Question 1
Distinguish between zonation and succession.
[2]
Question 2
Two sites begin succession at the same time. Site X is newly exposed volcanic rock. Site Y is an abandoned field with its soil still present.
Identify the type of succession occurring at each site.
[1]
Explain why succession is likely to proceed more rapidly at site Y.
[2]
Question 3
Students investigate plant zonation from the edge of a pond to dry ground, as shown in the fieldwork diagram.
Outline four features of a suitable method for investigating the zonation.
[4]
Question 4
The graph shows the percentage cover of three plant species along a transect from wet ground to dry ground. Soil moisture was measured at the same positions.
Identify the species most strongly associated with the driest part of the transect.
[1]
Describe the relationship between soil moisture and the distribution of species A.
[2]
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Question 5
Compare the reproductive strategies and successional associations of -strategists and -strategists.
[4]
Question 6
Students used a belt transect to investigate vegetation along a gradient from the edge of a marsh to dry ground. Table 1 shows plant cover and soil moisture along the transect.
Vegetation cover and soil moisture along a 50 m belt transect from the marsh edge to dry ground.
| Distance / m | Marsh sedge cover / % | Creeping herb cover / % | Tussock grass cover / % | Dwarf shrub cover / % | Soil moisture / % |
|---|---|---|---|---|---|
| 0 | 70 | 10 | 0 | 0 | 78 |
| 10 | 60 | 30 | 10 | 0 | 70 |
| 20 | 0 | 65 | 25 | 0 | 59 |
| 30 | 0 | 35 | 60 | 15 | 45 |
| 40 | 0 | 10 | 60 | 45 | 34 |
| 50 | 0 | 0 | 20 | 75 | 26 |
Identify the plant species with the greatest cover at 50 m.
[1]
Calculate the percentage decrease in soil moisture between 0 m and 50 m. Show your working.
[2]
Describe the distribution of creeping herb and tussock grass along the transect.
[2]
Suggest why the data do not demonstrate that soil moisture alone causes the observed plant zonation.
[2]
Question 7
A geographic information system (GIS) was used to classify vegetation on the abandoned 100-hectare Marula Farm. Figure 2 shows the same area at three dates. Cultivation stopped in 1990, but the previously developed soil remained.
State the dominant vegetation class in 2005.
[1]
Calculate the increase in woodland area between 2005 and 2025.
[1]
Describe two changes in vegetation shown between 1990 and 2025.
[2]
Explain how the changes shown provide evidence of secondary succession.
[3]
Question 8
Lichens and mosses colonize exposed rock at the beginning of a succession.
Explain how these pioneer organisms can facilitate the establishment of later seral communities.
[4]
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Question 9
During an intermediate stage of succession, gross productivity is and community cellular respiration is .
Calculate net productivity. Show your working.
[1]
Explain why net productivity usually approaches zero in a climax community.
[2]
Question 10
A temperate grassland is grazed by livestock each year. Shrub and tree seedlings are eaten, so the grassland remains open. When grazing is excluded, tall herbs and shrubs begin to establish.
Define the term plagioclimax.
[1]
Explain why the grazed grassland is a plagioclimax.
[3]
Question 11
Students investigated zonation on a sheltered rocky shore. They placed five belt transects perpendicular to the shoreline and sampled percentage cover in quadrats at fixed heights above the low-water mark.
Identify the organism with the greatest mean percentage cover at 1.5 m above the low-water mark.
[1]
Calculate the percentage decrease in bladder wrack cover between 0.5 m and 2.0 m above the low-water mark. Show your working.
[3]
Describe the zonation of barnacles and orange lichens shown in Figure 1(a).
[3]
Explain how one abiotic gradient shown in Figure 1(b) may contribute to the distribution of bladder wrack.
[3]
Evaluate whether this investigation demonstrates that air-exposure time is the main cause of the observed zonation.
[4]
Question 12
Ecologists compared succession on fresh volcanic ash at site V and on soil remaining after a severe fire at site F. Figure 3 shows changes during the first 40 years.
Changes during the first 40 years of succession at site V (fresh volcanic ash) and site F (soil remaining after severe fire).
| Time / years | : vegetation cover / % | : vegetation cover / % | : soil depth / cm | : soil depth / cm | : plant species richness | : plant species richness |
|---|---|---|---|---|---|---|
| 0 | 0 | 5 | 0.0 | 14.0 | 0 | 3 |
| 10 | 12 | 58 | 0.6 | 15.0 | 4 | 18 |
| 20 | 38 | 82 | 1.8 | 16.0 | 11 | 31 |
| 40 | 72 | 94 | 4.0 | 18.0 | 23 | 39 |
Identify the site undergoing primary succession.
[1]
Calculate the mean rate of increase in soil depth at site V over the 40 years.
[2]
Explain why vegetation cover and plant species richness increased more rapidly at site F than at site V.
[3]
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Question 13
Two grassland plots were exposed to the same 30-day drought. Plot E was an early-seral community and plot L was a late-seral community. The table shows species richness before the drought and net primary productivity relative to pre-drought values before, during and after the drought.
Determine the difference in species richness between plots E and L before the drought.
[1]
Compare the changes in net primary productivity of the two plots during and after the drought.
[3]
Explain how the data support a link between succession, diversity and resilience.
[3]
Question 14
Researchers recorded reproductive traits and abundance of four plant species during succession on abandoned quarry spoil. The table presents their results.
Identify the species most characteristic of the pioneer stage.
[1]
State two pieces of evidence that species D shows a -strategist tendency.
[2]
Describe the change in dominance of the plant community over the 140 years.
[2]
Explain why the reproductive strategy of species A is better suited to pioneer conditions than that of species D.
[2]
Question 15
Explain how succession may increase the resilience of an ecosystem to disturbance.
[4]
Question 16
The cross-section shows different late-successional communities within one climatic region.
Explain how two physical factors shown may cause different final communities to develop.
[4]
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Question 17
Two sites experience similar climate and have similar soils. One remains as closed woodland, while the other persists as open wood-pasture with abundant large herbivores.
Define an alternative stable state.
[1]
Explain how this observation challenges the traditional concept of a single climax community.
[3]
Question 18
A peat core was collected from Lake Noru, a temperate upland basin. Deeper peat layers are older. Researchers identified pollen preserved at five depths and used radiocarbon dating to estimate the age of each layer.
State the dominant pollen type in the oldest sampled layer.
[1]
Calculate the mean rate of peat accumulation between 6100 and 2600 years before present. Give your answer in millimetres per year. Show your working.
[3]
Describe the changes in vegetation indicated by the pollen record from the oldest sampled layer (6100 years before present) to the youngest sampled layer (300 years before present).
[3]
Explain how the pollen record provides evidence of succession.
[3]
Assess the reliability of the conclusion that the basin underwent a single, continuous succession from grassland to woodland.
[4]
Question 19
Retreat of the Kaldur Glacier has exposed a sequence of mineral surfaces. Ecologists used the known position of the glacier front in different years to compare sites exposed for different lengths of time.
Mean ecosystem development measurements at sites exposed after glacier retreat.
| Years since exposure / years | Vegetation cover / | Soil depth / cm | Species richness / species per plot | Soil organic matter / |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 5 | 4 | 0.3 | 3 | 0.2 |
| 20 | 19 | 1.8 | 9 | 1.1 |
| 55 | 53 | 5.6 | 18 | 3.7 |
| 110 | 81 | 11.2 | 27 | 7.9 |
| 180 | 92 | 17.5 | 31 | 11.8 |
Identify the type of succession represented by the glacier foreland.
[1]
Calculate the mean rate of increase in soil depth between 20 and 110 years after exposure. Show your working.
[3]
Describe two relationships shown in Figure 3(b).
[2]
Explain how the observed changes in soil may allow later seral communities to replace pioneer communities.
[4]
Evaluate the use of this chronosequence as evidence for changes through primary succession at the glacier foreland.
[5]
Question 20
Figure 5 shows gross productivity and community respiration during succession on a newly formed coastal dune. Productivity is measured in .
Calculate net productivity during the developing stage at 25 years. Show your working.
[2]
Determine net productivity in the climax stage.
[1]
Describe the relationship between biomass and net productivity during succession.
[2]
Explain why net productivity approaches zero in the climax stage even though gross productivity remains high.
[2]
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Question 21
Figure 6 shows four late-successional communities within the same climatic region. The sites have experienced no direct land clearance for 80 years.
Identify the site with the deepest soil.
[1]
Explain why woodland has developed at site Q but not at site P.
[2]
Explain how drainage influences the contrasting communities at sites Q and R.
[2]
Analyse how Figure 6 challenges the idea that one regional climate must produce one climax community.
[2]
Question 22
Outline how an environmental gradient may produce zonation in an ecosystem.
[4]
Explain the strengths and limitations of using transect evidence to determine the variables affecting species distribution.
[7]
Using named examples, evaluate the usefulness of understanding zonation when managing ecosystems.
[9]
Question 23
Top predators are removed from a woodland ecosystem. The population of browsing herbivores subsequently increases.
Explain how this top-down change may alter the final community produced by succession.
[4]
Question 24
A severe cyclone removed most vegetation from parts of the Ranu Estuary, but sediment and buried roots remained. Two damaged areas were monitored: area N was allowed to recover naturally, while native mangrove seedlings were planted in area P. An undamaged mature mangrove area, M, was also monitored.
The shoreline sediment-loss values are net measurements relative to the year-0 shoreline; a decrease indicates subsequent sediment deposition.
Recovery indicators in mangrove areas during eight years after cyclone damage; net shoreline loss is relative to the year-0 shoreline, so a decrease indicates sediment deposition.
| Indicator | Area | Year 0 | Year 1 | Year 3 | Year 5 | Year 8 |
|---|---|---|---|---|---|---|
| Vegetation cover / % | 6 | 13 | 29 | 47 | 66 | |
| Vegetation cover / % | 7 | 28 | 55 | 76 | 88 | |
| Vegetation cover / % | 94 | 91 | 93 | 95 | 94 | |
| Plant species richness / species | 4 | 6 | 10 | 14 | 17 | |
| Plant species richness / species | 4 | 8 | 13 | 18 | 21 | |
| Plant species richness / species | 25 | 24 | 25 | 26 | 25 | |
| Net shoreline loss relative to year 0 / cm | 0 | 18 | 31 | 38 | 41 | |
| Net shoreline loss relative to year 0 / cm | 0 | 12 | 18 | 19 | 17 | |
| Net shoreline loss relative to year 0 / cm | 0 | 3 | 5 | 4 | 4 |
Identify the type of succession occurring in areas N and P.
[1]
Calculate the ratio of the increase in vegetation cover in area P to the increase in area N between years 0 and 5. Show your working.
[3]
Compare the recovery of areas N and P during the eight years after the cyclone.
[3]
Explain how increasing plant species richness and vegetation cover may increase the resilience of the recovering mangrove ecosystem.
[4]
Evaluate the conclusion that planting seedlings restored area P to a stable equilibrium within eight years.
[4]
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Question 25
Ecologists studied succession on a newly deposited river bar. Sites of known age were used to estimate changes in productivity, biomass and the reproductive traits of dominant plants.
Reproductive traits of the dominant plant at sites of different ages.
| Site age / years | Dominant plant | Seeds per adult (annual output) | Mean seed mass (per seed) / mg | First reproduction (age) / years | Bare-ground colonization (success) / % |
|---|---|---|---|---|---|
| 2 | Annual herb | 18 000 | 0.3 | 1 | 72 |
| 12 | Perennial grass | 4200 | 0.8 | 2 | 46 |
| 35 | Thorny shrub | 680 | 12 | 4 | 21 |
| 80 | Fast-growing tree | 190 | 95 | 8 | 8 |
| 160 | Shade-tolerant tree | 34 | 620 | 18 | 2 |
Calculate net productivity at the 35-year site. Show your working and give the correct unit.
[3]
Determine the net productivity at the 160-year site and compare it with that at the 12-year site.
[3]
Analyse the relationship between standing biomass and productivity during the succession.
[4]
Explain how the reproductive data support a change from predominantly -strategist tendencies to predominantly -strategist tendencies.
[3]
Analyse whether the productivity and reproductive data support classifying the 160-year site as a climax community.
[3]
Question 26
Succession was studied on four abandoned serpentine-mining terraces in the same valley. Mining ended 95 years ago, and no terrace has since been cultivated. All terraces experience the same regional climate.
Soil and vegetation measurements from four abandoned mining terraces in the same valley.
| Terrace | Soil depth / cm | Soil pH | Soil moisture / % | Available N / g | Woody cover / % | Species richness / plot |
|---|---|---|---|---|---|---|
| A | 9 | 8.1 | 14 | 0.4 | 6 | 18 |
| B | 64 | 6.4 | 31 | 3.8 | 74 | 31 |
| C | 47 | 5.8 | 78 | 2.1 | 3 | 14 |
| D | 21 | 6.7 | 19 | 1.2 | 22 | 26 |
Identify the terrace with the greatest woody vegetation cover.
[1]
Compare the soil conditions of terraces B and C.
[3]
Explain why mixed woodland has developed on terrace B but not on terrace A.
[4]
Analyse how waterlogging and fire may have influenced the communities on terraces C and D.
[4]
Evaluate the claim that regional climate is the main factor determining the late-successional community on these terraces.
[4]
Question 27
An upland conservation area contains two similar 20-hectare plots. Domestic grazers were removed from plot U in year 0 but continued to graze plot G. Figure 8 shows vegetation change and the management history.
Calculate the percentage increase in woody vegetation cover in plot U between year 0 and year 25.
[2]
Explain why plot G may be described as a plagioclimax.
[2]
Explain how the results support the existence of alternative stable states.
[2]
Evaluate the conclusion that woodland is the single inevitable climax community for this upland.
[2]
Question 28
Explain the development of seral communities during primary succession.
[4]
Explain changes in ecosystem structure and functioning that may occur as succession proceeds.
[7]
Using named examples, examine the claim that facilitation is the main process controlling primary succession.
[9]
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Question 29
Outline the meanings of resilience, stability and equilibrium in ecosystems.
[3]
Explain how succession may alter the capacity of an ecosystem to tolerate disturbance and maintain equilibrium.
[8]
Using named examples, discuss whether allowing secondary succession is the most effective strategy for restoring disturbed ecosystems.
[9]
Question 30
In the Vardena Reserve, a native predator was reintroduced in year 0 after being absent for several decades. Researchers monitored two similar sectors. Predator access was allowed in sector R, while predator-proof fencing excluded the predator from sector E. Wild browsing herbivores remained in both sectors.
Figure 7(a). Measurements in sectors R (predator access) and E (predator excluded); predator reintroduction occurred in year 0.
| Year | Herbivore density, R / animals km | Herbivore density, E / animals km | Browsing damage, R / % | Browsing damage, E / % | Woody cover, R / % | Woody cover, E / % |
|---|---|---|---|---|---|---|
| 0 | 24 | 23 | 71 | 69 | 18 | 19 |
| 2 | 20 | 25 | 62 | 73 | 19 | 18 |
| 5 | 14 | 27 | 46 | 78 | 23 | 17 |
| 10 | 10 | 29 | 28 | 82 | 34 | 16 |
| 15 | 9 | 28 | 24 | 80 | 47 | 15 |
| 20 | 8 | 30 | 21 | 84 | 61 | 14 |
Calculate the percentage decrease in herbivore density in sector R from year 0 to year 20. Show your working.
[3]
Compare the vegetation changes in sectors R and E.
[3]
Explain how predator reintroduction may have produced the vegetation change in sector R through top-down control.
[4]
Analyse how the results support the concept of alternative stable states.
[3]
Evaluate the conclusion that, without human influence, closed woodland is the inevitable climax community of the reserve.
[3]
Question 31
Coastal heath at Cape Luma has been managed for generations by rotational cutting. Managers established four treatments to investigate whether intervention diverts succession: annual cutting, cutting every five years, cutting stopped in year 0, and an unmanaged woodland reference site.
Vegetation measurements at Cape Luma heath plots over 16 years. Five-year cutting events occurred in years 0, 5, 10 and 15.
| Treatment | Year | Shrub cover / % | Tree seedlings / | Heath specialists / species per plot |
|---|---|---|---|---|
| Annual cutting | 0 | 42 | 3 | 14 |
| Annual cutting | 4 | 39 | 2 | 15 |
| Annual cutting | 8 | 40 | 2 | 14 |
| Annual cutting | 12 | 38 | 1 | 15 |
| Annual cutting | 16 | 41 | 2 | 14 |
| Five-year cutting (events: 0, 5, 10, 15) | 0 | 44 | 4 | 13 |
| Five-year cutting (events: 0, 5, 10, 15) | 4 | 52 | 9 | 15 |
| Five-year cutting (events: 0, 5, 10, 15) | 8 | 47 | 5 | 14 |
| Five-year cutting (events: 0, 5, 10, 15) | 12 | 55 | 13 | 16 |
| Five-year cutting (events: 0, 5, 10, 15) | 16 | 49 | 7 | 15 |
| Cutting stopped in year 0 | 0 | 43 | 4 | 14 |
| Cutting stopped in year 0 | 4 | 58 | 18 | 12 |
| Cutting stopped in year 0 | 8 | 70 | 39 | 9 |
| Cutting stopped in year 0 | 12 | 78 | 62 | 7 |
| Cutting stopped in year 0 | 16 | 82 | 86 | 5 |
| Woodland reference | 0 | 18 | 112 | 3 |
| Woodland reference | 4 | 17 | 118 | 3 |
| Woodland reference | 8 | 19 | 121 | 2 |
| Woodland reference | 12 | 18 | 125 | 3 |
| Woodland reference | 16 | 20 | 129 | 2 |
Calculate the percentage increase in tree-seedling density in the treatment where cutting stopped between years 0 and 16. Show your working.
[3]
Describe the effect of cutting frequency on vegetation change.
[3]
Explain why the annually cut heath may be described as a plagioclimax.
[3]
Analyse the ecological trade-off between allowing succession and maintaining the managed heath.
[3]
Evaluate whether five-year cutting is the most sustainable management strategy for Cape Luma.
[4]
Question 32
Outline four factors that may influence the type of late-successional community developing at a site.
[4]
Explain how feedback mechanisms may maintain alternative stable vegetation states under similar climatic conditions.
[7]
Using named examples, to what extent is the concept of a single climax community useful for understanding succession?
[9]
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Question 33
Explain changes in gross productivity, community respiration and net productivity from pioneer to climax stages.
[4]
Analyse how contrasting reproductive strategies influence changes in species dominance during succession.
[7]
Using named examples, evaluate the extent to which productivity patterns and reproductive strategies can be used to predict the course of succession.
[9]
Question 34
Explain how repeated human intervention may produce a plagioclimax.
[3]
Analyse direct and indirect ways in which human activity can maintain open vegetation that might otherwise develop into woodland.
[8]
Using named examples, discuss whether maintaining plagioclimax communities is an environmentally sustainable conservation strategy.
[9]
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