T e a c h e r  C r e a t e d  L e s s o n

Using our Forests Wisely

mmcdermid

Educator, Richmond, British Columbia

Forests as a source of Carbon Dioxide



Trees produce their own food and contribute to the ecosystem.

British Columbia Forest Discovery Centre
c. 2000
British Columbia, CANADA

© 2006, British Columbia Forest Discovery Centre. All Rights Reserved.

Transcript

Clever students will remember that plants are the only organism that can make their own food. All other forms of life, animals and fungi and microbes all depend on the food that is produced by plants. Trees are plants. So trees can produce their own food as well. They go through a process called photosynthesis by which they pull carbon dioxide out of the air and they combine it with water and sunlight to make sugars, which are stored in the tree and shared through it’s roots to other organism around the roots. They are generally used to build the mass of the tress. The tree in growing, in building wood and foliage and other tissues is pulling carbon dioxide out of the air, and it is using it to make tree tissues. Trees, in particular, are important because of their size and because we live in a forested province, these trees are pulling carbon from the air and using it to produce tree tissue. The trees in the forests and all the plants, though primarily the trees, are an important store of carbon – a mature forest has a whole bunch of carbon tied up in wood – in the tissue of the trees. If you go in and remove the trees from the site, you remove all the carbon stores from the site. So that greatly affects the amount of carbon that remains in the ecosystem. If you regenerate it through younger trees, which is what we do with sites that are logged in British Columbia, then these younger trees will then commence to pull carbon dioxide out of the air and use it to build their tree bodies. In fact, a lot of these younger trees will be able to remove carbon from the air more quickly then some of the older forests. However, that doesn’t mean there is a net carbon gain from logging old growth forests and replacing them with young forests. In general, there is so much carbon that is stored in dead material, in the older forests, than the standing trees, that the effect of logging these old growth forests and replacing them with younger forests often leads to a net release of carbon into the atmosphere. It is a very complicated issue, there is a lot of debate about it. You will be able to find websites that argue it both ways. A lot of it has to do with what they do with the carbon they remove from the site. You can imagine the site is logged, people cut the trees down and take them to a mill and make them into lumber. The lumber is then taken and used to build a house, build a school, something like that. That carbon that is in the wood will probably remain as 2 by 4’s in the walls of the house or the school for decades. Perhaps for a century. So, the carbon isn’t released back into the atmosphere anytime soon. If, on the other hand, the wood that is removed from the site is used to make pulp and paper, or something like tissue paper or toilet paper, it can find itself back in the atmosphere again within a year. One of the effects that is difficult to model in trying to figure out where all the carbon is going, is just what the products that are removed from the forests, the tree trunks, are used to make. And that is a really important determent in how long it takes the carbon to get back into the atmosphere and that’s important from a global carbon cycling point of view.