When I ask this question, I mean it in a sense of how nature is progressing in the Fallout universe. I was personally very disappointed by the lack of flora in Fallout 3. Washington D.C is situated on swampland in RL, so why hadn't it returned to a state reflecting that after 200 years? To be honest, Metro Last Light showed what I had believed D.C would look like after all those years.

https://www.youtube.com/watch?v=5mOr8-I2H70

Furthermore, the worlds have been static and do not convey the sense of having a true ecosystem. As shown in the video, Metro pulled it off even without actually being an open world game.

My question is, have the nuclear weapons been destructive to the point of rendering zones unable to grow vegetation of some sort? Fallout NV was also very dry, but as it was in a desert i suspect that was the point . Every Fallout game has seemed dry and lifeless in terms of wildlife and flora. Is it the engine limiting this or does lore explain why things are not returning to a (semi) usual state?

This post is mostly targeted at FO3 and I brought this up due to concern that Bethesda might create a barren, dry husk for world spaces in the future. Is that the future of Fallout or will it diversify?

(Also, i played the original games and i duly note the presence of various plants )

This is a common complaint about Fallout 3. It has been talked about to death and normally breaks down into a Fallout 3 vs every other Fallout. Hopefully it won't happen this time.

But as for your question. No the Fallout world is not dead. Plant life is common in all the Fallouts but for Fallout 3 aside from Oasis and Point Lookout and brown dead grass/shrubs.

There is no reason given as to why plant life wasn't included, as in living trees and agriculture. Plant life in the Fallout Universe and in real life isn't permanently killed off by radiation. It seems that Bethesda decided to do what they did to give a hopeless feel to the world that everything is dead.

Possibly because the screaming we heard that FO3 was just Oblivion with guns would've been even louder than it already was.

I do remember that there was a mod for FO3 which included some shruubery and trees to the wasteland. It helped to make a dreary dead world a little less depressing.

Here's hoping we don't have a carbon copy of a dead lifeless world this time, like we did the last time around.

And not one attributed to Harold the Magic Tree Mutant and the Lone Wanderer.

It's something I suspect was part of the reason as to why things were made lifeless. So they could work Harold into the story so we as the player can "Bring Life to the Wasteland!"