This is a tree question, not cattle

[Hippie Rancher]

I thought poplar, alamo, and cottonwood was all the same thing.

They are indeed very shallow rooted and grow near rivers or tanks. They grow fast and are the first to fall in a storm.

alamo is Spanish for cottonwood, poplars have a narrower upright growth (sort of the Italian cypress of cottonwoods) - regular cottonwoods look like giant broccoli to me

 

[dun]

The question was fastest growing, not longevity. That's the reason poplar and cottonwood do so well. There's also mimosa, they grow like weeds but you have to contend with flowers and seeds