Crown Duel by Sherwood Smith
A Covenant and a Code
Hundreds of years ago, the mysterious Hill Folk went to war with the people of Remalna to defend their groves of colortrees, whose rich hues of blue and red and gold made them valuable for trade. The Hill Folk fought back with their all of their magical powers and easily defeated their foes. At last a truce was reached. The Remalnan settlers would cut no more wood, and in exchange the Hill Folk would give magical Fire Sticks to last them the winter.