How do white saxaul and black saxaul grow in areas with different groundwater depths?

In the Karakum Desert, the distribution of saxaul species is determined by the availability of groundwater:

• White saxaul (Haloxylon persicum) is the characteristic vegetation in regions where underground water is found at deep levels.1
• Black saxaul (H. aphyllum) thrives in areas where the groundwater is located closer to the surface.1

These shrubs and trees are vital components of the desert ecosystem, providing essential hay for livestock such as camels, sheep, and goats during the winter months.1