Ancient dawn redwood survives wet weather
With heavy rains and occasional flooding continuing through several seasons across the Midwest, extended inundation may spell the demise of many evergreen trees in cities. If flooding occurs during winter, most deciduous trees will survive because they are dormant and do not need to obtain oxygen from their roots at this time. Typical riverbank species such as cottonwood and willow are naturally adapted to flooding, whether leafed out or dormant. When floodwaters recede, landscapes in cities, towns and neighborhoods reveal the extent of the damage to landscape trees.
There is a single tree that will provide the optimal replacement species for these areas. It provides a great opportunity to replant boulevards, parks and yards with Metasequoia glyptostroboides, the dawn redwood of China. Closely related to two California natives, coast redwood (Sequoia sempervirens) and giant redwood (Sequoiadendron giganteum), this third genera of the redwood clan is the only one that’s deciduous. Thus, winter flooding may damage its cousins, but dawn redwood adapted to unseasonable flooding a million years ago.
It thrives in both dry ground and in standing water, proving it is superadapted to soils and conditions often subject to flooding. In many ways, this tree blends the appearance of California redwoods with inundation tolerance of another relative, the deciduous swamp-dwelling bald cypress (Taxodium distichum).
Dawn redwood is a very new tree in horticultural terms. In 1941, the first Cretaceous Period fossils of the species were discovered, then just three years later, actual living trees were found on the verge of extinction in Hebei Province in southwest China. In habitat it is known as shan shui, water fir, attesting to its tolerance of soggy ground.
Paleobotanists believe these few trees were the remnants of much larger forests that died out long ago as ice ages forced them farther south to warmer regions. The Hebei trees became the genesis of the world’s cultivated Metasequoia population, so the gene pool is limited. When we plant this amazing tree, we become a part of the worldwide effort of ex-situ conservation, which is the act of planting threatened trees in landscaping to protect them from extinction.
From studies of the first plantings of Metasequoia in China as street trees, we have learned much about its curious needs. It is lauded among the very best urban landscape trees, adapted to pollution, a high water table and dangerously acidic soils.
Foliage of the dawn redwood is soft, feathery and bright green, with some trees verging on gold. They develop orange coloring before leaves drop in the fall. At maturity they reach 50 to 90 feet tall, with a very pyramidal form, but after a half-century they become more spreading. Roots prefer acidic soils around pH 4.5, which is a problem solver for areas of high rainfall such as the Pacific Northwest. It is technically hardy to USDA Climate zone 4, but the wild stands’ habitat is classified a warm zone 9. Such ancient genetics may be why they are thriving in Quebec, where acid rain and cold winter actually create ideal conditions for growth.
When a tree solves many problems like this one can, it makes an excellent residential landscape specimen that suffers no known pests or diseases. They are sold by most garden centers and are best purchased in larger container sizes, often by special order. They prefer to grow as a single individual because it resents crowding of other trees and plants, perhaps because it is very jealous of its sunlight and will not perform in light shade. This redwood prefers its canopy in full sun and its root zone in cooler ground, so mulch generously in the summer.
When climates change and the impact of weather disasters demand we replant city, park and boulevard trees after flooding, think outside the box. When we can choose a tree that withstood the evolution of the Earth for millions of years, it deserves more attention. If it could speak, just imagine what Metasequoia would say about changes caused by epic volcanoes, meteor strikes and continent-sized glaciers that make our current weather variations look like just a drop in the bucket.