I am standing in the shadow of General Motors' $1 tree. It's a native guaricica, with pale white bark and a spreading crown that looms about 40 feet above my head. Hanging from its trunk is a small plaque that identifies it as tree No. 129. I've come here, to the verdant chaos of Brazil's Atlantic forest, to understand the far-reaching and politically explosive controversies taking shape in diplomatic corridors thousands of miles away over the fate of trees like this one.