These are tough times for environmentalists, what with the Bush administration's frontal assault on environmental policy, drastic funding cuts and layoffs in state environmental programs, and the aftermath of a war in Iraq fought, in the opinion of many, over our nation's undying addiction to oil. It's thus fitting, if somewhat disheartening, that along come two books whose central message is that it's not easy being green, no matter what the circumstances. Bronx Ecology By Allen Hershkowitz Island Press, 200 pages, 2002 Allen Hershkowitz's Bronx Ecology: Blueprint for a New Environmentalism and Lis Harris's Tilting at Mills: Green Dreams, Dirty …