The Dark Lord didn't have any desire or plans for environmental destruction.
The Dark Lord planned to gain control over the wizarding world, and later to subjugate or destroy the Muggles, and anyone else who wouldn't comply with his rule. However, his main goal was to assure himself power and immortality. He didn't destroy anything unless it furthered his goal somehow. In no situation do we see him destroy the environment, and what he does destroy (like buildings) is all done in order to achieve his ends of power to immortality. He is cunning, and environmental destruction does nothing to further his goals of ruling over the wizarding world, superiority over the Muggles, or preventing his own death.
For example, he killed unicorns in the Forbidden Forest, but that was in order to use their blood to strengthen themselves. His followers, the Death Eaters, don't cause much environmental destruction either. We see a Death Eater kill an animal, she thought it might have been a wizard spy.
Wizards born to Muggles may be treated less well than pure-blood wizards.
The Dark Lord despised Muggles most, but he also held wizards born to Muggles in fairly low regard. He considered wizards like Tonks, who was born to a mother who married a wizard whose parents were both Muggles, lesser.
However, this may have limited effect on those who take his side.
It seems important to note that the wizards he wanted to kill that weren't pure-bloods were mostly actively working to stop him from ever controlling the wizarding world. Severus Snape, a half-blood, was allowed to join the Death Eaters and was one of the Dark Lord's most trusted. It's entirely possible that the Dark Lord would have less strict views on not pure-blood wizards who were willing to accept his leadership over the wizarding world.
