Christmas tree cultivation major Christmas tree growing region, Douglas-fir has always been the primary species grown. A full one-half of all trees produced in the Pacific Northwest are Douglas-fir. Douglas-firs typically take five to seven years before they are mature enough to sell as Christmas trees. Also common in the region are noble fir, a tree which commands a higher price than Douglas-fir, and grand fir, which accounts for about 10 percent of the annual harvest in the Northwest. Other species collectively account for only 3–5 percent of the total Northwest harvest. In North America, Fraser fir, grown in the Appalachian Mountains of
WAVL tree red–black tree, because they would in effect cause the recoloring of large subtrees of the red–black tree rather than making color changes only on a single path in the tree. This allows WAVL trees to perform fewer tree rotations per deletion, in the worst case, than red-black trees. WAVL tree In computer science, a WAVL tree or weak AVL tree is a self-balancing binary search tree. WAVL trees are named after AVL trees, another type of balanced search tree, and are closely related both to AVL trees and red–black trees, which all fall into a common framework of rank balanced