What's Killing Old Trees?

We live in a period of rapid environmental change. Glaciers and polar ice are shrinking at a record-breaking pace. Polar bears, elephants and tigers are threatened species. It’s not surprising, then, that the world’s oldest living beings—our magnificent, stately trees—are also dying at an unprecedented pace. ‡

What’s happening to old trees?

Old trees, between 100 and 300 years old, are dying at an alarming rate. Researchers from Australia and the US published their findings in the journal Science in 2012. Lead author Professor David Lindenmayer of the Australian National University said they first suspected something was happening while studying Swedish forestry records going back as far as the 1860s.

A 30-year Australian study of mountain ash (Eucalyptus regnans) trees also piqued their interest when it revealed that even in years when trees weren’t destroyed by bushfires, they were dying at 10 times the normal rate.

As the researchers expanded the scope of their study, they found that the increase in tree deaths was happening around the world. Old trees are dying on the African savannah, in the Brazilian rainforests, in Europe’s temperate forests and in our own bush. Trees are also dying in agricultural settings and in cities.

Old trees are the largest living organisms on Earth. The oldest known tree is a 9550-year-old spruce tree discovered in Sweden in 2008. Researchers were able to determine that four generations of trees in that area shared the same genetic material.

The trees are able to create cloned copies of themselves through the growth of their root penetrating branches, an ability that allows them to grow a new trunk when the old one dies. This has enabled these ancient trees to survive.

The root of the problem

Climate change is one of the largest threats to the survival of trees, as warmer temperatures contribute to

• bushfires
• insect infestations
• drought

Other threats to old trees include

• land clearing
• agricultural practices
• logging practices
• increased carbon dioxide levels

Young trees are dying, too

Recently, forest ecologists made a surprising discovery: older forests may be able to stand up to climate change better than younger forests.

While studying forests in Alberta and Saskatchewan, Canadian researchers found that different tree species respond differently to climate change. Prior to the study, they assumed that all trees were affected equally by climate change. But it turns out that the species hit hardest are those that require more water, such as poplar and balsam. Drought-resistant species are better able to adapt to climate change.

Trees with benefits

The secondary effects of climate change affect trees whether they’re young or old. But trees also positively affect us every day in ways that we may take for granted.

Room and board

Trees have an immense ecological impact. They are estimated to provide homes to 30 per cent of all birds and animals in particular ecosystems. They also provide food: fruit, nuts and seeds.

Lindenmayer’s co-researcher, Professor Bill Laurance of James Cook University, explains the significance of big trees: “Their hollows offer nests and shelter for birds and animals like Australia’s endangered Leadbeater’s possum—and their loss could mean extinction for such creatures.”

Even dead trees are used as lookout spots for birds, and stumps provide homes for many animals and insects. By doing this, trees help to promote biodiversity.

Air care

The amount of carbon dioxide a tree can remove from the air depends on its size. In a year, a tree may remove as much carbon dioxide as a car creates driving 41,600 kilometres, while a 40-year-old tree may have removed one tonne of carbon dioxide from the air over its lifetime. Trees release oxygen, and their leaves evaporate water from the air, lowering air temperature and keeping us cool, as well as shading us under their leafy canopies.

Heat reduction

Trees in urban areas help reduce the “heat island effect.” Large areas of paved bitumen and concrete absorb and reflect heat from the sun, increasing temperatures and contributing to global warming. Leafy trees can help mitigate this effect by providing shade.

Soil quality and stability

When the many components of trees break down—leaves, needles and branches—the broken-down organic matter not only nourishes tree growth, but it also enriches the quality of the soil. In watershed areas, trees can help prevent flooding by taking in large amounts of water through their roots. Roots also filter contaminants to help prevent their release into rivers, lakes and other groundwater sources.

Functional beauty

Aside from their environmental benefits, trees have many practical uses. They can provide privacy, reduce noise, block wind, frame a pleasant view or block an unpleasant view and provide beauty in backyards, parks and urban centres.

Human health

A recent US study looked at the effects that dying trees have on human health. Researchers examined data from 15 states between 1990 and 2007 to determine the health effects of infestations of the emerald ash borer, a beetle that has destroyed more than 100 million ash trees in the eastern and midwestern US.

They found 15,080 more cardiovascular-related deaths and 6113 more deaths from lower respiratory disease in beetle-infested areas compared to non-infested areas. The results were consistent when demographic differences such as race, education and income were taken into account, although the association was strongest in areas of above-average household income.

Proper protection

Ecologists who study trees are calling for further research to determine the extent of loss of old trees and to figure out where these trees have the best chance for survival. If we lose old trees, we will lose the ecosystems they support and the many environmental—and health—benefits they provide.

Laws and regulations that protect old trees vary across Australia. Trees may be protected by legislation three ways:

• local government bylaws
• state and territory legislation
• federal legislation

Local government councils and shires may have bylaws, registers or lists, “overlays,” local laws or local planning instruments that protect trees. Other laws may protect trees through heritage and/or Indigenous heritage legislation, administered by state-based statutory authorities.

Legislation varies in consistency and effectiveness. Only the Australian Capital Territory and South Australia have specific statutes to provide protection to native and non-native tree species on private land; the Northern Territory, on the other hand, has no laws to protect trees on private land (unless the trees have separate heritage listings).

Trees in our National Parks receive the highest level of protection, and penalties enforced by park rangers are significant; all states and territories have parks laws. The Environment Protection and Biodiversity Conservation Act 1999 is the Australian Government’s central environmental legislation, offering additional protection for heritage listings and species considered threatened, endangered or vulnerable. Check out registers of significant trees held by many councils and municipalities to help conserve our urban forests.

Medicinal trees

Trees have a long history of providing natural medicinal remedies.

Save our forests

Learn more about how to protect our endangered old-growth forests and about the effects of climate change on trees at

• Australian Conservation Foundation (acfonline.org.au)
• Australian Forests and Climate Alliance (forestsandclimate.org.au)
• Greenpeace (greenpeace.org.au)
• National Trust (nationaltrust.org.au)
• Friends of the Earth (foe.org.au)
• UNESCO World Heritage listings (whc.unesco.org)