1. Bring 4 cups water to boil; add wheat berries. Reduce heat and cook, uncovered, for 1 hour or until tender and most of liquid is absorbed. Drain; set aside.
2. Cook carrots and celery in 1 teaspoon oil in a large skillet over moderate heat for 3 minutes or until tender. Add wheat berries and cranberries, and cook, stirring, for 5 minutes or until hot. Transfer to serving bowl, and stir in next 4 ingredients (through pepper). Cover and keep warm.
3. Preheat oven to 450°. Brush a baking sheet with 1 teaspoon olive oil; arrange salmon, skin side down. Combine maple syrup and mustard; spread on top of salmon. Roast in middle of oven for 7 minutes. Turn broiler on; broil salmon for 3–4 minutes or until golden on top. Transfer salmon to a cutting board, and cut half of it into 4 (6-ounce) pieces; reserve the rest.
4. Reserve 1 1/2 cups wheat berry mixture. Stir mâche into the remaining wheat berry salad. Serve each piece of salmon on top of salad.