The affix aṇ comes in the sense of 'modification or part' (provided that the word has not the anudātta - grave accent on the first syllable).,
Thus देवदारवम्, भाद्रवारवम् ॥ The words देवदारु and भद्रदारु are ady-udatta owing to Phit Su. II. 14 (पीतद्र्वर्थानाम् -- the trees denoting soft timber trees have acute on the first).,