“I still remember discovering a row of small trees with a fruit like a blackberry and leaves vaguely resembling sassafras on my path to school. After a little research, I began to gather handfuls of fruit each day on my walk home.”
White mulberry (Morus alba), a fast-growing (as a seedling, four feet per year!), deciduous, medium size (generally 10 to 20 m tall) tree, was introduced from northern China to North America from the 16th to the 19th century to feed silkworms. Though my own row of trees still bore silken nests full of wriggling worms, the silk industry never came to fruition and white mulberry was here to stay, finding use as an ornamental tree and as supplemental feed for livestock in the dry season. Due to its strong branches, it is also planted as a windbreak and apparently makes a great climbing tree. It is tolerant of drought, poor soil, and pollution, so is common in urban environments. Some homeowners plant mulberry because of its propensity to attract many birds- it is a favorite food of cardinals, robins, orioles, finches, thrushes and more.
With widespread planting over more than two centuries, and continued distribution by nurseries, white mulberry has naturalized in semiurban and rural areas in most states and three Canadian provinces as well as central Asia and southern Europe. A detailed description of its invasive occurrence, by region, is found here. Rapid growth, aggressive and deep roots, tolerance of poor soils, and efficient dispersal mechanism (small mammals and birds eat the berries, spreading them far and wide) makes white mulberry a terrific invader. White mulberry can be particularly difficult to eradicate once established. If cut down, stumps can sprout and grow vigorously into a new tree. It can form dense stands that exclude other plants. One of the main recognized threats of white mulberry is to the native red mulberry (Morus rubra), found throughout the eastern hardwood forest. The species are weakly differentiated genetically and ecologically, and are highly interfertile. Therefore, the non-native is a direct and successful competitor for space, and is gradually replacing the native with hybrids- white mulberry and hybrids may now outnumber the native red mulberry!
Distinguishing the two species is difficult, but guides with excellent pictures of buds, bark and leaves can help. One way you can control this invader is to make sure that your next nursery purchase is a native red mulberry rather than its invasive relative (and request that your nursery promote indigenous species in general). Also, inquire with your local, state, or regional authorities to see if parks and roadsides are landscaped with natives.
If you are able to identify the white mulberries in your neighborhood or local woodlot, you can help limit reproductive success through delicious harvest! Stay tuned for our tips on white mulberry harvest and preparation.