On a sweltering July day, 30 Kurdistan Workers’ Party fighters stripped the rifles from their backs and tossed them into a blazing fire. The symbolic ceremony last year marked the end of a decades-long conflict with Turkey. Now, one of the big lingering questions is how to repair the grim toll on the environment. Fighting in the Kurdish region, which stretches across several countries besides Turkey, left scorched forests, water contamination and declining biodiversity.