Ecosystems can fight back
A. Conventional wisdom is often a poor guide. For one thing it suggests that human damage to the world’s species, habitats and ecosystems is terminal: that when things are lost, they are lost for ever. But oil spills of the sort that now threaten the Timor Sea, forest fires like those that recently afflicted Greece, and other man-made and man-assisted threats to wildlife are transient. Except in those cases in which a species is driven to extinction, the Earth’s ability to shrug such things off is often underestimated.
B. Alan Weisman shows this in his book, “The World Without Us”, which illustrates nature’s great capacity to recover. Have mankind abducted by aliens or wiped out by some Homo sapiens-specific virus, and nature, Mr Weisman reckons, would reclaim its territory with surprising speed, as weeds colonised pavements, rivers flooded subway tunnels and buildings burst as they were played like concertinas by a cycle of freezing and thawing. By Mr Weisman’s reckoning, residential neighbourhoods would return to forest in 500 years and only the most stubborn of human inventions, such as certain plastics, would prove permanent.
C. Mr Weisman’s conclusion was backed up earlier this year by a study published in the Public Library of Science by Holly Jones and Oswald Schmitz, of Yale’s School of Forestry and Environmental Studies. They used Web of Science, an online journal archive, to gather a set of 240 peer-reviewed scientific papers that measured recovery rates in large terrestrial and aquatic ecosystems. The data thus available included work on agriculture, deforestation, the introduction of invasive species, logging, mining, oil spills, overfishing and the damage done to seabeds by trawling, as well as, for comparison, naturally occurring disasters such as hurricanes.
D. The pair measured 94 aspects of how ecosystems are put together, including the ways in which nutrients cycle within them, the rates at which decomposition takes place and the sizes of their plant and animal populations, so that they could classify whether, and how fast, an area had recovered. They found that 83 of the 240 papers demonstrated complete recovery, while 90 showed a mixed response. Only 67 showed no recovery at all and, as the authors explain, more would have recovered if the projects had continued for long enough to track the changes in ecosystems that respond more slowly, such as forests.
E. Ecosystems exposed to more than one pressure, such as a forest that is first felled and then used for agriculture, took the longest to recover. Even in those cases, though, the average recovery time was, at 56 years, within a human lifetime. Sites that experienced single threats typically recovered in less than 20 years. The researchers found that recovery rates are influenced more by the type of ecosystem than by the magnitude of the damage inflicted upon it. Forests, for example, take longer to renew (42 years) than ocean floors (typically less than ten) regardless of the scale of the stresses inflicted on them.
F. Some commentators are sceptical about such positive findings. They point out that, of necessity, the study’s retrospective methodology includes papers published before researchers were required to declare any competing interests. This may have allowed, for example, an oil company to produce a report that plays down the damage done by a spillage. But such biased individual reports would be unlikely to affect the overall findings of a large study like this one.
G. Critics also question whether total ecological recovery really has been achieved as often as Ms Jones and Dr Schmitz suggest, and point to examples where it manifestly has not, such as the cod fishery of the Grand Banks, off the coast of Newfoundland, which collapsed in 1992. Almost two decades on, the cod show no sign of recovery, perhaps because new predators, such as dogfish, now dominate the waters.
H. It is true, though, that the question of what is pristine or natural can be debatable. A good example of this, which Mr Weisman uses in his book, is Dartmoor, a national park in the south-west of England. Dartmoor is considered by many to be one of Britain’s great nature wildernesses. In fact, it is a human construction, formed by tens of thousands of years’ worth of alterations such as burning and agriculture. But it is in its current state, rather than as the forest it once was, that people wish to preserve it. Ms Jones and Dr Schmitz point out that most conservation work is not actually concerned with returning landscapes to their natural or prehuman states and “instead use contemporaneous reference systems as targets”.
I. Despite their study’s limitations, and the difficulty of measuring recovery and choosing targets, Ms Jones’s and Dr Schmitz’s findings are good news for conservationists. But the final word of advice belongs to Mr Weisman as he invites people to ponder an alternative to his post-human future: “Since we’re imagining, why not dream of a way for nature to prosper that doesn’t depend on our demise?”
1. Approximate recovery time for ecosystems which experience no more than one pressure is .
2. Some critics claim the positive results may be influenced by some companies understating the they have caused .
3. The cod fishery of the Grand Banks is an example of where there has not been a complete .
4. Dartmoor was originally a .
Ms Jones and Dr Schmitz believe that people are more interested in preserving or returning 5. to a present-day condition rather than to their original
6. . However, despite the problems with
7. and recovery measurement, this latest study is a source of optimism for
8. .
AI explanationShows the answer. Tap to open.
Question Focus: Finding a specific recovery time for ecosystems with only one pressure
Correct Answer: 20 years
Why this is correct: The note says ecosystems with no more than one pressure. In paragraph E, the passage says sites with single threats recovered in less than 20 years, which matches the idea of one pressure.
Passage Reference: Sites that experienced single threats typically recovered in less than 20 years.
Common Mistake: Some students write 56 years because they see a number nearby. That refers to ecosystems with more than one pressure, so this is a wrong section trap.
Paraphrasing: Passage: 'single threats typically recovered in less than 20 years' = Summary: 'no more than one pressure'
Tips: Underline numbers in the passage and always check what condition they refer to.
Key Vocabulary:
- pressure = stress
- recovery = return to normal
Question Focus: Identifying what companies may understate
Correct Answer: damage
Passage Reference: This may have allowed, for example, an oil company to produce a report that plays down the damage done by a spillage.
Why this is correct: The critics say an oil company might produce a report that plays down the damage done. The summary paraphrases this as understating what they have caused.
Common Mistake: Students may write spillage or oil spill, but the question asks what is understated, not the event itself. This is a context shift trap.
Paraphrasing: Passage: 'plays down the damage done' = Summary: 'understating the they have caused'
Tips: Check whether the gap needs the cause or the result.
Key Vocabulary:
- plays down = makes seem smaller
- damage = harm
Question Focus: Identifying what has not been achieved
Correct Answer: ecological recovery
Passage Reference: Critics also question whether total ecological recovery really has been achieved as often as Ms Jones and Dr Schmitz suggest
Why this is correct: The passage says critics question whether total ecological recovery has been achieved, and gives the cod fishery as an example where it has not happened.
Common Mistake: Some students write only recovery. That loses the key idea of ecological, so this is a partial truth trap.
Paraphrasing: Passage: 'total ecological recovery' = Summary: 'complete ___'
Tips: When the question says 'complete', look for adjectives that qualify the noun.
Key Vocabulary:
- ecological = related to ecosystems
- collapse = fail completely
Question Focus: Identifying Dartmoor's original state
Correct Answer: forest
Passage Reference: But it is in its current state, rather than as the forest it once was
Why this is correct: The passage explains that Dartmoor is currently preserved in its present form, not as the forest it once was.
Common Mistake: Students may write wilderness because that word appears earlier. That describes how people see Dartmoor now. This is a time/tense trap.
Paraphrasing: Passage: 'forest it once was' = Summary: 'originally a ___'
Tips: Watch for phrases like 'once was' to find original conditions.
Key Vocabulary:
- pristine = untouched
- construction = man-made
Question Focus: What people want to preserve or return
Correct Answer: landscapes
Passage Reference: Ms Jones and Dr Schmitz suggest, and point to examples where it manifestly has not, such as the cod fishery of the Grand Banks, off the coast of Newfoundland, which collapsed in 1992. Almost two decades on, the cod show no sign of recovery, perhaps because new predators, such as dogfish, now dominate the waters. H. It is true, though, that the question of what is pristine or natural can be debatable. A good example of this, which Mr Weisman uses in his book, is Dartmoor, a national park in the south-west of England. Dartmoor is considered by many to be one of Britain's great nature wildernesses. In fact, it is a human construction, formed by tens of thousands of years' worth of alterations such as burning and agriculture. But it is in its current state, rather than as the forest it once was, that people wish to preserve it. Ms Jones and Dr Schmitz point out that most conservation work is not actually concerned with returning landscapes to their natural or prehuman states and 'instead use contemporaneous reference systems as targets'.
Why this is correct: The passage states that conservation work focuses on returning landscapes to present-day reference systems.
Common Mistake: Some students write ecosystems, which is mentioned a lot. But the sentence here is specifically about landscapes. This is a wrong section trap.
Paraphrasing: Passage: 'returning landscapes' = Summary: 'interested in preserving or returning ___'
Tips: Do not replace the passage word with a general synonym.
Key Vocabulary:
- landscape = area of land
- preserve = protect
Question Focus: Original condition of landscapes
Correct Answer: states
Passage Reference: most conservation work is not actually concerned with returning landscapes to their natural or prehuman states
Why this is correct: The passage contrasts present-day targets with original prehuman states, which the summary shortens to original states.
Common Mistake: Students may write conditions. That is a synonym but not the exact word. This is a synonym trap.
Paraphrasing: Passage: 'prehuman states' = Summary: 'original ___'
Tips: Always copy the exact word from the passage, not your own synonym.
Key Vocabulary:
- prehuman = before humans
- state = condition
Question Focus: Problems mentioned before optimism
Correct Answer: targets
Passage Reference: Despite their study's limitations, and the difficulty of measuring recovery and choosing target
Why this is correct: The final paragraph mentions difficulties with measuring recovery and choosing targets, which the summary shortens to problems with targets.
Common Mistake: Some students write limitations because they see it earlier. That is too general here. This is a partial truth trap.
Paraphrasing: Passage: 'choosing targets' = Summary: 'problems with ___'
Tips: Look for nouns that follow verbs like 'choosing' or 'measuring'.
Key Vocabulary:
- target = goal
- measurement = judging size or amount
Question Focus: Who feels optimistic
Correct Answer: conservationists
Passage Reference: Ms Jones's and Dr Schmitz's findings are good news for conservationists.
Why this is correct: The passage clearly says the findings are good news for conservationists, which matches the summary.
Common Mistake: Students may write researchers or scientists, but the passage specifies conservationists. This is a context shift trap.
Paraphrasing: Passage: 'good news for conservationists' = Summary: 'source of optimism for ___'
Tips: When the passage says 'good news for', the answer is usually the group named right after.
Key Vocabulary:
- conservationist = person who protects nature
- optimism = hope
General Tips:
- Summary completion questions follow passage order. Use the location of the last answer to find the next.
- Always check the word limit. Extra words are automatically wrong.
- Copy the exact word or words from the passage. Synonyms are not accepted.
- Use grammar clues around the gap to decide if you need a noun, verb, or adjective.
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