Step 1: Understanding the Concept:
The choice of agroforestry tree species in arid regions is dictated by their drought tolerance and their capacity to yield high-quality forage (fodder) for livestock during dry seasons.
Step 2: Detailed Explanation:
1. Prosopis cineraria (Khejri) is the most valuable multipurpose tree species of the hot Indian desert (Thar desert).
2. It plays a vital role in desert agroforestry because it is a deep-rooted phreatophyte that does not compete with shallow-rooted crops for surface water.
3. Its highly nutritious leaves, locally called "loong," are lopped annually to provide excellent, green, protein-rich forage for sheep, goats, and camels during the dry summer months.
4. The other options are suited to different ecological zones: Quercus glauca (temperate hills), Salix tetrasperma (wetlands/riparian), and Schleichera oleosa (tropical moist/dry deciduous).
Step 3: Final Answer:
The premier fodder tree of the Indian desert is Prosopis cineraria.