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Difficulty: HardCommand of Evidence: Textual

Ecologist Dr. Liam O’Connor and colleagues investigated the microclimate cooling effects of urban parks. O’Connor hypothesized that urban parks with high canopy structural complexity—characterized by a wide variation in tree heights—are more effective at lowering local air temperatures during extreme heat events than parks with uniform canopy heights. O’Connor argued that this cooling advantage occurs because varied tree heights create surface roughness, generating atmospheric turbulence that mixes warm surface air with cooler upper air currents, even when parks have the same total leaf area index (LAI). Which finding, if true, would most directly support O’Connor’s hypothesis?

  1. A
    Urban parks featuring a high diversity of tree species were found to experience less canopy damage during drought events than parks with uniform species composition, allowing them to maintain consistent cooling rates over several months.
  2. B
    Computer models indicated that if urban parks with uniform canopy heights were retrofitted with artificial wind-deflection structures, the resulting air turbulence would reduce local temperatures by approximately 1.0∘C1.0^\circ\text{C}.
  3. During a heatwave, urban parks with high variation in tree heights recorded average air temperatures 1.5∘C1.5^\circ\text{C} lower than parks with uniform tree heights and equivalent LAI, and measurements showed significantly greater vertical air mixing above the varied canopies.Answer
  4. D
    An analysis of urban parks across several regions concluded that any increase in vegetation density leads to a uniform reduction in surrounding temperatures, regardless of whether the canopy heights are uniform or varied.

Answer

The finding that urban parks with high variation in tree heights recorded lower temperatures than parks with uniform tree heights and equivalent LAI, along with greater vertical air mixing.
The correct answer directly supports the hypothesis by showing that parks with varied tree heights achieved greater cooling than parks with uniform tree heights when holding total leaf area (LAI) constant, while also confirming the hypothesized mechanism of increased vertical air mixing (turbulence).

Step-by-Step Solution

1
Analyze the passage to locate Dr. O’Connor’s core hypothesis.
The hypothesis asserts that urban parks with highly varied tree heights (canopy structural complexity) cool the air more effectively than parks with uniform heights and equal leaf area, due to generated air turbulence.
This establishes the specific relationship (varied heights →\rightarrow turbulence →\rightarrow greater cooling) that the correct evidence must support.
2
Evaluate the options against the key variables.
Only the option describing the temperature differences in parks with varied vs. uniform tree heights under equivalent LAI conditions directly matches the experimental variables.
By keeping LAI constant, this option isolates canopy height variation as the cause of the cooling and directly supports the mechanism of vertical air mixing.

Key Concept

Evaluating textual evidence to support a scientific claim.
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Topics

Command of Evidence: Textual

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