I mashed up two tweets together and I made some edits for clarity.

A mature saguaro takes 125 years to grow. They keep going down around Phoenix. [...] Saguaros open tiny pores on their skin at night to take in CO2. When it's too hot overnight, they can't do it. [...] It's happening all over South Mtn too. Saguaros are native there.

Nitter

Another reply...

There's also potentially some heat stress from underground issues with the construction and lack of shade. You can see that out in east valley or scottsdale- stressed out saguaros on one side and perfectly healthy, normal flowering and fruiting on the other side of the road in undeveloped acreage.

We could use more shade (especially the leguminous trees).