest of Sitka spruce and western hemlock.

   (a)

   Which type of succession is taking place on the moraine exposed by the retreating glacier?

   [1 mark]

   • ASecondary succession, because the area was once covered by glacier
   • BPrimary succession, because the new substratum has no soil and no earlier community
   • CZonation, because the area changes from year to year
   • DA tipping point, because the glacier melted quickly

   (b)

   What is the spruce and hemlock forest at the oldest sites called?

   [1 mark]

   • AA pioneer community
   • BA seral community that will be replaced
   • CAn environmental gradient
   • DThe climax community

   (c)

   Explain how the alder thickets make it possible for spruce to replace them.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Students laid a 300 m transect inland from the beach across the sand dunes of the Sefton Coast, Merseyside. At 10 m (young dunes with sand couch grass): soil pH 8.4, organic matter 0.3%, plant cover 10%. At 100 m (marram grass dunes): pH 8.0, organic matter 1%, plant cover 40%. At 200 m (fixed dunes with mosses and lichens): pH 7.2, organic matter 3%, plant cover 85%. At 300 m (dune scrub of sea buckthorn and creeping willow): pH 6.4, organic matter 8%, plant cover 100%.

   (a)

   What is the main reason for using a transect in this investigation?

   [1 mark]

   • ATo measure how biotic and abiotic factors change along the gradient from the beach inland
   • BTo estimate the size of a mobile population
   • CTo find the carrying capacity of the dunes
   • DTo measure net productivity of the dunes

   (b)

   Which term describes the change in the plant community from the beach to the scrub?

   [1 mark]

   • ABiomagnification
   • BCarrying capacity
   • CZonation
   • DSequestration

   (c)

   Explain why soil organic matter and plant cover increase with distance from the sea along the transect.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Ecologists studied the net and gross productivity of three plant communities that represent stages in the succession on abandoned farmland in a temperate region, in g carbon per m² per year. Year 5, herbaceous weeds and grasses: gross productivity 600, respiration 150. Year 30, young forest: gross productivity 1,800, respiration 700. Year 200, mature forest: gross productivity 2,000, respiration 1,900. The weeds in the year 5 community produce huge numbers of small seeds that are spread by wind. The oak trees in the mature forest produce relatively few large acorns that are provisioned with food reserves.

   (a)

   Calculate the net productivity and the net productivity as a percentage of gross productivity for the year 5 and year 200 communities, and describe the trend.

   [3 marks]

   (b)

   Using the information about the seeds, explain which type of reproductive strategy is found in the year 5 and the year 200 communities.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Lowland heathland in southern England, for example in Dorset and Surrey, is open land of heather, gorse and bracken on poor, acidic, sandy soils. It supports specialist wildlife such as the nightjar, Dartford warbler, sand lizard and smooth snake. It was created thousands of years ago when people cleared the original woodland and then kept the land open by grazing livestock, cutting turf and burning. Where these practices have stopped, birch and pine seedlings establish and the heath turns into woodland. Conservation bodies now cut scrub and graze heathland with ponies and cattle to keep it open.

   (a)

   Explain how the type of community that develops in a succession is influenced by factors other than time, and how human activity has produced lowland heathland.

   [6 marks]

   (b)

   Evaluate the management of lowland heathland to keep it open, compared with allowing succession to proceed to woodland.

   [6 marks]

   Total for question 4: 12 marks

End of questions