Can You Imagine a World Without Trees?

The Morton Arboretum

Trees are the cornerstone of Earth's ecosystems.
They provide habitat for animals and other plants. And people need them. Despite their critical importance to people and ecosystems, at least 10 percent of the world’s roughly 100,000 tree species are threatened with extinction.

Trees make our lives better in ways we may not notice. They clean air, store carbon, and provide food, timber, fuel, and medicine. Scientists call these benefits ecosystem services. Humans would have to pay billions of dollars for these ecosystem services if we let our trees die.

Trees are increasingly vulnerable in a changing world.
Trees grow slowly. It can take decades for them to reach maturity and reproduce. For example, it can take 150 years for a white oak (Quercus alba) to grow from 20 feet to its mature height at 60 feet tall. And, unlike animals, trees can’t move when their habitat becomes inhospitable. Since trees stay where they are planted and many trees have seeds that are not easily dispersed, they are often trapped in a rapidly changing environment.

Tree conservation means that we are trying to make sure trees will be around for future generations. A tree simply surviving does not mean it has been conserved. Trees need to be able to pass their genes on to the next generation. Experts consider a tree successful if it survives, grows, and reproduces.

Arboreta are leaders in tree conservation.
Arboreta are botanical gardens specializing in trees; they can be described as outdoor living tree museums. They practice scientific research, promote conservation, and engage in public outreach and education.

The Morton Arboretum, for example, is a champion of oaks. Oaks are culturally, economically, and ecologically important trees, and they need conservation help. The Arboretum is collaborating with researchers around the globe to study and protect oaks in all of their different habitats.

One way arboreta help conserve tree species is by collaborating with other gardens through collecting trips and joint initiatives. Not only do arboreta share seeds and living specimens, but they share research, knowledge, and skills to make sure trees will be around for future generations.

The dawn redwood (Metasequoia glyptostroboides) is a Chinese relative of the giant redwoods and sequoias from California. This tree is endangered in the wild due to overharvesting and habitat destruction. It takes a long time for this species to reproduce. However, several botanic gardens around the world, including The Morton Arboretum, are cultivating this species to maintain the gene pool and keep the dawn redwood from becoming extinct.

Working together, researchers have identified many threats to trees, including overharvesting by humans, pests and diseases, climate change, adverse urban conditions, and decreasing diversity. Let’s look at some examples and how arboreta are responding to them.

Climate change
Some trees are no longer adapted to where they once grew. Because of climate change, habitat is shifting, often moving north or up in elevation. Climate change also causes unpredictable weather patterns. Some habitats are becoming unusually dry; others are becoming too wet. These dramatically changing conditions leave trees more vulnerable to pests and diseases which are free to move into new regions. In addition, more droughts can increase the intensity of forest fires, which releases carbon into the atmosphere, which further increases the impact of climate change.

An example of how climate change can impact a species' range is the yellow birch (Betula alleghaniensis; previously Betula lutea). This large tree is relatively common throughout New England and southern Canada. It produces valuable lumber and is an important food source for many animals. In Illinois, however, yellow birch is becoming very rare as climate change warms this region and shifts the range of this tree further north.

While there is no solution to climate change, arboreta document the observable changes in trees and their habitats. They analyze and share the results of their research in order to advocate for effective responses to climate change.

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.

Herbarium specimens serve as a road map back to populations, allowing researchers to examine species ranges in the past and predict how climate change will affect them in the future.

People sometimes overharvest trees because they provide such important products. Overharvesting, taken to its extreme, can wipe out entire naturally occurring populations. Among the trees at risk for overharvesting are mahogany, agarwood, and sandalwood. In addition to acting as a “life raft” for threatened trees, arboreta build awareness about overharvesting by educating business, policymakers, and the general public. The Morton Arboretum developed an exhibition titled Vanishing Acts that has toured several continents to highlight trees in danger.

The medicinal magnolia tree (Magnolia officinalis) is native to high-elevation forests in the mountains of China. This highly aromatic tree has a thick brown bark that is used as a traditional Chinese medicine to treat chest congestion and phlegm.

Years of overharvesting and habitat destruction threaten this tree in its native China. Efforts are underway to increase public awareness and teach sustainable methods of harvesting medicinal magnolia bark.

Koyama's spruce (Picea koyamae) is a rare and valuable conifer native to isolated locations in Japan. Just a few hundred individual trees remain in the wild. This species is critically endangered because it is outcompeted by other tree species planted nearby for timber. When Koyama's spruce trees are lost due to logging, fire, or typhoons, trees of other species move in to replace this endangered spruce. Because the population is so small and fragmented, this species can’t reproduce and increase its genetic diversity in the wild.

Arboreta are preserving Koyama’s spruce in living collections which will allow experts to continue their research.

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

Even if a tree species is commonly planted, it still needs to be conserved. Ginkgo (Ginkgo biloba) is one of the most commonly cultivated trees, thriving in urban environments around the world due to its wide adaptability. Nonetheless, ginkgo is endangered in its native range in China because it is slow growing, slow to reproduce, and overharvested, and its habitat is being destroyed by human activity. The ginkgo's genetic diversity needs to be preserved in its native range to protect this tree's full genetic spectrum for future generations. Until we know that wild ginkgos will survive, arboreta must continue to collect and study them.

Pests like aphids, beetles, borers, and moths threaten trees across the globe. Their impact can be devastating as they enter new regions. Some of these pests arrive by hitching rides in shipping pallets; others migrate due to climate change. How does climate change increase the impact of pests? First, the insects can live in areas that were once inhospitable to them. Second, trees in changing climates have had a chance to develop natural defenses for native pests but not for newly introduced ones.

At The Morton Arboretum, scientists and breeders like George Ware have been breeding pest and disease-resistant trees. Ware was hired in 1968, and 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. He began hybridizing and breeding trees that were resistant to Dutch elm diseases and tolerant of urban conditions. The Morton Arboretum introduced the cultivar ACCOLADE® elm (Ulmus davidiana var. japonica 'Morton') to the world. This beautiful tree, which is an Asian hybrid, has good resistance to Dutch elm disease, elm yellows, and elm leaf beetle.

Urban conditions
With compacted soil, restricted growth areas, and pollution, urban environments are challenging for trees. Research has identified species that can thrive in urban environments and techniques to ensure their survival. Arboreta share this information with city planners and other decision makers so they can choose appropriate trees. The long-term health of these trees benefits everyone in the community.

Specialized scientists study the way trees can fail in urban environments. They publish articles on their findings and make recommendations for best practices so that people who care for trees can be successful. One of these best practices is to increase tree species diversity.

Tree diversity provides protection and resilience. In urban environments, mindful managing of diversity brings many advantages. For example, diseases and pests typically attack a single species. When we plant one type of tree to the exclusion of others, diseases and pests spread more rapidly and have a bigger impact. Healthy ecosystems with a lot of diversity are resistant to future invasions and more adaptive to a changing climate. Increased diversity of trees also provides a wider variety of food and shelter for wildlife.

Overharvesting, pests, diseases, climate change, adverse urban conditions, and decreasing diversity--the list of threats may seem overwhelming, but arboreta are making great progress in addressing each one. Scientists, conservationists, and other advocates are working on the behalf of trees. You, too, can be a champion of trees by supporting this important work.

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