What is an Arboretum?

The Morton Arboretum has been the champion of trees since it was founded in Lisle, Illinois in 1922 by Joy Morton, president and founder of Morton Salt. The Arboretum encourages the planting and conservation of trees and other plants for a greener, healthier, and more beautiful world. Like other arboreta, it collects, studies, grows, shares knowledge about, and ultimately protects trees.

The inspiration for the Arboretum had its origins in Morton’s own family tree. His father, J. Sterling Morton (1832–1902), was the founder of the original Arbor Day in America. The founding documents require the Arboretum to maintain living collections, a research library, and an herbarium—all of which continue to be important parts of the mission.

Living collections at an arboretum can be defined as trees that are grown with a purpose. Scientists and researchers can study these trees, learn how they grow, and understand what it takes to keep them safe and healthy. Further, these collections of trees can serve as stored genetic diversity.

The Morton Arboretum’s curator and head of collections hunted plants throughout the southern United States, collecting acorns from oak species such as the endangered Oglethorpe oak (Quercus oglethorpensis), the endangered Georgia oak (Quercus georgiana), Boynton sand post oak (Quercus boyntonii), and Arkansas oak (Quercus arkansana). The material he collected will be shared with gardens and arboreta to increase the genetic diversity of their oaks.

Researchers also collect herbarium specimens during their time in the field.

Herbarium specimens are plants that have been pressed, dried, identified, and accessioned into a museum collection. Each preserved specimen is labeled with information about where and when it was collected. These specimens capture unique information about species ecology and form. As libraries of biodiversity, herbaria are essential to understanding how plant populations and species distributions change over time.

Herbarium specimens serve as a road map back to populations, allowing researchers to revisit the same sites years later to see if those trees are still present or if the plant community has changed.

Trees can also be organized by scientific plant groups. This is an effective way to compare related plant species first-hand.

The Morton Arboretum has five champion collections: oak (Quercus), elm (Ulmus), maple (Acer), magnolia (Magnolia), and crabapple (Malus). Trees in these collections are curated, or chosen, by experts. These collections have high conservation value because they include genetic diversity and are supported by detailed record-keeping.

At The Morton Arboretum, there are nearly 200 trees in the oak collection that represent species from around the world. Why would an arboretum curate an oak collection? Oaks are culturally, economically, and ecologically important trees, and they need conservation help.

There are approximately 450 species of oaks in the world. They can be found across the Americas, Asia, and Europe. Oak trees are majestic beauties and symbols of strength in many cultures. The oak is the national tree of not only the United States, but of England and Germany as well.

DNA can be extracted from herbarium or living specimens and used to answer important questions about biodiversity and the evolution of form and function in trees.
Analyzing DNA can help arboreta with plant breeding and improvement, population management policies, and conservation decisions.

Genetic techniques have been used to improve conservation efforts for the paper-barked maple (Acer griseum). This tree is endangered in the wild in China because its populations have been fragmented and often produce seeds that cannot grow.

Working with scientists from all over the world, researchers from The Morton Arboretum collected samples to assess the genetic diversity in paper-barked maple trees that live in arboreta and gardens, as well as in the wild. Scientists can use this information to identify populations of paper-barked maple that harbor the most genetic diversity.

Root biology is a key area of tree science. Roots are important for the health and stability of trees: they take in water and they anchor the tree to the ground.

Since roots can grow 18 inches per year in the midwest climate, trees have to be planted in areas that can accommodate their root structure. Restricted urban environments can be detrimental for the health of trees. By studying roots, arboreta can help cities more effectively choose and maintain trees.

George Ware (1924-2010) was hired at The Morton Arboretum in 1968; his research focused on urban tree breeding and improvement. At this time Dutch elm disease, caused by a fungus from Asia, was devastating the most commonly planted street tree in American cities. Ware saw the potential in Asian elms and began hybridizing and breeding trees that were resistant to Dutch elm disease and could thrive in urban conditions.

The Morton Arboretum introduced Ware’s cultivar ACCOLADE® elm (Ulmus davidiana var. japonica 'Morton') to the world. This beautiful tree, which is an Asian hybrid, demonstrates good resistance to Dutch elm disease, elm yellows, and elm leaf beetle.

The Morton Arboretum continues to breed new species that will succeed despite urban challenges like compacted soil, pollution, and restricted growing sites. The Arboretum partners with the Chicago Botanic Gardens and the Ornamental Growers Association of Northern Illinois in the Chicagoland Grows® Plant Introduction Program to bring to market new trees and shrubs that thrive in difficult local environments.

Formal partnerships around the world strengthen tree conservation efforts in gardens and in the wild, assess genetic diversity of threatened tree species, and develop programs that support tree conservation education.

For example, The Morton Arboretum is a champion of oaks, and collaborates worldwide to save this genus.

Some arboreta have joined together to collaborate and network via ArbNet, an arboretum accreditation program. ArbNet was developed by The Morton Arboretum to establish and share a widely recognized set of industry standards to unify the arboretum community, provide benchmarking, and share guidelines for professional development.

The ArbNet accreditation program recognizes arboreta at various levels of development, capacity, and professionalism. Registered institutions range from small, local cemeteries to large, established public gardens—all working to advance the planting and conservation of trees.