As agricultural crops go, trees are difficult. Many tree species are wind-pollinated, making selective breeding exceptionally difficult. Many trees don\u2019t get large or old enough to show desirable traits until many years after planting, making breeding for any particular characteristic a slow and resource-intensive process. For much the same reason that elephants, parrots and other long-lived animals can be tamed but have never been as domesticated as dogs, cats or cattle, engineering most tree species to serve human needs is the work of generations, almost impossible to do in human timescales using conventional breeding techniques. Forestry faces all of these challenges and more, due to limited genetic information about trees farmed for paper or meant for restoring natural forests after blights or clear-cutting.<\/p>\n