With previously unknown insect and disease species increasingly impacting our favorite trees (ash,elm,oak etc.), “species diversification” makes ecological as well as economic sense. Ideally, no particular tree species should ever comprise more than 5% of the total tree population for a given area. Following that, no particular tree genus (eg.maples) should ever comprise more than 20% of the total population for a given area.
To help achieve a desired uniformity of shapes, heights and textures in a boulevard/parkway tree scenario, similar shaped cultivars, but those of a different genus should be combined. Little Leaf Linden combined with Turkish Filbert would be an example.
Obviously, the best tree species/genus percent ratio can’t be achieved overnight, but efforts towards the goal can be started with the proper selection of genus and species at the time of deciding what type of tree to plant. This increasingly makes the best economic and ecological sense for the future.
Harold Hoover, Board Certified Master Arborist