Question

Soil classification is partially determined by the presence of organic material, such as humus. Which would have more humus—a desert or a forest—and why? Check all that apply.

a forest because it has more trees to provide plant litter
a desert because it has soil with a larger particle size
a forest because it has more animals to mix the soil
a forest because the trees prevent rain from reaching the soil
a desert because the dry air decomposes plant litter

Answer 1

Correct answers:
- a forest because it has more trees to provide plant litter
- a forest because it has more animals to mix the soil

Why: Forests produce lots of leaves, twigs and roots (plant litter) that become organic matter, and they support many soil organisms (earthworms, microbes, insects) that mix and transform that litter into humus.

Why the others are wrong:
- Larger particle size in deserts tends to reduce humus accumulation (less surface area and water retention), so that reason does not make deserts richer in humus.
- Trees do not “prevent rain from reaching the soil” in a way that increases humus; forests usually have more moisture available for vegetation and decomposition.
- Dry desert air actually slows decomposition (reducing humus formation), it doesn’t increase it.