I'm not sure that environmentalism is necessarilly a strictly leftist domain. I'd say that those environmentalists opposed to technological or industrial advancement, even at the cost of human happiness are fairly reactionary.
I think in Germany, they have a National Socialist Green party. Their flag is a swastika on a green background.
True- environmentalism is definitely not a left-wing-only ideology. In the US, it's predominantly left-wing because
1) The New Left embraced it, and got on early with the first Earth Day, which was modeled off of teach-ins against the war and attracted much of the same crowd
2) the anti-environmentalist movement (Wise Use Movement) from the right rose during the Reagan presidency and that along with the rest of the 'ownership society' mentality more or less set GOP positions on the environment to be 'ignore environmental problems and market failures at all cost because admitting they exist would jeopardize adherence to our economic ideology'.
Thanks to that, what started as something that could have resembled a new domestic consumer safety twist (DDT is harming our kids!) on the old preservationist (Save Yosemite!) and conservationist (Replant after logging!) movements developed into a more left-aligned concern. That said, the environmental movement is *extremely* diverse, ranging from 'free market environmentalism' to eco-socialism and Bookchinite social ecology, from Deep Ecology to anthropocentric reformism, and from primitivism to Bright Green techno-positivism. Being an environmentalist just means that you're concerned with the environment- and not all environmentalists even agree on what parts to be concerned about, as some place much more value on 'simple' sustainable resource use while other focus on maintaining more habitat for nonhuman life or on a holistic vision of maintaining the whole ecosystem in a more or less stable state. What *kind* of environmentalist you are depends entirely on how you *conceive* the problem and your *response* to it. Representing environmentalists as a single ideology because they all care about the environment would be like representing 'people who are concerned about the economy' as a single ideology- which would be ridiculous because everyone with an iota of sense has an opinion or some concern over the economy (just as anyone with an iota of sense has concern for the environment- yes, I am stating that those who outright ignore the environment have not a lick of sense).
So, with all that diversity, naturally, you're going to get someone who is 1) a fascist and 2) concerned with the environment- which is frankly not surprising at all because fascists already hold an ideology that stresses the organic unity and wholeness of the nation-state, so stressing the organic wholeness and unity of the nation-state's ecosystem shouldn't be too hard. Plus, some Deep Ecologists (as in, the Deep Ecologists who are total turds) have some frankly troublingly fascistic ideas (which is a source of huge disagreement between them and... pretty much everyone else). The Social Ecology camp (super-democratic socialistic 'communalist' environmentalists taking a lead largely from Bookchin) alleges that Deep Ecologists, Ecosophists, and Ecofascists share a lot of common ground and membership and feed one another. That all said, let's not tar Deep Ecology with guilt by association, because their points still deserve a fair trial by public opinion. But, yeah, ecofascists are a thing- albeit an extreme fringe minority in the environmentalist movement. The majority of the environmental movement is reformist, progressive, and basically liberal 'light/lite green' techno-optimist sort of stuff, followed by the more techno-skeptic and techno-phobic (there's a big difference) branches, which tend to be more biocentric, and with probably the third largest camp consisting of the green left environmental justice people. I'd say ecofascists are probably the smallest significant fringe group, ranking after primitivists.
Edit: Also, the Libertarian National Socialist Green Party is American. One of their fans/members was involved in the Red Lake shooting, IIRC.