The following table shows six tropical forests, arranged from least to most fertile soils, estimated from total soil nitrogen.
| Parameter | Lower montane rainforest, Puerto Rico | Amazon caatinga, Venezuela | Oxisol forest, Venezuela | Evergreen forest, Ivory Coast | Dipterocarp forest, Malaysia | Lowland rainforest, Costa Rica |
| Above-ground biomass (metric tons/ha) | 228 | 268 | 264 | 513 | 475 | 382 |
| Root biomass (metric tons/ha) | 72.3 | 132 | 56 | 49 | 20.5 | 14.4 |
| Total soil nitrogen (kg/ha) | –– | 785 | 1697 | 6500 | 6752 | 20 000 |
| Turnover time of leaves (years) | 2 | 2.2 | 1.7 | –– | 1.3 | –– |
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INTERPRETATION
Which two areas have the poorest soils, in terms of nitrogen availability?
Look at the root biomass in the two areas from Question 1. What is the relationship between root biomass and poor soils? Propose an explanation.
Can you determine soil nutrient levels by looking at the above-ground biomass? Explain.
ADVANCE YOUR THINKING
Notice how long it takes leaves to break down (“Turnover time of leaves”). Speculate as to why trees in poorer soils produce leaves that last longer.
If you removed the trees through logging or burning, would these areas be good for agriculture? (Hint: Cleared areas are usually used for small farms that do not have funds to purchase farm equipment, fertilizers, or other chemicals.)