What Is Productivity Per Day Per Unit Leaf Area?

Productivity per day per unit leaf area measures how efficiently each square meter of leaf surface produces biomass each day. This metric helps ecologists compare the photosynthetic efficiency of different ecosystems, regardless of their total leaf cover or growing season length.

Comparing Hot Deserts, Temperate Forests, and Tropical Forests

1. Hot Deserts

• Leaf Area: Low, as plant cover is sparse.

• Growing Season: Very short, limited by water availability.

• Daily Productivity Per Unit Leaf Area: Can be high during brief growing periods, but when averaged over the year and all leaves, it is generally the lowest among the three ecosystems.

• Annual Productivity: Very low due to harsh conditions and limited plant cover.

2. Temperate Forests

• Leaf Area: High, but seasonal—leaves are present only during the growing season.

• Growing Season: Moderate, limited by winter.

• Daily Productivity Per Unit Leaf Area: Intermediate. High during the growing season, but lower than tropical forests when averaged over the year.

• Annual Productivity: High, but less than tropical forests due to seasonal limitations.

3. Tropical Forests

• Leaf Area: High and present year-round.

• Growing Season: Year-round, thanks to stable temperatures and moisture.

• Daily Productivity Per Unit Leaf Area: Highest, as leaves are continuously active and conditions are optimal for photosynthesis.

• Annual Productivity: Highest among terrestrial ecosystems.

Correct Increasing Order

Based on global ecological data and syntheses, the correct increasing order for plant productivity per day per unit leaf area is:

Hot deserts < temperate forests < tropical forests

This reflects the fact that tropical forests have the highest daily productivity per unit leaf area due to their continuous growing season and optimal conditions, while hot deserts have the lowest due to extreme stress and limited growing time.

Evaluating the Options

Let’s review the options:

1. Tropical forests, hot deserts, temperate forests

   • Incorrect. Tropical forests have the highest productivity, not the lowest.

2. Hot deserts, temperate forests, tropical forests

   • Correct. This matches the standard ecological understanding.

3. Hot deserts, temperate grasslands, tropical forests

   • Not listed in your original question, but if present, grasslands can be intermediate, but forests are generally higher than grasslands when averaged over the year.

4. Tropical forests, temperate grasslands, hot deserts

   • Incorrect. Tropical forests have the highest productivity, not the lowest.

Conclusion

The correct increasing order for plant productivity per day per unit leaf area is:

Hot deserts < temperate forests < tropical forests

Correct answer:
(2) Hot deserts, temperate forests, tropical forests