MFFCD.jpg (22122 bytes)



Home Page
Welcome Page
Table of Contents
Pre-test Information
Tree Basics Section
Environment Section
Recreation Section
Products Section
Balance Section
Internet Links





Environmental Aspects


Wood Energy Curriculum for High School Classrooms


This wood energy curriculum module is divided into five sections.  Each section has a set of exploration topics to help guide students through an aspect of energy, energy use, and the role of woody biomass.  Some materials are provided but, more important, resources are included for development of additional materials. 


1 - Big Energy

2 - Wood Energy

3 - Environmental Aspects

4 - Socio-Economic Aspects

5 - Bringing It All Home


Environmental Aspects of Wood Energy


Using energy has environmental impacts, some of them negative and some, perhaps, positive.  To create useful forms of energy requires the use of energy and, of course, raw materials.  Energy locked in a gallon of oil, or within the cellulose of wood, or that which moves the wind is not useful energy to human beings until a portion of it has been converted into something like gasoline or heat or electricity.  Energy conversion technologies, by definition, will fail to capture some (most in some cases) energy and all have environmental impacts.  More efficient technologies waste less energy.  Impacts on the environment will vary with the technology. 


Comparing the different fuel sources and environmental impacts will involve a complex set of issues.  Looking at the entire process from the very beginning through the end is important.  Comparing different segments of different technologies is like comparing apples and oranges.  A good example involves electricity.  Electric motors are efficient devices, leading a person to think more things should be run on electricity.  However, making electricity has traditionally been a reasonably inexpensive but energy inefficient process, based mostly on the combustion of coal.  The extraction and combustion of coal has significant environmental consequences that are not reflected in the price of electricity.  To look at only the efficiency of electric motors fails to assess the complete picture. 


While the inherent efficiencies of various renewable energy technologies, such as wood energy, are important, perhaps the more important comparison exists against fossil fuels.  We will need to employ every renewable technology in order to displace a significant portion of fossil fuel consumption.  Overall energy efficiencies and strong conservation initiatives will likely be more important over the next couple of decades (longer perhaps) than new technologies. 


This section explores answers to 11 questions.  These eleven questions will likely generate other questions, which would be good to explore.


  1.  What is the carbon cycle?  Why is the carbon cycle relevant?

  2.  How does woody biomass fit into the carbon cycle?

  3.  What is a carbon footprint?

  4.  What is a life cycle analysis?

  5.  How does atmospheric carbon from wood differ from fossil fuel carbon?

  6.  What atmospheric contaminants might come from wood, besides carbon?

  7.  How does that compare with fossil fuel contaminants?

  8.  How does wood compare to agricultural residues?

  9.  What are the potential forest impacts of woody biomass harvesting?  (Nutrients?  Habitat?  Visual quality?)

10.  What is a carbon market?

11.  What is a carbon cap and trade system?



1.  What is the carbon cycle?  Why is the carbon cycle relevant?


Carbon moves through living and non-living pools.  These pools are usually 1) living things, soil & water, and the atmosphere.  The total amount of carbon among the pools changes gradually over time, moving up and down.  The amount of carbon in one pool or another may change more quickly, but the total amount of carbon remains about the same.  The oceans play a huge role in the carbon cycle.  They cover about three-quarters of the planet’s surface and water stores large amounts of carbon. 


Climate scientists are most concerned about the amount of carbon dioxide (and certain other gases) in the atmosphere.  Changes in the atmospheric carbon pool have contributed to climate change over the past 50 years.  Relatively small changes in atmospheric carbon have more global consequences than changes in other carbon pools.  That’s why the level of atmospheric carbon, and the climate effects, has been controversial.  Therefore, much of the climate change science has focused on atmospheric carbon.  However, the entire carbon cycle needs to be considered when talking about climate change. 


Fossil fuels contain large volumes of carbon that get released when the fuels are burned.  Over the past 50 years, large volumes of carbon have been added to the carbon cycle.  The increase in the atmospheric pool has been associated with climate change.  Therefore, the continued use of fossil fuels has been challenged. 


(Click for large image)
Carbon is an element that resides in various "pools" and some of that carbon is mobile.  The increasing amount of carbon in the atmospheric pool has generated large volumes of research about its effect on climate.  The International Panel on Climate Change is a diverse set of scientists that regularly review scientific research and provide reports about what is known and how confident they are about global trends.  The latest report (fifth) dates back to 2007. 

The rising levels of atmospheric carbon is causing an accelerating "global warming" effect.  That effect varies considerably around the globe because of the complexity of climate.  The more obvious and measurable effects are melting ice, rising temperatures, and increased numbers of extreme events.  Other effects are less obvious and uncertain. 

Forests have significant influences on climate.   Younger forests tend to absorb (sequester) carbon at higher rates than older forests.  Of course, the path of carbon from harvested forests must be considered.  However, forest carbon moves back and forth between trees and the atmosphere.  Alternatively, fossil fuel carbon introduces "new" carbon into the cycle, which is an important difference. 

In the diagram, the green arrows represent carbon exchanges among pools of the carbon cycle, usually measured in time frames of days to decades.  The red arrows represent releases of fossil carbon which has been stored for millennia.  It is that carbon which has growing implications on climate change and has, in part, fosters increasing interest in non-fossil sources of energy. 




2.  How does woody biomass fit into the carbon cycle?


Wood is composed largely of carbon and belongs to the pool of living things.  Worldwide, trees and forests contain large amounts of carbon.  As forests are converted to other uses, much of this carbon is released into the atmosphere and soils become exposed to more sun.  This shift from one pool to another can have climate change consequences.  This is one reason why deforestation in some parts of the world has raised concerns among climate scientists.


In North America, deforestation is not occurring.  In fact, our forests have grown in both area and volume, sequestering more carbon each year.  There is also a large volume of carbon stored in wood products, such as houses, as well as in landfills (e.g. paper and cardboard). 


Forests can be managed to increase carbon sequestration.  A more vigorous forest removes carbon from the atmosphere at higher rates than older forests.  Although forests are part of the overall carbon cycle, they can be used to adjust the amount of carbon in the atmosphere, and wood products can serve as a way to store carbon for long periods of time. 


The role of forests, carbon, and climate change is studied by many researchers, universities, and organizations.  In Michigan, the Northern Institute of Applied Carbon Science (NIACS) in Houghton is involved in much of this research. 







3.  What is a carbon footprint? 


How much carbon does your daily activities release in a year?  How much carbon is your school or home responsible for releasing?  How about your town or city?  What about a certain industry, or agriculture? 


The net amount of carbon released is the carbon footprint, not the total amount of carbon.  Many times, an activity both produces and stores carbon.  It’s the difference that matters and is what is considered a “carbon footprint”. 


Another dimension of carbon footprints is the relationship between carbon production and storage over time.  In a short time frame, say a year or so, the net carbon balance may be one thing, but due to long-term effects of some practices, the net carbon balance might be better (or worse) over longer periods of time. 


Timber harvesting might be a good example.  Wood harvested from a forest results in a release of carbon from the soils as decomposition temporarily accelerates.  The fate of the carbon in the trees depends on the forest products the trees are manufactured into.  Solid wood products (e.g. boards, lumber, panels, etc.) will continue to store that carbon for decades.  Paper and paperboard product carbon storage is a matter of years.  However, about 45% of paper products end up in landfills, which stores carbon for long periods.  But, landfills may not be the best way to handle either carbon or waste. 


There are a number of online "carbon calculators" that try to take something complex and reduce it to a single figure.  While the accuracy might vary, it's still interesting to learn how different activities and products compare. 





4.  What is a life cycle analysis?  


During your lifetime, you will collect, store, and release a certain amount of carbon, energy, and many other things.  Calculations that determine your personal carbon balance would be called a life cycle analysis.  This can be done for just carbon or for everything that you might consume and produce. 


These same sorts of calculations can be made for a wide variety of products and groups of similar products.  Automobiles would be a good example.  Or a home appliance.  Or something larger, such as an energy industry. 


As you might imagine, building an equation and populating all the variables with accurate values can be difficult.  And some products or industries are more difficult than others.  A “cradle to grave” analysis, or assessment, is supposed to include everything from the raw material extraction to final disposal of the product. 


Life cycle analyses ought to consider the entire life span of a particular product.  However, sometimes only a portion might be considered.  For example, a sawmill might have a life cycle analysis beginning when the wood is delivered to when the manufactured product leaves the sawmill.  The effects of forest ecology and timber harvesting are not part of the equation.  Nor is the fate of the boards once they leave the sawmill and get made into a tree house.  This is a useful LCA when comparing different sawmill operations, but it does not reflect the total impact from cradle to grave.  So, LCAs can be used in different ways.  Knowing the purpose of a particular LCA is important to appreciate its meaning. 





5.  How does atmospheric carbon from wood differ from fossil fuel carbon? 


It doesn’t.  Carbon is carbon.  However, introducing carbon from sources outside the natural carbon cycle (fossil fuels) creates an imbalance in the cycle.  The degree of this imbalance and the effects of the imbalance are what climate scientists study.  This has much to do with the first two questions in this section. 


So, energy created from wood moves carbon around within the carbon cycle, rather like recycling.  Energy created from fossil fuels introduces carbon that hasn’t been in the natural carbon cycle for millions of years.  It’s this “outside” carbon that makes a difference to the global climate. 



6.  What atmospheric contaminants might come from wood, besides carbon?


There’s a list of gases and other pollutants that can have an effect on the atmosphere; carbon dioxide, methane, nitrous oxide, ozone, and water vapor.  These are collectively called greenhouse gases because they absorb solar energy and re-radiate thermal energy.  This process is fairly well understood but the impacts and consequences remain uncertain, although change is not uncertain. 


These gases don’t have an equal effect on the atmosphere.  For example, methane is a much more serious solar warmer, weight for weight.  However, it comes in much smaller quantities than carbon dioxide.  So, in the end it’s less of problem, but still an important factor.  


Locally, a large wood-using facility will produce noticeable quantities of water vapor, sometimes mistaken for smoke.  With proper emission controls, as would be required under state permit, little smoke smell and few particulates would occur.  The boiler temperature and combustion technology results in few emissions.  This is much different from the common smoky "backyard burner" familiar to many in rural areas. 




Large Combined Heat & Power Plant . . . and a small District Energy plant.



7.  How does that compare with fossil contaminants?


Fossil fuels are not uniform in their emissions.  There are differences between coal, oil, and natural gas.  And there are differences among various grades of coal, oil, and natural gas.  Some fossil fuels are ‘dirtier’ than others, at least in terms of greenhouse gas emissions.  Sources of carbon external to the carbon cycle result in the warming of the atmosphere. 


Some fossil fuels also contain toxic emissions.  Mercury is a commonly cited issue with coal burning utilities.  Mercury levels have increased in many water bodies and in some human food sources, such as certain species of fish in certain lakes and streams.  Arsenic, lead, boron, uranium, sulfur, and other elements can potentially accumulate and cause human health problems.  "Acid rain" can damage certain kinds of lakes and sensitive soils.  Incomplete combustion (which is the norm) produces high levels of particulates, which is like "soot" that can irritate respiratory functions and particularly impact those people with respiratory diseases (e.g. asthma).   The emissions can impact plants, wetlands, water systems, air quality, and other systems.  Much of these emissions could be captured but that technology is expensive and would add a few cents per kilowatt to the consumer. 


Burning of fossil fuels also releases other compounds that can affect human health and/or environmental health, such as benzene, toluene, carbon monoxide, hydrogen sulfide, nitrogen oxides, dusts/particulates, and other trace materials that can have negative impacts.  Think of smog.  Combustion of coal, in particular, also creates quantities of toxic ash which must be properly disposed of.  Wood releases far fewer (or none in some cases) of these emissions.  So, emissions aren't about just greenhouse gases.


Lastly, the extraction processes of fossil fuels can cause long-term environmental damage, such as oil spills, groundwater contamination, mine disasters, and severe habitat alterations (e.g. pronghorn in Wyoming's Powder River Basin).  In parts of the world with fewer environmental regulations, these impacts are often more severe and have global implications.  Fossil fuels do not grow back as they are extracted, unlike trees.  Global supplies of different fossil fuels vary.  Petroleum is the fossil fuel of greatest concern at this time.  The USA currently has large supplies of coal and natural gas. 



8.  How does wood compare to grasses or agricultural residues? 


Spreading wood ash
back onto forest lands.

One of the waste products from any combustion process is ash.  Disposal of ash can be a problem when the ash has certain levels of toxic elements and chemicals.  Ash from wood and agricultural residues can often be spread back onto the landscape (unlike fossil fuel ash).  Disposal is an expense.  Wood has considerably less ash and the difference in disposal costs can become important.  Wood ash also typically has lower levels of toxic elements.


Wood is available year-round, while agricultural products come onto the market only once or twice in a year, and sometimes not when feedstocks are most needed.  Usually wood can be "stored on the stump" but holding harvested agricultural residues requires buildings and air quality controls. 


Once any plant material is harvested, decomposition begins, which results in a loss of energy content.  Roundwood (logs) decomposes more slowly than agricultural residues.  However, wood chips and grindings need to be utilized promptly, depending upon the weather.   


Growing wood, especially in natural forests, offers environmental benefits not typically found in agriculture.  A farm crop often has significant inputs of energy and fertilizer, although post-harvest residues usually do not.  A farm crop is also a monoculture with few other plants.  Even a woody biomass plantation offers more habitat benefits than a farm field, especially during the winter and during breeding/brooding seasons. 



9.  What are the potential forest impacts of woody biomass harvesting? (Nutrients?  Habitat?  Visual quality?)


The harvest of trees, for all wood products, has impacts on nutrient cycles.  Woody biomass harvesting will take more fiber from the forest than what more traditional harvesting removes.  The potential effects on soil productivity have been cited as a possible problem with woody biomass harvesting. 


Forest soil nutrient cycles have been studied for decades.  Increasingly, the effects, over time, of biomass harvesting are being examined.  However, biomass harvesting has not been going on long enough in the United States to directly measure the effects.  However, using models and a fairly good understanding of natural cycles, woody biomass harvesting from most forest types on most forest soils should not result in long-term nutrient deficiencies or losses in soil productivity. 


Many states, including Michigan, have developed woody biomass harvesting guidelines to minimize the chances of negative long-term soil impacts.  Most of the plant nutrients are in the leaves and small branches.  Most of this material is usually left on-site even when woody biomass is collected.  Harvesting during winter (six months or more in Michigan) means the hardwoods have already lost their leaves.  Nutrients have either been stored in the roots or have become part of the forest floor.  Even during the growing season, it is difficult to remove more than 75% of the material on a forest site. 


Habitat considerations associated with woody biomass harvesting usually mean leaving certain woody structures on the harvested site.  Large diameter logs and tree pieces are called coarse woody debris.  This material, especially as it decays, provides important habitat for a range of species.  Large logs of a certain quality become drumming logs for ruffed grouse.  Hollow and rotten standing trees provide dens and cavities for another suite of species.  These ‘snags’ are also roosts for hawks, owls, and other raptors.  The more open, or completely open, habitat following a timber harvest benefits many species.  These temporarily open areas are especially important in heavily forested areas where such habitat is less common. 


The more important negative consequence of woody biomass harvesting, or any timber harvesting, is probably the visual impact.  The visual change (or how it looks) from a well-stocked forest to either a thinner forest or clearcut forest can be unacceptable to some people.  This is a valid consideration and important in social acceptability of timber harvesting, but it also needs to be weighed with all the benefits that come from harvesting.  





10.  What is a carbon market? 


Groups that store carbon or use less carbon can sell that difference on markets, like commodity exchanges.  The markets can be voluntary or they can be the result of government carbon policy.  For example, a forest owner that manages their forest in a way that would sequester more carbon, that amount of carbon can be sold to a company who has agreed to (or been forced to) a certain carbon emissions cap.  If that company produces more carbon than what they claim, they can purchase carbon "savings" from the forest owner.  Typically, exchanges (buying and selling) is done only through members.  Membership involves agreement to a set of goals and practices. 


In this way, wood energy companies can potentially sell carbon that would have been produced through fossil fuel combustion to companies that currently produce too much carbon, perhaps a power company that burns coal.  Voluntary carbon markets in the United States have not done well, financially.  Government policy levers in some European countries have made the carbon market quite lucrative for renewable energy companies.  For some, the carbon sales comprise an important part of their annual income.  Carbon emitters that exceed prescribed limits must either purchase carbon credits or pay fines. 


Government policies that attempt to regulate carbon emissions and create carbon markets are highly controversial.  For a few years, the Chicago Climate Exchange traded carbon among members and many Michigan forest owners received money for agreeing to manage their forests in a certain way.  That exchange is no longer active. 



11.  What is a carbon cap and trade system? 


A cap and trade system is usually government policy designed to reduce greenhouse gas emissions, primarily carbon dioxide.  Companies that produce large amounts of carbon are allowed to emit only a certain amount.  This is the cap.  Other companies, or organizations, produce less carbon than what they are allotted.  So, companies with carbon deficits can sell that deficit to companies that exceed their caps.  Carbon caps can be adjusted to encourage certain energy production technologies (e.g. renewable wood energy) and discourage major polluters (e.g. inefficient coal utilities).  This policy tool sets limits and then lets the free market figure out how to best respond. 


An alternative to a cap and trade market is to have the government force companies to comply with carbon emission limits using technologies prescribed by the government.  This is the model that many of the emission controls have been applied, such as those with sulfur dioxide. 


Both of these government policy models are controversial. 





MSUElogo.tif (16254 bytes) This website was developed and created by Michigan State University Extension for the teachers of the State of Michigan. 

Page Name:  3-EnvAspects.htm