11/06/2013 05:59 EST | Updated 11/06/2013 05:59 EST

Why Do Forests Matter? A Call to Conserve the Last Great Forests

The changes we have seen more recently in our forests have not been caused by plate tectonics or long term climate cycles, but by me, by you, by us. We have converted almost 50 per cent of our planet's forests into croplands, ranches, plantations, subdivisions and highways.

There are few other groups of species that have impacted the face of our planet more than trees. We define the major life zones of earth based on the presence or absence of forests.

At one time all plants were grasses, ferns and horsetails -- green plants that used chlorophyll to capture sunlight and turn it into food and energy. At some point, at some place there was a grand change in the design of plants. While all these ancient green plants had cellulose or wood in the cellular toolbox, there was a change in how it was used, and instead of just using cellulose as an exterior raincoat, it became incorporated into stems.

This new woody structure was accompanied by a complex evolutionary change in internal plumbing that gave these plants the ability to grow tall and maintain that structure.

Stems gave rise to wood, to trunks. This gave rise to the first trees and to forests.

And the world was changed forever.

Our ancient forests came to alter the chemical, physical and biological cycles that drive our planet. These forests became rain-makers, air-conditioners, water reservoirs, chemical recyclers and keepers of biodiversity. They also became major sinks of carbon dioxide. Many of these ancient forests, particularly those that grew in wet areas, held so much carbon that after tens of millions of years of growth and death, the carbon they stored became the reserves of coal, oil and tar sands that we use today.

Over the last hundreds of millions of years, while the amount of tree cover has shifted in many parts of the world in response to plate tectonics and long-term warming and cooling periods, our living planet has continued to be dominated by vast oceans and vast forests.

Historic Global Distribution of Forests (Courtesy World Resources Institute, 1997)

The changes we have seen more recently in our forests have not been caused by plate tectonics or long term climate cycles, but by me, by you, by us. We have converted almost 50 per cent of our planet's forests into croplands, ranches, plantations, subdivisions and highways. For much of the remainder, we have claimed them as working forests to provide us with fuel, timber and fibre.

Indeed our collective global forest wilderness has shrunk to just a handful of places across the planet. The largest are now restricted to the tropical rainforests in the Amazon basin and a swath of boreal forest that extends from Quebec to Alaska, with the largest intact forest remaining on Earth straddling the border of northern Ontario and Manitoba.

As Canadians, it's easy to think that trees are ubiquitous -- the heartland of Canada is a land of trees, rocks and water. But when we look at our country through its trees, what we hold as abundant is actually a rare and dwindling resource. As custodians of our northern forests, we are also custodians of some of the last great forests left on Earth.

Current Global Forest Distribution (Courtesy of World Resources Institute)

The story of forests in southern Ontario is a little different than what we have managed to protect so far in the boreal. In many ways, this reflects a thousand stories of forests around the world.

Here in southern Ontario, starting in about 1800, we experienced more than 100 years of declining forest cover. The rate of this forest clearing was astronomical -- indeed the conversion of the forests in southern Ontario represents one of the largest, wholesale ecosystem conversions our planet has ever witnessed. As woodlands were methodically cleared for farmland and wood was cut to fuel industry and transportation, our forest cover hit a low of less than 10 per cent in the early 1900s. Much of what remained was scrubby second growth, or so heavily grazed by cattle, sheep and pigs that no new trees could grow.

Then what happened in quite extraordinary. As farmers switched from horse and plow to tractors, the ability to farm steep slopes and wet areas decreased, and these hill-slopes and margins began returning to trees. And as industry switched from wood to oil and coal, the demand for fuel from our forests declined.

Historic Changes in Ontario's Forest Cover (Courtesy of Nature Conservancy of Canada, Ontario Biodiversity Council and Ministry of Natural Resources, 2013)

For example, in The Once and Future Great Lakes Country (2013), John Riley writes of the local council of Mono's resolve in 1925, "'to purchase some wastelands being sold for taxes; same to be used for reforestation.'...Erosion was stopped on thousands of acres, and forest now covers more than a third of Mono."

This was a period of new awareness on the value of trees, and the need for forests. After witnessing decades of soil erosion by wind, flooding and rivers that were choked by silt, a new conservation ethic emerged that began to value forests as an important part of the landscape.

As a result, the amount of forest cover in southern Ontario has been slowly increasing for the last century. Unfortunately, we are seeing cracks in this trend. Higher commodity prices are fueling an expansion of farmlands. There is continuing urban sprawl, and an attack on our forests by non-native insects and disease. For the first time in 100 years we are seeing the loss of our forest heritage. The forest recovery that appeared to be happening on its own will now require a more concerted investment if we are to have healthy forests in our future.

In Ontario and in Canada we've been very lucky to have an abundance of forests. This abundance has meant that there is always more. The thing is now, from a global perspective, forests aren't abundant and continue to decline, and there isn't any "more."

Remaining Intact Forests (Courtesy of Canadian Boreal Initiative, 2009)

Here in Canada we still have the opportunity to be an example to the world and protect the best of the last great forests. And fortunately there are groups, such as the Nature Conservancy of Canada and TD Forests, who believe in the importance of protecting these places for the future.

Together, we have an opportunity to protect this natural legacy so that our children and grandchildren can walk under the towering trees of our country's majestic forests.

Written by Dan Kraus, conservation science manager for the Nature Conservancy of Canada in Ontario and contributor to Land Lines (the blog of the Nature Conservancy of Canada).

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