Protect Tree Health By Planting For Diversity

By Nancy Buley

Whether in the wild or growing in managed landscapes, trees and the people who care for them are facing unprecedented challenges. A warming climate and changes in historic weather patterns are putting extraordinary pressure on our forests worldwide.

Compromised by extremes in precipitation (flooding/drought) as well as temperature (too hot/too cold), our native and urban forests are increasingly falling victim to pests and diseases that can weaken and/or outright kill once-healthy trees.

Urban foresters tell us that the best defense against climate change, pests and diseases is diversity. Planting a diverse mix of genus and species, adapted to your climate and growing conditions, is key to developing a resilient landscape. By planting a variety of tough, widely adaptable, resilient trees, you’ll greatly decrease the risk of a pest or disease sweeping through the landscapes you manage and causing widespread damage or death of your trees.

To help you get started on the path to selecting and growing healthy, durable trees that will enhance your landscapes large and small, we recommend these tough, adaptable, pest and disease resistant, climate-forward trees. Classic shade trees with broad canopies, columnar oaks, and trees of small stature are described.

Flashfire® Maple

(Acer saccharum ‘JFS-Caddo2’)

Named for its brilliant orange-red fall color, Flashfire® Maple is our top pick among trees grown from seed collected from an isolated population of sugar maples located in Caddo County, OK. This strain of heat-adapted sugar maples has evolved in rocky, arid, limestone soils of western Oklahoma. This heritage makes it a good fit for difficult urban planting sites. Flashfire® Maple is well adapted to hot and dry weather, but still has good cold hardiness. Its leathery dark green leaves are tolerant of heat and drought and resist leaf tatter. Fall color develops at a younger age than most sugar maples and is a reliable, brilliant red. ‘John Pair’ and ‘Autumn Splendor’ are cultivars selected by the late Dr. John Pair for whom the John C. Pair Center of Kansas State University is named. Powder Keg® Maple (Acer saccharum ‘Whit XLIX’ PP 23957) is also descended from the Caddo maple population. Hardiness is USDA Zone 5.

White Shield Osage Orange

(Maclura pomifera ‘White Shield’)

What’s not to like about this handsome, durable shade tree? It thrives in urban soil conditions ranging from acid to alkaline, wet to dry, and is tolerant of drought, periodic flooding and road salt. Fruitless and thornless, its strong wood and branch attachments prevent storm damage. Resistant to diseases, insect pests and deer, the tree is a fine choice for sites where other trees fail.

Wichita Osage Orange is another fruitless option, developed by the late Dr. John Pair of Kansas State University. It presents a more symmetrical and fully branched canopy as it reaches a mature height and spread of 35′ x 35′. It also lacks the spiny thorns typical of seedling-grown trees.

Though its native range is limited mostly to Arkansas, Oklahoma and Texas, Osage Orange is widely adaptable and thrives throughout much of the Midwest and beyond. Its spread is thanks to early settlers who planted thorny seedlings to grow a hedge or fence row to be “horse high, bull strong and pig tight.”

Espresso™ Kentucky Coffee Tree

(Gymnocladus dioicus ‘Espresso-JFS’)

Arching branches of this North American native tree give it an elm-like form. Huge, doubly compound leaves composed of small, bluish-green leaflets provide filtered shade and give it a tropical feel. Our seedless selection bears none of the big seed pods that can be problematic in landscapes and streetscapes. This long-lived and highly adaptable tree is tolerant of heat, drought, cold and acid to alkaline soils. Mature height and spread are approximately 50′ x 35′.

Swamp White Oak

Swamp White Oak (Quercus bicolor)

Don’t be fooled by its name. While it is well adapted to poorly drained sites, Swamp White Oak handles drought equally well. Though in the wild it is found most often in low lying, moist bottomlands, it is adaptable to a wide range of growing conditions. Its lustrous dark green leaves have wavy margins. Fall color ranges from yellow brown to reddish tones. Its canopy is rounded and open, with a mature height and spread of about 45′. (Zone 4)

American Dream® Oak

(Quercus bicolor ‘JFS-KW12’ P.P. 23632)

This fast-growing cultivar offers the drought and heat resistance of the species, as well as the ability to thrive on poorly drained sites. It also demonstrates good resistance to anthracnose and mildew – diseases often exhibited by seedling-grown trees. Its large, lustrous, deep green leaves are thick and glossy, with wavy margins. After turning buttery yellow in autumn, they turn to rich tawny brown and remain on the tree late into the season.

Texas Red Oak

(Quercus buckleyi) is a native of Texas and Oklahoma that offers bright fall color. Moderate in size for an oak, it grows in about 35 years to a height and spread of approximately 40′ x 40′. Green, glossy summer foliage turns orange red to red in autumn. Dr. Greg McPherson, retired USDA urban forester who led the aforementioned 17-year performance trial, describes it in one of a series of videos about Climate Ready Trees presented by Tree Davis, a non-profit tree planting organization in Davis, California. Prior to his retirement from the Forest Service, Dr. McPherson spearheaded a collaborative 20-year study of climate-ready trees for California, ongoing under the direction of University of California, Davis.

Columnar oaks

For those seeking shade in space-challenged settings, these oak cultivars tailor-made for landscapes that don’t have room for a classic, spreading oak. They offer the same oak adaptability and resilience in a slender package.

Crimson Spire™ Oak

Crimson Spire™ Oak (Quercus bimundorum ‘Crimschmidt’) is a hybrid of the North American native White Oak (Quercus alba) and English Oak (Quercus robur). Introduced by our nursery more than 30 years ago, this hybrid is a tough and time-proven performer in landscapes from California to Colorado, Kansas to Chicago and beyond. Other narrow hybrid cultivars include Streetspire® Oak, Kindred Spirit® Oak, Regal Prince® Oak and Skinny Genes® Oak.

Beacon® Oak (Quercus bicolor ‘Bonnie and Mike’) is a columnar selection of Swamp White Oak (Quercus bicolor) discovered by Dr. Michael Dirr. This slender version of the widely planted North American native offers the same heat and drought tolerance and adaptability to varied climates and growing conditions as the species.

Tough trees of smaller stature

MaacNificent® Maackia

MaacNificent® Maackia (Maackia amurensis ‘JFS-Schichtel1’)

This selection of Amur Maackia is distinguished from seedling-grown trees by its vigorous, upright growth habit and symmetrical, vase-shaped form. Narrow, compound leaves drape from upright branches to give the tree a cool, airy look. Glossy, dark green foliage is complemented by creamy white flowers in mid-summer that are very attractive to pollinators. Blooms are borne on stiff, upright racemes when few other trees are flowering. This attractive small tree (30′ x 22′) performs well in harsh urban environments and has proven tolerant of heat, drought and cold. USDA Zone 3 hardiness and the ability to thrive in poor soils, acid or alkaline, make this nitrogen fixer a great choice for difficult sites.

Seven-son Flower

Seven-Son Flower (Heptacodium miconioides) earned high praise from Dr. Jason Griffin of Kansas State University, who called it the “crape myrtle of the North” in The League of Extraordinary Trees, published in Nursery Management magazine in February 2014. The article recommends “10 species with superpowers that thrived during a historic drought.” It has a lush, tropical appearance in summer, with glossy green leaves that fall in autumn to reveal rugged branches with exfoliating, gray-brown bark. Fragrant while flowers appear in late summer. It’s late-season blooms are a magnet for hummingbirds, bees and other pollinators. After the flower petals drop, the long-lasting ornamental calyxes remain on the plant. They retain their bright red in color well into autumn and are easily mistaken to be the flowers of crape myrtle. Left on its own, it will tend to grow as a large, rangy shrub, but it can be trained to be a single- or multi-stem tree.

Stars & Sparks™ Seven-son Flower (Heptacodium miconioides ‘JFS GM1HM’)

Upright growth habit and stout branch structure form a sturdy tree of small stature that grows to a height and spread of about 18′ x 12′. Unique in form, flower, foliage and bark, this rugged individual is a standout in a species that’s typically multi-stemmed or shrubby in growth habit.

City Sprite® Zelkova

City Sprite® Zelkova (Zelkova serrata ‘JFS-KW1’)

Urban foresters and utility companies already appreciate the compact, tidy growth habit of this petite tree that’s tailor-made for city streets and tight spaces. Short internodes contribute to its compact, dense, and semi-dwarf form, resulting is the perfect little tree for constricted planting sites. Oval to rounded, it grows to a height of approximately 24′ with a spread of about 18′. Fine textured foliage is brighter green in summer than the leaves of typical Zelkova and turns yellow in autumn. Storm-resistant branches and a stout, sturdy trunk assure its survival on city streets.

This small sampler of trees will help kickstart your quest to plant resilient trees for the future. Find detailed descriptions of the trees described in the J. Frank Schmidt & Son Co. online library. For a deeper dive, reach out to your local community’s urban forester or to your state’s Urban & Community forester. You can find a list of State Urban Forestry Coordinators on the Arbor Day Foundation site.

Nancy Buley is Director of Communications for J. Frank Schmidt & Son Co., wholesale tree growers of Boring, Oregon, where she has been “talking trees” for 30 years. A former newspaper reporter, she earned a bachelor’s degree in Technical Journalism and Horticulture from Oregon State University. A Lifetime Honorary member of the American Society of Landscape Architects, Nancy has earned national recognition for her tree advocacy and stewardship efforts including over a decade of service on the board of directors of Friends of Trees. Nancy lives and gardens on a couple of acres in Boring, where in her spare time she helps her son tend an eclectic assortment of trees at their boutique nursery, Treephoria.

Nancy Buley is a previous Turf Magazine featured contributor. Click for one of her previous pieces entitled, “Tree Planting: Evolution Of The Tree”.