Minimalist must be a vegan?

Not necessary. But a vegan could be a minimalist.

Some minimalists are care about environment. They practice minimalism to prevent themselves spending too much on unnecessary, which will be ended up in the landfill and cause more land to be exploited for trash management purpose. With decreasing number of trees our global warming effect will become worst.

As reviewed by some scientists animal farming actually play the main role to the climate change. As larger land needed for animal farming and more agriculture land needed to feed the animal. You could imagine how much of trees need to be scarified.

A non-vegan need few farming lands and more agriculture lands to feed him/her, but a vegan just need few agriculture lands to feed.

So, I could say a vegan is definitely a minimalist to the environment, as they don't exploit too much land on earth compare to non-vegan.