Understanding forests, carbon and LCAs

The role of forest carbon in climate change can be confusing. Life cycle analysis is a tool to help better understand some of the relationships.

Forests, trees, carbon and climate change are linked by a large and growing body of science. Forests and trees both consume and emit carbon. Human activities affect forest carbon. The balance is sometimes called a “net carbon balance” and these values change with a wide range of conditions.
 
Human activity also both consumes and emits carbon. Forest industry, forest products and our uses of wood are three sets of important variables, among others, in the net carbon equation. A large quantity of carbon is stored in wood buildings, landfills and other pools.
 
A life cycle analysis (LCA) is an equation or model that incorporates as many variables as possible to determine the net effect of a particular activity on carbon, energy or some other resource of interest. LCAs vary in their focus and purpose.
 
For example, what effect does using wood for energy production have on atmospheric carbon?
 
Burning wood produces more carbon than burning coal. So, does that make coal the more environmentally conscious choice? Probably not. Consider the carbon cycle.
 
The source of carbon must be considered. Coal, petroleum and natural gas are fossil fuels that contain carbon which has not been in living systems for millions of years. Wood contains carbon from within living systems and the carbon cycle. Trees obtain it from the atmosphere. Burning trees returns it to the atmosphere, to be re-absorbed by trees and other plants.

So, does that make wood energy carbon neutral? Not necessarily.

Forests and trees have different LCA outputs based on factors such as forest type, soils, age, stand density and others. Trees and older forests tend to have net carbon balances closer to zero or sometimes even negative. A negative carbon balance would mean a forest would emit more carbon than it absorbs.   So, when older, more mature forests are replaced by regenerating, younger forests, the net carbon balance is likely to be more positive, all other factors equal, which is usually not the case. A graph line showing net carbon balances typically rises and then flattens with forest age.

Carbon pools in the soil, trees and other organisms change with forest conditions. Older forests tend to accumulate increasingly large stocks of carbon. Following a harvest, depending upon the kind of harvest, quantities of carbon are released to the atmosphere, where much of it temporarily resides until it’s re-absorbed by vegetation. Other quantities are converted to wood, paper and energy products. Forest products have variable carbon storage times.

So, a vibrant wood-using industrial sector and research-based forest management will promote more vigorous forests that absorb more carbon, as well as creating semi-permanent pools of carbon in buildings and other end uses. The net effect will likely be a positive carbon balance, which would work against climate change.

Other net effects typically include more robust local economies, more diverse habitat, healthier forests and enhanced ecological services.

However, forest systems and human wood use are complex, involving many variables of unequal importance. Building an LCA model to more precisely describe flows and balances is difficult. Some LCAs quantify only a portion of the entire cradle to grave system. Researchers continually work on improving our understanding of how forests and other ecological systems operate, especially with respect to addressing critical questions about serious issues.

There is no doubt that forests are essential to our survival and that we need them on a daily basis to supply products and services. How we choose to treat valuable natural resources remains a choice.

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