Unit 2 - The Environmental Importance of Forests


Lesson 5: Watershed Protection and Maintenance

When we think about forests and what they provide, water may not be the first thing that comes to mind; however, clean water is one of the most valuable forest products. The cleanest, purest water is water that flows from forested areas. Unfortunately, one third of the world's major watersheds have lost more than 75% of their original forest cover.

In Canada, we are fortunate to have forested watersheds thatprovide much of our water supply. Canada's forested watersheds hold 20% of the world's fresh water.

But what exactly is a watershed?

  • Basically, a watershed is an area of land that drains naturally into a stream or other waterway. Click here to watch a video that explains what a watershed is.

  • The Alberta watershed map, to the right, illustrates the main watersheds in Alberta.

  • Which watershed do you live in?

We have mentioned that the best watersheds are forested watersheds.
But why is this the case?
Read on to discover the reasons.


Image Source: Government of Alberta

To read more about Alberta's watersheds, click here.

When precipitation falls on forested land, it soaks into the sponge—like soil of the forest. As this water slowly makes its ways into streams and rivers, pollutants are naturally filtered out. In addition, very little sediment enters the waterways because the root systems in the forest hold the soil in place preventing erosion.

As a result, the water that is released from a forest is pure and clear. In contrast, water that is collected from non-forested areas, such as farmland or urban centres, often contains pollutants and large amount of sediment.


Forested watersheds regulate water flow by increasing an area's ability to store water. How do forests do this?

  • Forest vegetation occurs in several layers — trees, shrubs, and smaller plants.

  • These layers of vegetation provide a tremendous amount of surface area. This surface area enables the collection of water during storms. Some of this collected precipitation evaporates directly from the surface of the leaves. The rest of the water, however, drips slowly to the forest floor below where it seeps into the porous forest soil. This water may then be absorbed by the roots of plants and trees and returned to the atmosphere through leaf pores. This process is known as transpiration .

  • Water remaining in the soil of the forest will either evaporate directly into the air or flow slowly into streams, rivers, wetlands, and underground reservoirs.

In contrast, deforested areas and urban developments do not store precipitation. Rather, the water from storms quickly runs off into streams and rivers. This often leads to flooding.



Clear cutting leaves no trees to regulate water flow, as shown below.



Think About It!

Your water would need to come from another source until your watershed could be restored.  This would cause great disruption for you, your family, your community and anyone else supported by this watershed.  It would affect wildlife, streams, rivers, lakes, and all life within this watershed.
Healthy watersheds provide critical services, such as clean drinking water, productive fisheries, and outdoor recreation, that support our economies, environment and quality of life.  The health of clean waters is heavily influenced by the condition of their surrounding watersheds, mainly because pollutants can wash off from the land to the water and cause substantial harm.