Treesinging is an ability mostly unique to the Ogier in the modern day. It allows them to stimulate the growth of plants, usually trees, through the use of special songs. It also allows them to use different songs to control the growth and to communicate, in a fashion, with the plant; Treesingers are known to produce extremely distinctive, valuable wooden crafts. They are able to make these wooden crafts without in any way harming the tree, "pulling" the shaped wooden artifact out of the tree without hurting it. The ability seems to have dwindled in recent times; Loial is one of the most talented Treesingers in a very long time.
It can be speculated that Lews Therin, and therefore Rand al'Thor, might have some ability with treesinging as demonstrated during his meeting with Matt and Tuon in Ebu Dar.