Forests are the planet's biggest terrestrial carbon sinks, absorbing and storing a quarter of the world's annual emissions. Forests are...
GMAT Reading Comprehension : (RC) Questions
Forests are the planet's biggest terrestrial carbon sinks, absorbing and storing a quarter of the world's annual emissions. Forests are also vulnerable to changes in climate, leading scientists to explore whether they can continue their sequestering magic in a warming world.
As global temperatures rise, forests face counteracting carbon processes. Warming causes dead plants to decompose more quickly, which releases carbon dioxide. But decomposition also releases ammonium—essentially fertilizer—into the soil, allowing trees to grow faster and store more carbon.
To find out which process wins out, an ecologist tracked two 10,000-square-foot plots of deciduous forest for seven years. On one plot, he installed underground cables to warm the soil by 9 degrees Fahrenheit. This hotter soil, rife with decaying plants, released significantly more carbon than did its cooler counterpart. That carbon burst was short-lived, however. As the heated soil's ammonium levels increased, trees grew faster and absorbed more carbon. By the study's end, the warm plot's trees were sequestering carbon at the same rate as the soil was emitting it.
Unfortunately, trees' growth rate is limited, unlike the rise in temperatures. Once that growth rate trails off, additional carbon released from the ground will enter the atmosphere and cause the planet to be warmed.
According to the author, the study described in the passage was prompted by
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| "Forests are the planet's biggest terrestrial carbon sinks, absorbing and storing a quarter of the world's annual emissions." | What it says: Forests on land are really important for removing carbon from the atmosphere - they take in 25% of all carbon produced each year. What it does: Sets up the main topic and establishes forests as critically important to climate. Source/Type: Scientific fact Connection to Previous Sentences: This is our opening statement - no previous context yet. Visualization: If the world produces 100 units of carbon emissions annually, forests absorb 25 of those units. Reading Strategy Insight: This is a clear, straightforward factual opener. Note the specific statistic (25%) - authors often start with concrete data to establish credibility. |
- The study wasn't focused on determining maximum growth rates - it was testing which of two competing processes would dominate
- The passage shows the scientist was comparing heated vs. normal soil effects, not measuring maximum possible growth
- Growth rate limitations are mentioned only as a concluding insight, not the original motivation
- The study wasn't trying to increase carbon sequestration - it was testing whether current levels could be maintained
- The research question was about understanding natural processes under warming, not enhancing forest performance
- The experimental design (comparing normal vs. heated plots) was diagnostic, not aimed at optimization
- The growth rate limitation is presented as a discovery from the study, not what prompted it initially
- This limitation appears at the passage's end as the author's extension of the findings, not the original research motivation
- The timeline shows this realization came after observing the experimental results
- The passage explicitly states the study aimed "To find out which process wins out" between two "counteracting carbon processes"
- These counteracting processes (faster decomposition vs. fertilizer effects) are described as the core scientific uncertainty
- The experimental design directly tests how these competing processes affect forests under warming conditions
- The heated cable technique was the method used in the study, not what prompted conducting it
- The passage presents this as how the scientist conducted his research, not why he felt research was needed
- Technique development is a means to answer questions, not the motivation for asking them