“I once set fire to the woods,” Henry David Thoreau laconically confided to his journal in 1850, six years after he torched approximately 300 acres of Concord forest. Thoreau? Did the man known then and now as a tree-hugger ­actually strike a match near a clump of dry grass so he could cook a batch of freshly caught fish, blithely unaware that the spring of 1844 was unusually dry and that on that day in particular a strong wind was dangerously blowing from the south?