Mongabay: The demand for a rare, fragrant ingredient is threatening the survival of one of the world’s most expensive trees, a new Al Jazeera documentary has found. Some trees of the Aquilaria and Gyrinops genus — found in parts of India and southeast Asia — produce agarwood, a resin-soaked, scented bark. Oil from this fragrant agarwood is frequently added to perfumes, incense products, and medicines, and is an integral part of many cultures. Agarwood (also called oud) is especially popular in the Arab countries…