 " Trees " is a poem of twelve lines in strict iambic tetrameter . All but one of the lines has the full eight syllables of iambic tetrameter . The eleventh , or penultimate , line begins on the stressed syllable of the iambic foot and drops the <unk> syllable — an <unk> ( or " headless " ) <unk> line — that results in a truncated seven @-@ syllable iambic tetrameter line . Making the meter of a line <unk> can change the feeling of the poem , and is often used to achieve a certain effect as a way of changing tone or announcing a conclusion . The poem 's rhyme scheme is rhyming couplets rendered aa <unk> <unk> <unk> ee aa . 
