Some of the old milpas that were carelessly overused have invited the invasion of a bracken fern that grows well after fire and shades out the forest herbs, bushes, and trees, inhibiting succession. The only way to eliminate this fern is to plant the velvet bean, called macuna. Macuna is a legume, fixing nitrogen. If planted in an area of this fern, it grows onto the ferns, using them as a trellis. After the first year the fern is diminished in extent, but the self seeding macuna will do its final job in the second year. By the third year there will be little if any of the fern, and the macuna will be shaded out by the natural succession process.