The bottom line with arid climates is that the soil is marginal, and we humans tend to make it more marginal by doing certain things. Such as gathering wood or chopping down trees in places where they are already scarce, decreasing the amount of humus, and making it more difficult for plants to grow. Or such as pumping too much water, drying the soil further and making it less likely for plants to grow. These practices can lead to desertification , the process of continually decreasing vegetation in a certain area. C. Wet, hot climates.
Examples are tropical rainforests.
Here we have lots of trees. There are so many trees, they suck up nutrients from the soil at a furious rate, destroying humus. So we get thick soils. The large amounts of rainwater leach the soil effectively, and this destroys all but a few minerals. Even quartz is destroyed by weathering.