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. 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 trees also piqued their interest when it revealed that even in years when trees weren’t destroyed by wildfires, 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 northern boreal forests. 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 9,550-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

• forest fires
• 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, Canadian 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, 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, such as the Jack pine, are better able to adapt to climate change.

According to Han Chen, a professor in the Faculty of Natural Resources Management at Lakehead University in Thunder Bay, Ontario, 20 percent of Canadian forests are considered old (with an average tree age of more than 80 years). That leaves 80 percent of our forests made up of younger trees (less than 80 years old).

Chen says that forest fires are estimated to occur once every 50 years in a given forest. The first trees that grow back after a forest fire are species such as aspen and Jack pine. The trees that grow back later, such as black spruce and white spruce, are more sensitive to the warmer, drier conditions created by climate change than aspen and Jack pine.

If younger trees are more vulnerable to climate change, Chen says, our current predictions may vastly underestimate the effect of climate change on the trees of our boreal forests.

Another threat: the mountain pine beetle

Warmer temperatures have had other effects on Canada’s boreal forests. Although the Jack pine may be more resistant to drought than other species, it has another, bigger problem: the mountain pine beetle. The pine beetle has destroyed 50 percent of the commercial lodgepole pines in BC, and is now inhabiting, and destroying, the Jack pine. Warmer summers and milder winters have enabled the beetle to survive, as rising winter temperatures mean that the weather is not cold enough to kill it.

The pine beetle’s ability to fly more than 100 kilometres to colonize new forests has increased its territory from BC to Alberta and Saskatchewan, with expectations for it to continue its relentless devastation of these pine species across Canada. So far, affected provinces’ pest management strategies have included removing and burning affected trees, and harvesting damaged trees while their wood is still a usable commercial commodity.

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 percent of all birds and animals in particular ecosystems. They also provide food—fruit, nuts, and seeds. Even dead trees are used as lookout spots for birds, and stumps provide homes for moles, salamanders, 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 asphalt 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 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

Besides 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. The emerald ash borer is a beetle that has destroyed more than 100 million ash trees in the eastern and midwestern US. When researchers examined data from 15 states between 1990 and 2007, they found 15,080 more cardiovascular-related deaths and 6,113 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.

Policies that protect old trees vary across Canada. Trees may be protected by legislation three ways:

• municipal bylaws
• provincial legislation
• federal legislation

Local municipalities may have bylaws that protect trees and/or designate them as a heritage site. Provincial legislation varies in effectiveness. In Ontario, for example, old trees may receive heritage designation and protection under the Ontario Heritage Act, while 600,000 hectares of old-growth forest on BC’s Vancouver Island and South Coast are not protected by provincial legislation. According to the Sierra Club’s report, Carbon at Risk: BC’s Unprotected Old-Growth Rainforest, this area stores more than 225 million tonnes of carbon, the equivalent of  more than 13 times the province’s annual emissions.

Heritage trees deemed to be “federally significant” may be designated a National Historic Site by Parks Canada. Individuals or groups may apply for designation. Algonquin Provincial Park, in Ontario, is an example of a National Historic Site of Canada. One of its founding purposes was to create a forest reservation where issues of forest conservation versus recreational use, and forest preservation versus logging, could be explored.

Check out local programs at municipal or city parks to learn about trees and help conserve our forests.

Save our forests

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

• Tree Canada treecanada.ca
• Ancient Forest Alliance British Columbia ancientforestalliance.org
• Sierra Club sierraclub.ca

Medicinal trees

Trees have a long history of providing natural medicinal remedies.