If there was anything that would get the far-left out of bed with the Islamofascists, it would be jihadis starting forest fires. Executing homosexuals, stoning and beating innocent women, Sharia Law, mutilation of female genitals, death penalty for pornography, concubine slavery, criminalization of the teaching of evolution, criminalization of fornication, no freedom or speech or freedom of religion, etc etc etc just isn't enough. But to attack innocent trees, animals, or other parts of the environment, is an assault on their RELIGION, the very basis of their faith, their salvation, their meaning of life. Attacking the prime symbols of American militarism and capitalism on 9/11 endeared the left to Islamofascism. IMO, they would feel betrayed if nature was attacked. /rant
I think you may be underestimating the left's capacity for selective outrage.
The Islamic arsonists, as poor oppressed dark skinned people, would never be held responsible for their own actions by the left. To do so would be considered racist. Also, the left thinks that America deserves to be attacked because of the BusHitler regime's crimes against humanity. Whoever lit the fires, the subsequent spotted owl crisps would be, as they say, Bush's fault.
I think that your hypothetical event would be a non-event to the left. Just like 9/11.