during the day, trees provide significant shade by intercepting solar radiation, reducing mean radiant temperature (up to 16 °C)
Sadly they work the opposite way at night, they don't allow SPACE to cool the ground. A textil/plastic plate moved automatically can provide more cold, if that's the goal.
It really depends on how broad and high the tree canopy is; you don’t need super high tree density to provide a lot of shade.
The main benefit over other solutions is that properly selected trees require very little upkeep from humans, unlike anything mechanical or requiring movement. Though I imagine that is less the case in Vegas.
