The development of forest ecosystems is usually characterized as an in

Question

The development of forest ecosystems is usually characterized as an internally regulated (endogenous) progression in which certain kinds of plants replace others sequentially. If a forest ecosystem remains free for a long time of external (exogenous) Catastrophic disturbances such as major fires, its development culminates in a steady-state condition in which there is no net change in the biomass. However, some researchers hypothesize that North American forest ecosystems have rarely attained a steady state, even prior to the period of extensive human intervention. According to this view, known as the recycling hypothesis, fires truncated the endogenous development of these ecosystems, moving them back to an earlier developmental state, and net changes in the biomass occurred in waves, with rhythmic rises followed by falls chat were triggered by fires occurring at relatively short intervals. For example, in 1970 Loucks suggested that, prior to the establishment of settlements in the midwestern United States by European emigrants, forests in Wisconsin burned repeatedly, at relatively short intervals ranging from several decades to about a century. Reliable evidence on the intervals between major fires has confirmed that this pattern of recycling occurred throughout the Great Lakes region.

Nevertheless, the waveform configuration of exogenous disturbances does not appear to have been the rule throughout North America. Reliable evidence for the province of New Brunswick, Canada, indicates that there were intervals of 650 to 2,00O years between major fires in large forests, and reliable evidence for the White Mountain National Forest in the northeastern United States also reveals very long periods between fires. Large areas of presettlement forests in these territories were free of catastrophic disturbances for durations that would have been sufficient for their ecosystems to attain a steady—state condition.

It seems, then, that prior to settlement by Europeans, both endogenous attainment of a steady state and catastrophic recycling occurred in Nonh America. Because of modest levels of exogenous disturbance or long-time intervals between large-scale disturbances, forested regions of the humid temperate mountains of the northeastern United States might have been centers where there were relatively high probabilities of attaining steady—state conditions. In almost every direction away from these centers, recycling would have taken on greater importance. Of course, subsequent human intervention has blurred this larger picture somewhat. Land clearings in some sections of the northeastern United States resulted in a pattern of recycling that is quite similar to that thought to characterize those ecosystems that were subjected in the past to severe exogenous disturbances at-short intervals. On the other hand, in some areas that had been naturally prone to exogenous disturbances, the suppression of fires has allowed for progression toward the steady state, helping to bring about a condition that was seldom achieved previously.    1 
 1. According to the passage, a forest ecosystem that is in a steady-state condition has been

(A) continuously in that condition for a relatively short period
(B) exhibiting net changes in its biomass for a relatively short period
(C) burned by fires that selectively destroyed certain kinds of plants and spared others
(D) brought to that condition by a recent major external disturbance
(E) undisturbed by destructive external influences for a long period

2 
 2. The author implies that the recycling hypothesis is not

(A) consistent with the waveform pattern of exogenous disturbances to forest ecosystems
(B) amenable to testing because the evidence on intervals between major fires in presettlement forests is of unknown dependability
(C) relevant to the question of whether the forests of North America have universally attained a steady-state condition
(D) plausible for any forest that is located outside of the Great Lakes region
(E) valid as an explanation for the development of the ecosystems of all North American forests

3 
 3. The author implies that there is factual support for the conclusion that a steady-state condition occurred in which of the following presettlement forests?

I. Those of the Great Lakes region
II. Those of the province of New Brunswich Canada
II. Those of the White Mountain National Forest

(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II and III

4 
 4. According to the recycling hypothesis, major exogenous disturbances of forest ecosystems have

(A) initiated a period of endogenous development in which the usual sequence of plant successions is altered
(B) provided settlement sites for Europeans who migrated to North America
(C) returned the forest ecosystem to a prior developmental state
(D) accelerated the normal pace of endogenous development
(E) triggered major fires that permanently reduced the net biomass

5 
 5. The passage supplies information for answering all of the following questions regarding forest ecosystems EXCEPT:

(A) Do major forest fires ever move a forest's ecosystem back to its initial developmental state?
(B) Is it likely that some North American forests will have progressed toward a steady-state condition during the twentieth century?
(C) Is the steady—state condition signified by no net change in the biomass over time?
(D) Have scientist been able to determine the frequencies with which major fires occurred in certain forests in the past?
(E) Is there evidence that any forest ecosystem has exhibited a waveform pattern of net changes in its biomass?

6 
 6. The author refers to evidence on the frequencies of major fires in different regions of North America in order to

(A) show that such evidence is most reliable for those centers where the probability of attaining a steady-state condition had been especially high prior to their being settled
(B) explain why the early European emigrants preferred to settle in the midwestern United States rather than in the mountainous regions of the northeastern United States
(C) cast doubt on the view that certain northeastern forests probably attained a steady-state condition prior to their extensive settlement
(D) provide support for linking a forest's geographical location with its probability of attaining a steady—state condition prior to the period when it was setteled
(E) call attention to variations among regions of North America in the effusiveness with which modern techniques of preventing forest fires have been applied

7 
 7. The information in the Passage supports that the author regards the claim that North American forest ecosystems have rarely attained a steady—state condition with

(A) dismay, arising from the author's belief that the clam has led to irreparable damage
(B) indignation, arising from the author's inference that the claim is based on a logical fallacy
(C) skepticism, arising from the authors’ awareness of certain facts that negate the broad scope of the claim
(D) confusion, arising from the author's awareness that some evidence does not support the claim even though other evidence appears to do so
(E) approval, arising from the author's belief that the claim is fully supported by reliable evidence

8 
 8. The author implies that human activity subsequent to European emigration to North America has resulted in which of the following consequences for North American forests?

(A) Reforestation methods that were abandoned by Europeans when they first began to emigrate to North America have been reimplemented.
(B) A steady-state condition that was seldom achieved previously in the White Mountain National Forest has been brought about in that region.
(C) Forest conservation practices that had proven to be successful in the midwestern United States were effectively extended to the mountainous regions of the northeastern United States.
(D) The internally regulated developmental sequence of plant successions has been protected against major fires in some North American forests.
(E) The endogenous progression in which certain kinds of plants replace others in succession has been truncated by landclearing practices in most of the forests of the mountainous regions of the northeastern United States.

Sajjad1994 · Answer

Explanation

1. According to the passage, a forest ecosystem that is in a steady-state condition has been

First locate the definition of  “steady-state condition”  in the passage.  Lines 4–7  explain this:

"If a forest remains free for a long time of catastrophic disturbances (fires, etc.), its development culminates in a steady-state condition in which there is no net change in the biomass".  Hence No net biomass change + free of catastrophic disturbances for a long time.

(A) continuously in that condition for a relatively short period 
Contradicts  “for a long time”  from the passage, wrong.

(B) exhibiting net changes in its biomass for a relatively short period 
Says the opposite: steady state = no net biomass change, so wrong.

(C) burned by fires that selectively destroyed certain kinds of plants and spared others 
That’s an external disturbance, steady state occurs when there are no major fires for long enough; fires would disrupt steady state. So wrong.

(D) brought to that condition by a recent major external disturbance 
Recent disturbance would reset the succession, that would be moving toward steady state, not being in it yet. Passage says it’s reached after long freedom from disturbances. Wrong.

(E) undisturbed by destructive external influences for a long period 
This matches exactly: long period without catastrophic disturbances ----> steady state.

Answer: (E)

rjg_25 · Answer

Can someone please explain the 5th question. Thank you!

guddo · Answer

5. The passage supplies information for answering all of the following questions regarding forest ecosystems EXCEPT:

The passage contrasts two patterns: steady state when there are very long intervals without major fires, and recycling when fires happen often enough to push ecosystems back to earlier stages. It says reliable evidence shows short fire intervals in the Great Lakes region and very long intervals in New Brunswick and the White Mountains, and it adds that human actions later sometimes increased recycling (land clearing) and sometimes encouraged movement toward steady state (fire suppression).

(A) Do major forest fires ever move a forest's ecosystem back to its initial developmental state?

The passage says fires can move an ecosystem back to an earlier developmental state, but it never says back to the  initial  state. “Earlier” could be many stages short of the beginning. So the passage does not supply enough information to answer this.

(B) Is it likely that some North American forests will have progressed toward a steady-state condition during the twentieth century?

Yes. The passage says that in some areas, suppression of fires has allowed progression toward the steady state. That supports a yes answer for at least some forests during the period of modern human intervention.

(C) Is the steady-state condition signified by no net change in the biomass over time?

Yes. The passage explicitly defines steady state that way.

(D) Have scientists been able to determine the frequencies with which major fires occurred in certain forests in the past?

Yes. It gives “reliable evidence” about intervals between major fires for multiple regions, which is exactly about frequency.

(E) Is there evidence that any forest ecosystem has exhibited a waveform pattern of net changes in its biomass?

Yes, in the way the passage frames it. It describes the recycling hypothesis as involving wave like biomass changes and then says reliable evidence confirmed that this recycling pattern occurred throughout the Great Lakes region.

Answer: (A)

The development of forest ecosystems is usually characterized as an in

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The development of forest ecosystems is usually characterized as an in

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