The forgotten forest product

When you hear the words “forest product” what comes to mind? Most of us think of lumber, pulp and paper. If pushed, we might come up with edible forest products like wild mushrooms and maple syrup. But there is another forest product that most of us don’t often think of. And arguably it’s the most important – water.

According to Natural Resources Canada, two-thirds of Canadians get their drinking water from surface waters, including rivers, lakes and reservoirs. Most of the water in those sources comes from forest ecosystems. Forests are also the source of fresh water for many people in the United States. Above: An Ottawa Valley forest soaking up precipitation. Photo Ottawa Valley Tourist Association (source)

So how do forests provide water?

Forest canopies intercept much of the precipitation that falls over them. This rain and snow would otherwise fall directly on the soil, washing it away as erosion. The water that lands in the forest canopy gently drips to the ground with much less force than direct rainfall, and then percolates through the soil into groundwater reservoirs.

In this way, forests act like giant sponges. They collect and store enormous amounts of rainfall. Forest soils absorb four times as much rainfall as soils covered by grass, and eighteen times more rainfall than bare ground. Trees then tap this constant underground reservoir of water slowly and evenly, helping to prevent seasonal floods and droughts.

Trees pull the stored water up through their extensive root systems to use in photosynthesis and other processes such as transpiration. During transpiration trees give off water vapour from their leaves, cooling the tree and the surrounding area. Trees can therefore be likened to “living water fountains” that redistribute water that would otherwise remain underground. 

The water released from tree leaves rises into the atmosphere, then condenses into clouds and falls as rain once again. Biological particles released from forest canopies serve to trigger condensation and rain formation. Without trees to redistribute water and seed clouds, the climate in many areas would be far drier. 

A built-in water purifier

Forests also filter and clean water. Microorganisms and fungi in forest soils filter out substances such as mercury, pesticides and other pollutants, providing clean drinking water for millions of Canadians. Mature forests do this work best and should be protected for this reason.

As our climate changes, due to land surface changes and greenhouse gas accumulation, water shortages are increasing worldwide. Ground water sources are being depleted and precipitation is declining in many areas. Rivers are going dry and lakes are disappearing in some parts of the world. At the same time, world forest cover is also declining at a time when we need it more than ever. Unfortunately, our economic system does not yet recognize or value the water provided by mature forests, putting this vital life support service at risk.

We are forest-rich in the Ottawa River watershed. Three-quarters of the 146,000 square kilometer area of our watershed is forested. Our forests give us wood products, paper, wild food, climate moderation, flood control, clean air, beautiful places for a “nature fix” and many other things. But most important of all of these is water.

About the author: Lynn Jones is a founding member of the Ottawa River Institute, a non-profit, charitable organization based in the Ottawa Valley. ORI’s mission is to foster sustainable communities and ecological integrity in the Ottawa River watershed.

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