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Peak Soil: Why Biofuels are Not Sustainable and a Threat to America's National Security

By Alice Friedemann

Introduction

Ethanol is an agribusiness get-rich-quick scheme that will bankrupt our topsoil.

Nineteenth century western farmers converted their corn into whiskey to make a profit (Rorabaugh 1979). Archer Daniels Midland, a large grain processing company, came up with the same scheme in the 20th century. But ethanol was a product in search of a market, so ADM spent three decades relentlessly pushing for ethanol to be used in gasoline. Today ADM is making record profits from ethanol sales and government subsidies. (Barrionuevo 2006).

The Department of Energy hopes to have biomass supply 5% of the nation's power, 20% of transportation fuels, and 25% of chemicals by 2030. These combined goals are 30% of the current petroleum consumption.

Fuels made from biomass are a lot like the nuclear powered airplanes the Air Force tried to build from 1946 to 1961, for billions of dollars. They never got off the ground. The idea was interesting – atomic jets could fly for months without refueling. But the lead shielding to protect the crew and several months of food and water was too heavy for the plane to take off. The weight problem, the ease of shooting this behemoth down, and the consequences of a crash landing were so obvious, it's amazing the project was ever funded, let alone kept going for 15 years.

Biomass fuels have equally obvious and predictable reasons for failure. H. T. Odum says that time explains why renewable energy provides such low energy yields compared to non-renewable fossil fuels. The more work left to nature, the higher the energy yield, but the longer the time required. Although coal and oil took millions of years to form into dense, concentrated solar power, all we had to do was extract and transport them (Odum 1996)

With every step required to transform a fuel into energy, there is less and less energy yield. For example, to make ethanol from corn grain, which is how all ethanol is made now, corn is first grown to develop hybrid seeds, which are planted, harvested, delivered, stored, and preprocessed to remove rocks and dirt. Ethanol made in a dry-mill is milled, liquefied, heated, saccharified, fermented, evaporated, centrifuged, distilled, scrubbed, dried, stored, and transported to customers (McAloon 2000).

Fuels from biomass are not sustainable, have a net energy loss, and there isn't enough biomass in America to make significant amounts of energy. After more than thirty years of research, cellulosic ethanol still has major problems. Essential inputs like water, land, natural gas, and phosphate ores are limited. Deforestation to open up more farmland, irrigation, and too much biomass removal destroys fertile soil. You end up with a country like Iraq, formerly Mesopotamia, where 75% of the farm land is a salty desert.

Soil Science 101 – there is no "waste" biomass

Long before there was "Peak Oil", there was "Peak Soil". Iowa has some of the best topsoil in the world, yet in the past century it's eroded from an average of 18 inches to less than 10 inches (Pate 2004, Klee 1991). When topsoil reaches 6 inches or less (the average depth of the root zone in crops), productivity drops off sharply (Sundquist 2005).

Soil erodes geologically at a rate of about 400 pounds of soil per acre per year (Troeh 2005). But on over half of America's best crop land, the erosion rate is 11,000 pounds per acre, 27 times the natural rate, and double that on the worst 7% of cropland (NCRS 2006), partly because farmers aren't paid to conserve their land, and partly because hired farmers wrench every penny of profit they can on behalf of short-sighted owners.

Erosion is happening ten to twenty times faster than the rate topsoil can be formed by natural processes (Pimentel 2006).

That might make the average person concerned. But not the USDA -- they've redefined erosion as the average soil loss that could occur without causing a decline in long term productivity. Yet crop productivity continually declines as topsoil is lost and residues are removed. (Al-Kaisi May 2001, Ball 2005, Blanco-Canqui 2006, BOA 1986, Calviño 2003, Franzleubbers 2006, Grandy 2006, Johnson 2004, Johnson 2005, Miranowski 1984, Power 1998, Sadras 2001, Troeh 2005, Wilhelm 2004).

Troeh (2005) believes that the tolerable soil loss (T) value is set too high, because it's based only on the upper layers -- how long it takes subsoil to be converted into topsoil. T ought to be based on deeper layers – the time for subsoil to develop from parent material or parent material from rock. If he's right, erosion is even worse than official figures.

Erosion removes the most fertile parts of the soil (USDA-ARS). When you feed the soil with fertilizer or manure, you're not feeding plants; you're feeding the biota in the soil. Underground creatures and fungi break down fallen leaves and twigs into microscopic bits that plants can eat, and create tunnels air and water can infiltrate. In nature there are no elves feeding (fertilizing) the wild lands. When plants die, they're recycled into basic elements and become a part of new plants. It's a closed cycle. There is no bio-waste.

There's so much life underground there can be 10 "biomass horses" for every horse grazing above on an acre of pasture (Wardle 2004). If you dove into the soil and swam around, you'd be surrounded by miles of thin strands of mycorrhizal fungi that help plant roots absorb more nutrients and water, plus millions of creatures, most of them unknown. There'd be thousands of species in just a handful of earth –- springtails, bacteria, and worms digging airy subways. As you swam along, plant roots would tower above you like trees as you wove through towering underground apartments.

Soil creatures and fungi act as an immune system for plants against diseases, weeds, and insects – when this living community is harmed by agricultural chemicals and fertilizers, even more chemicals are needed in an increasing vicious cycle. (Wolfe 2001).

Plants and creatures underground need to drink, eat, and breathe just like we do. An ideal soil is half rock, and a quarter each water and air. When tractors plant, harvest, and cull weeds, they crush the life out of the soil as underground apartments collapse 9/11 style. The tracks left by tractors in the soil are the erosion route for half of the soil that washes or blows away (Wilhelm 2004).

Agriculture is not sustainable the way it's being practiced now. But ethanol from corn is agriculture on steroids because: Corn uses more water and chemicals, causing more erosion than most crops.

• Farmers are starting to plant corn in dry western states with limited water, and corn crop after corn crop instead of rotating corn with other crops.

• The government has studied the effect of growing corn crop after corn crop and found it increases eutrophication by 189%, global warming by 71%, and acidification by 6% (Powers 2005). Less crop rotation leads to more plant disease and an increased need for fertilizers and pesticides. • The Conservation Reserve Program (CRP) pays farmers not to grow corn on highly-erodible, water protecting, or wildlife sustaining land. But with such high corn prices, farmers are asking the Agricultural Department to release them early from these contracts so they can plant corn on these low-producing, environmentally sensitive lands (Tomson 2007).

• Making cellulosic ethanol from crop residues -- the parts of the plant we don't eat (stalk, roots, and leaves) – will make matters even worse since the residues are essential for soil nutrition, preventing erosion, retaining more water, and putting carbon back into the soil.

Growing plants for fuel will accelerate the already unacceptable and unsustainable levels of topsoil erosion, soil compaction, soil carbon and nutrient depletion, poor soil structure, less ability of soils to retain water, water depletion and pollution, air pollution, eutrophication and destruction of fisheries, siltation of dams and waterways, salination, loss of biodiversity, and damage to human health in the United States (Tegtmeier 2004). This all leads to in lower crop production and eventually turns the land into a desert.

Why are soil scientists absent from the biofuels debate?

Out of curiosity I wrote 35 mostly university soil scientists to ask why soil science wasn't part of the biofuels debate. These are just a few of the responses from the ten who replied to my off-the-record poll (so far no one has allowed me to quote them):

• …" I have no idea why soil scientists aren't questioning corn ethanol and cellulosic ethanol plans. Quite frankly I am not sure that our society has had any sort of reasonable debate about this with all the facts laid out. When you see that the plan is to convert all of the corn to ethanol and that this will not provide more than 20% of our current liquid fuel use, it certainly makes me wonder even before considering the conversion efficiency, soil loss, water contamination, food price problems, etc".

• "One of the problems for scientists is that as academics working for state governments, some of us are actually not allowed to talk about things with policy makers unless asked by them". • Biomass production is not sustainable. Only business men and women in the refinery business believe it is.

• "Should we be using our best crop land to grow gasoline and contribute further to global warming? What will our children grow their food on?"

• "As agricultural scientists, we are programmed to do what it takes to make and keep farmer's profitable, therefore profits, euphemistically known as "economic sustainability" is on the top of the list and not necessarily compatible with farm, soil, family or environmental sustainability".

• "Government policy since the end of WWII has been to encourage overproduction to keep food prices down (people with full bellies don't revolt or object too much). It's hard to make a living farming commodities when the selling price is always at or below the break even point. Farmers have had to get bigger and bigger to make ends meet since the margins keep getting thinner and thinner. We have sacrificed our family farms in the name of cheap food. When farmers stand to make few bucks (as with biofuels) agricultural scientists tend to look the other way".

• You are quite correct in your concern that soil science should be factored into decisions about biofuel production. Unfortunately, we soil scientists have missed the boat on the importance of soil management to the sustainability of biomass production, and the long-term impact for soil productivity.

Natural Gas in Agriculture

Soils that are farmed must be fed to be sustained. The nutrition of removed biomass has to be replaced. In the past this was done with residues, manure, and compost, which unlike fertilizer, improved soil structure and health, decreased erosion and water evaporation, and increased water retention.

Now the biomass is replaced with fertilizer. "Fertilizer energy" accounts for 28% of the energy used in agriculture (Heller, 2000). Fertilizer not only uses natural gas as a feedstock, it uses natural gas to create the high temperatures and pressures necessary to coax inert nitrogen out of the air (nitrogen is often the limiting factor in crop production). This is known as the Haber-Bosch process, and it's a big part of the green revolution that made it possible for the world's population to grow from half a billion to 6.5 billion today. (Smil 2000, Fisher 2001).

Natural gas has become so expensive that we are getting more dependent on imported fertilizers. In 2005 we imported 148% more Anhydrous Ammonia, 93% more Urea (solid), and 349 % more of other nitrogen fertilizers than in 1995 (USDA ERS).

The best possible way to increase national security and become less vulnerable to high-priced fertilizer imports plus improve the quantity and quality of our topsoil, would be to return crop residues to the land as fertilizer, not to make cellulosic ethanol.

Agriculture competes with homes and industry for fast depleting North American natural gas; natural gas can't be imported as Liquefied Natural Gas significan tly for many years. Natural gas price increases have already caused many businesses to fail and over 280,000 jobs have been lost (Gerard 2006). Natural gas is also used for heating and cooking in half our homes, generates about a fifth of United States electricity, and is a feedstock for thousands of products (chemicals, plastics, carpets).

Natural gas based fertilizers that replace biomass, and natural gas used to run ethanol refineries, is unavailable to businesses, homes, and natural gas vehicle fleets.

Energy Returned on Energy Invested (EROEI or EROI)

To understand the concept of EROEI, imagine a magician doing a variation on the rabbit-out-of-a-hat trick. He strides onstage with a rabbit, puts it into a top hat, and then spends the next five minutes pulling 100 more rabbits out. That is a pretty good return on investment!

Oil was like that in the beginning: one barrel of oil of energy was required to get 100 more out, or an Energy Returned on Energy Invested (EROEI) of 100:1.

When the biofuel magician tries to do the same trick decades later, he puts the rabbit into the hat, and pulls out only one pooping rabbit. The excrement is known as byproduct in the ethanol industry.

Studies that show a positive energy gain for ethanol would show a negative return if the byproduct were left out (Farrell, 2006). Here's where byproduct comes from: if you made ethanol from corn in your back yard, you'd dump a bushel of corn and two gallons of water, and yeast into your contraption. Out would come 18 pounds of ethanol, 18 pounds of CO2, and 18 pounds of byproduct – the leftover corn solids.

Patzek and Pimentel believe you shouldn't include the energy contained in the byproduct, because you need to return it to the soil to improve nutrition and soil structure (Patzek June 2006). Giampetro believes the byproduct should be treated as a "serious waste disposal problem and … an energy cost", because if we supplied 10% of our energy from biomass, we'd generate 37 times more livestock feed than is used (Giampetro 1997).

It's even worse than Giampetro realized – he didn't know most of this "livestock feed" can't be fed to livestock because it's too energy and monetarily expensive to deliver – especially short-lived heavy wet distillers byproduct, which succumbs to mold and fungi after 4 to 10 days. Also, byproduct is a subset of what animals eat. Cattle are fed byproduct in 20% of their diet at most. Iowa's a big hog state, but commercial swine operations feed pigs a maximum of 5 to 10% byproduct (Trenkle 2006; Shurson 2003).

Worst of all, the EROEI of ethanol is 1.2 :1 or 1.2 units of energy out for every unit of energy in, a gain of ".2". The "1" in "1.2" represents the liquid ethanol. What is the ".2" then? It's the rabbit feces – the byproduct. So you have no ethanol for your car, because the liquid "1" needs to be used to make more ethanol. That leaves you with just the ".2" --- a bucket of byproduct to feed your horse – you do have a horse, don't you? If horses are like cattle, then you can only use your byproduct for one-fifth of his diet, so you'll need four supplemental buckets of hay from your back yard to feed him. No doubt the byproduct could be used to make other things, but that would take energy.

Researchers who find a positive EROEI for ethanol have not accounted for all of the energy inputs. For example, Shapouri admits the "energy used in the production of secondary inputs, such as farm machinery and equipment used in corn production, and cement, steel, and stainless steel used in the construction of ethanol plants, are not included". (Shapouri 2002). Or they assign overstated values of ethanol yield from corn (Patzek Dec 2006). Many, many, other inputs are left out.

Patzek and Pimentel have compelling evidence showing that about 30 percent more fossil energy is required to produce a gallon of ethanol than you get from it. Their papers are published in peer-reviewed journals where their data and methods are public, unlike many of the positive net energy results.

Infrastructure. Current EROEI figures don't take into account the delivery infrastructure that needs to be built. E85 ethanol corrodes seals and gaskets, that's why special E85 cars need to be made. It will take 10-15 years to replace half of the 245 million cars and light trucks in the United States to burn E85, and E80 vehicles would require engine design modifications. It would take over $544 million dollars of delivery ethanol infrastructure (Reynolds 2002 case B1) and $5 to $34 billion to revamp 170,000 gas stations nationwide (Heinson 2007).

The EROEI of oil when we built most of the infrastructure in this country was about 100:1, and it's about 25:1 worldwide now. Even if you believe ethanol has a positive EROEI, you'd probably need at least an EROEI of at least 5 to maintain modern civilization, so 1.2:1 isn't good enough (Hall 2003).

Of the four articles that showed a positive net energy for ethanol in Farrells 2006 Science article, three were not peer-reviewed. The only positive peer-reviewed article (Dias De Oliveira, 2005) states "The use of ethanol as a substitute for gasoline proved to be neither a sustainable nor an environmentally friendly option" and the "environmental impacts outweigh its benefits". Dias De Oliveria concluded there'd be a tremendous loss of biodiversity, and if all vehicles ran on E85 and their numbers grew by 4% per year, by 2048, the entire country, except for cities, would be covered with corn.

The boundaries of what is included in net energy calculations are kept as narrow as possible to reach positive results. The energy to remediate environmental damage is left out entirely.

Eutrophication. Farm runoff of nitrogen fertilizers has contributed to the hypoxia (low oxygen) of rivers and lakes across the country and the dead zone in the Gulf of Mexico. Yet the cost of the lost fisheries are not subtracted from the EROEI of ethanol.

Soil erosion. Corn and soybeans have higher than average erosion rates. Eroded soil pollutes air, fills up reservoirs, and shortens the time dams can store water and / or generate electricity. Yet the energy of the hydropower lost to siltation, energy to remediate flood damage (eroded soil raises river-bed elevations and fills up drainage ditches), energy of increased dredging of dams, harbors, and navigation channels, aren't considered in EROEI calculations.

Climate change could lead to 33% to 274% increased soil loss, depending on the region (O'Neal 2005).

The worst areas of erosion are the areas with the most rented farmland. More than half the best farmland in the United States is rented: 65% in Iowa, 74% in Minnesota, 84% in Illinois, and 86% in Indiana. Owners seeking short-term profits have far less incentive than farmers who work their land to preserve soil and water. http://www.ers.usda.gov/Briefing/ConservationAndEnvironment/Gallery/sediment.htm

Water pollution. Soil erosion is a serious source of water pollution since it can wash pesticides that have had no chance to decompose directly into streams. Fish take up insecticides and when consumed these insecticides work their way up the food chain (Troeh 2005).

Ethanol plants pollute water. They generate 12 gallons of waste water for every gallon of ethanol produced.

Water depletion. Biofuel factories use a huge amount of water – four gallons for every gallon of ethanol produced. Despite 30 inches of rain per year in Iowa, there may not be enough water for both a mature corn ethanol industry and people and industry. Drought years will make matters worse (Cruse 2006).

Fifty percent of Americans rely on groundwater (Glennon 2002), and in many states, this groundwater is being depleted by agriculture faster than it is being recharged. This is already threatening current food supplies (Giampetro 1997). In some western irrigated corn acreage, groundwater is being mined at a rate 25% faster than the natural recharge of its aquifer (Pimentel 2003). Global warming. Farrell found ethanol made with natural gas only marginally better than gas from refineries in terms of carbon dioxide emissions and global warming, and worse if coal is burned in the process (Farrell 2006). Driving a mile on ethanol from a coal-using biorefinery releases more carbon dioxide than a mile on gasoline (Ward 2007). Coal in ethanol production is seen as a way to displace petroleum (Farrell 2006, Yacobucci 2006) and it's already happening (Clayton 2006). Harvesting biomass for biofuels increases global warming because the carbon in the plant is removed instead of incorporated into the soil

Biodiversity. Every acre of land removed from nature to grow crops destroys yet more biodiversity.

Rainforest destruction. Fires to clear land for palm oil plantations are destroying one of the last great remaining rainforests in Borneo, spewing so much carbon that Indonesia is third behind the United States and China in releasing greenhouse gases. Orangutans, rhinos, tigers and thousands of other species may be driven extinct (Monbiot 2005). Borneo palm oil plantation lands have grown 2,500% since 1984 (Barta 2006).

Soybeans cause even more erosion than corn and suffer from all the same sustainability issues. The Amazon is being destroyed by farmers growing soybeans for food (National Geographic Jan 2007).and fuel (Olmstead 2006).

Biodiesel

The idea we could run our economy on discarded fried food grease is very amusing. For starters, you'd need to feed 7 million heavy diesel trucks getting less than 8 mpg. Seems like we're all going to need to eat a lot more french fries, but if anyone can pull it off, it would be Americans. Spin it as a patriotic duty and you'd see people out the door before the TV ad finished, the most popular government edict ever.

Biodiesel is not ready for prime time. Although John Deere is working on fuel additives and technologies to burn more than 5% accredited biodiesel (made to ASTM D6751 specifications – vegetable oil does not qualify), that is a long way off in the future. 52 billion gallons of diesel fuel are consumed a year in the United States, but only 75 million gallons of biodiesel were produced– two-tenths of one percent of what's needed. To get the country to the point where gasoline was mixed with 5 percent biodiesel would require 64 percent of the soybean crop and 71,875 square miles of land (Borgman 2007), an area the size of the state of Washington. Soybeans cause even more erosion than corn.

Currently, biodiesel concentrations higher than 5 percent can cause "water in the fuel due to storage problems, foreign material plugging filters…, fuel system seal and gasket failure, fuel gelling in cold weather, crankcase dilution, injection pump failure due to water ingestion, power loss, and, in some instances, can be detrimental to long engine life" (Borgman 2007). Biodiesel also has a short shelf life and it's hard to store – it easily absorbs moisture (water is a bane to combustion engines),oxidizes, and gets contaminated with microbes. It increases engine NOx emissions (ozone) and has thermal degradation at high temperatures (John Deere 2006).

So much for running the most vital component of our economy even partially on "renewable" fuels.

Cellulosic Ethanol (see Appendix A for a summary of the problems)

Many plants want animals to eat their seed and fruit to disperse them. Some seeds only germinate after going through an animal gut and coming out in ready-made fertilizer. Seeds and fruits are easy to digest compared to the rest of the plant, that's why all of the commercial ethanol and biodiesel are made from the yummy parts of plants that we like to eat too, the grain portion rather than the stalks, leaves, and roots.

But plants don't want to be entirely devoured. They've spent hundreds of millions of years perfecting structures that can't easily be eaten. Be thankful plants figured this out, or everything would be mown down to bedrock.

If we ever did figure out how to break down cellulose in our back yard stills, it wouldn't be long before the 6.5 billion people on the planet destroyed the grasslands and forests of the world to power generators and motorbikes (Huber 2006)

Don Augenstein and John Benemann, who've been researching biofuels for over 30 years, are very skeptical as well. According to them, "…severe barriers remain to ethanol from lignocellulose. The barriers look as daunting as they did 30 years ago".

Benemann says the EROEI can be easily determined to be about five times as much energy required to make cellulosic ethanol than the energy contained in the ethanol.

The success of cellulosic ethanol depends on finding or engineering organisms that can tolerate extremely high concentrations of ethanol. Augenstein argues that this creature would already exist if it were possible. Organisms have had a billion years of optimization through evolution to develop a tolerance to high ethanol levels (Benemann 2006). Someone making beer, wine, or moonshine would have already discovered this creature if it existed.

The variety of biomass, even the range of chemical and physical properties in just corn stover (Ruth 2003, Sluiter 2000), means cellulosic ethanol plants can never be optimally efficient, because enzymes and chemical processes can't be tuned to such wide feedstock variance.

One of the motivations behind developing cellulosic ethanol is the high cost of delivery of corn grain ethanol from the Midwest to the coasts, since ethanol can't be delivered inexpensively through pipelines but must be transported by truck, rail, or barge (Yacobucci 2003).

Where will the Billion Tons of Biomass for Cellulosic Fuels Come From?

There isn't enough biomass to displace 30% of our petroleum use. The potential biomass from energy is miniscule compared to the mainly fossil fuel energy we consume every year, about 105 exa joules (EJ) in the USA. If you cut down every tree, corn field, and blade of grass and dug out all the roots in the United States, and burned them to get energy, you'd have 94 EJ of energy that year and we could all pretend we lived on Mars. Most of this 94 EJ of biomass is already spoken for – crops for food and feed, and wood for paper and homes. Sparse vegetation and the 30 EJ in root systems are economically unavailable – leaving only a small amount of biomass unspoken for (Patzek June 2006).

The government believes there is a billion tons of biomass "waste" to make cellulosic biofuels, chemicals, and generate electricity with. 400 million tons of this would come from crop residues, and 70%, or 280 million tons, from corn stover -- what's left after the corn is harvested. (DOE Feedstock Roadmap, DOE Biomass Plan).

There aren't 400 million tons of crop residue – this estimate assumes fantasy yields 50% higher than current yields, all land in no-till even though only about 20% is, and 75% of the residue would be harvested (Patzek, Nov 2006). Many tons will be lost in bad weather and storage. Other tons will go to non-biofuel customers.

Plants can only fix a tiny part of solar energy into plant matter every year -- about .1 to .5 percent new growth in temperate climates, restricting sustainable harvesting to at most one part in two hundred for use as fuel.

Nelson estimates that to prevent erosion, you could only harvest 51 million tons of corn and wheat residues (Nelson, 2002). Other factors, like soil structure, soil compression, water depletion, and environmental damage weren't considered. Fifty one million tons of residue could make about 3.8 billion gallons of ethanol, less than 1% of the energy needs.

Using corn stover is a problem, because corn, soy, and other row crops cause 50 times more soil erosion than sod crops (Sullivan 2004) or more (Al-Kaisi 2000), and corn also uses more water, insecticides and fertilizers than most crops. (Pimentel 2003). It would be better to get biomass from cereal grain straw, because grains use far less water and cause less erosion than row crops like corn and soybeans. But that isn't going to happen, because the green revolution fed billions more people by shortening grain height so that plant energy went into the edible seed, leaving little straw for biofuels.

Biomass Energy Crops

There aren't enough acres of land to grow significant amounts of low-yield biofuel energy crops like switchgrass. Land with switchgrass is usually of poor quality and highly erodible, farmers are paid not to farm much of this land, which would only produce about 2 tons of switchgrass biofuels per acre. Many acres in switchgrass now are already being used for wildlife and recreation.

Much of the area proposed for energy crops doesn't have enough water or adequate drainage to build an ethanol factory. Biorefineries can't be built just anywhere – they have to be on main roads, near railroad and natural gas lines, out of floodplains on parcels of at least 40 acres to provide storage for the residues, have electric power, and enough biofuel nearby to supply the plant year round – very few sites could be found to build switchgrass plants in all of South Dakota (Wu 1998).

Farmers won't grow switchgrass until there's a switchgrass plant and machines to harvest and transport switchgrass efficiently don't exist yet (Barrionuevo 2006), and the capital to build the switchgrass plant won't materialize until there are switchgrass farmers. Since Pimentel and Patzek found "ethanol production using switchgrass required 50% more fossil energy than the ethanol fuel produced", investors for these plants will be hard to find (Pimentel 2005).

Because switchgrass grows so well on marginal land, it's assumed that it's a miraculous plant that's escaped the water and nutrition needs of food crops. But studies have shown the more rainfall, the more switchgrass you get, and if you remove switchgrass, you're going to need to fertilize the land to replace the lost biomass, or you'll get continually lower yields of switchgrass every time you harvest the crop (Vogel 2002).

Like all other monoculture crops, ultimately yields of switchgrass will be reduced due to "pest problems, diseases, and soil degradation" (Giampetro, 1997).

These fast-growing disease-resistant plants are potentially bioinvasive, another kudzu. Bioinvasion costs our country billions of dollars a year. (Bright, 1998). Johnson grass was introduced as a forage grass and it's now an invasive weed in many states. Another fast-growing grass, Miscanthus, is now being proposed as a biofuel. It's been described as "Johnson grass on steroids" (Raghu 2006).

Sugar cane. Brazil uses oil for 90 percent of their energy. Brazilian ethanol production in 2003 was 3.3 billion gallons, about the same as the USA in 2004, or 1% of our transportation energy. Brazil uses 85% of their cane ethanol, leaving only 15% for export.

Although we grow some sugar cane in Florida thanks to the sugar lobby, despite tremendous amounts of environmental damage (WWF) and jacking up the price of sugar higher than what imports cost, we're too far north to grow a significant amount of sugar cane or other fast growing C4 plants.

Sugar cane has been touted as an "all you need is sunshine" plant. But according to the FAO, the nitrogen, phosphate, and potassium requirements of sugar cane are roughly similar to maize (FAO 2004)

Farmers aren't Stupid

Farmers are some of the smartest people on earth or they soon go out of business. They have to know everything from soil science and repairing equipment to commodity futures.

Crop production is reduced when residues are removed from the soil. Why would farmers want to sell their residues? Why would they want to spend money on yet-to-be-invented expensive corn and stover harvesting equipment?

Harvesting of stover on the scale needed to fuel a cellulosic industry won't happen because farmers aren't stupid, especially the ones who own and work their land. Although there is a wide range of opinion about the amount of residue that can be harvested safely without causing erosion and harming soil tilth, many farmers will want to be on the safe side, and stick with the studies showing that 20% (Nelson, 2002) to 30% (McAloon et al., 2000; Sheehan, 2003) at most can be harvested, not the 75% agribusiness claims is possible. Farmers also care about water quality (Lal, 1998; Mann et al, 2002). And farmers will decide that permanent soil compression is not worth any amount of money (Wilhelm 2004). As prices of fertilizer inexorably rise due to natural gas depletion, it will be cheaper to return residues to the soil than to buy fertilizer.

The further the farmer is from the biorefinery or railroad, the slimmer the profit, and the less likely a farmer will want the extra headache and cost of hiring and scheduling many different harvesting, collection, baling, and transportation contractors for corn stover.

Farm managers working for distant owners are more likely to sell crops and residues since they're concerned with generating profits for the owner, not preservation of the land long-term. But even they will sell to the highest bidder, which might be the livestock and dairy industry, furfural factories, hydromulching companies, biocomposite manufacturers, pulp mills, or city dwellers faced with skyrocketing utility bills, since the high heating value has twice the energy of the converted ethanol.

If the farmers can't supply enough crop residues to fuel the large biorefinery in their region, who will put up the capital to build one? Investors aren't stupid either.

Can biomass be collected, stored, transported, and preprocessed economically?

Harvesting. Residues are shredded to dry them out, then mowed, raked, baled, and loaded on a truck. This typically takes three additional tractor runs after the grain is harvested (Wilhelm 2004), which would triple the compaction damage to the soil (Troeh 2005), increase CO2, add to labor costs, and put unwanted foreign matter into the bale (soil, rocks, baling wire, etc).

There will be many rainy seasons when residues can't be harvested, because the field would get compacted, or the residue is too wet or decomposed. Waiting for the residue to dry out requires time not normally available during harvest. If the farmer waits anyhow and snow falls, the quantity and quality will be reduced.

So biomass roadmaps call for a new type of tractor or attachment to harvest both corn and stover in one pass. But then the tractor would need to be much larger and heavier – so much weight it could cause decades-long or even permanent soil compaction and increased erosion in the wide tire tracks. Farmers worry that mixing corn and stover might harm the quality of the grain. Increased mechanization is not the best long-term direction in a world of depleting energy.

Baling. The current technology to harvest biomass is to put it into bales of hay. Hay is a dangerous commodity -- it can spontaneously combust, and once on fire, can't be extinguished, leading to fire loss and increased fire insurance costs. Somehow the bales have to be kept from combusting during the several months it takes to dry the bales from 50 to 15 percent moisture. A large, well drained, covered area is needed to vent fumes and dissipate heat. If the bales get wet they will compost. (Atchison 2004).

Baling was developed for hay and has been adapted to corn stover with limited success. Biorefineries need at least half a million tons of biomass on hand to smooth supply bumps, much greater than any bale system has been designed for. Pelletization is not an option, it's too expensive. Other options need to be found. (DOE Feedstock Roadmap)

To get around the problems of exploding hay bales, wet stover could be harvested. The moisture content needs to be around 60 percent, which means a lot of water will be transported, adding to the delivery cost.

Storage. Stover needs to be stored with a moisture content of 15% or less, but it's typically 35-50%, and rain or snow during harvest will raise these levels even higher (DOE Feedstock Roadmap). If it's harvested wet anyhow, there'll be high or complete losses of biomass in storage (Atchison 2004).

Residues could be stored wet, as they are in ensilage, but a great deal of R&D are needed and to see if there are disease, pest, emission, runoff, groundwater contamination, dust, mold, or odor control problems. The amount of required water is unknown. The transit time must be short, or aerobic microbial activity will damage it. The wet biomass must be taken immediately to be washed, shredded, and transported to a drainage pad under a roof for storage, instead of baled when drier and left at the farm. The wet residues are heavy, making transportation costlier than for dry residues, perhaps uneconomical. It can freeze in the winter making it hard to handle. If the moisture is too low, air gets in, making aerobic fermentation possible, resulting in molds and spoilage.

Transportation. Although a 6,000 dry ton per day biorefinery would have 33% lower costs, the price of gas and diesel limits the distance the biofuel refinery can be from farms, reducing the "economies of scale" achieved by large refineries, so a 2,000 dry ton per day biorefinery is the largest size that might be feasible. Even this smaller refinery would require 200 trucks per hour (7 x 24) delivering biomass during harvest season, or 100 trucks per day if satellite sites are used for storage. This plant would need 90% of the crop residues from the surrounding 7,000 square miles with half the farmers participating. When this biomass is delivered to the biorefinery, it will take up at least 100 acres of land stacked 25 feet high.

The average stover haul to the biorefinery would be 43 miles one way if these rosy assumptions all came true. (Perlack 2002). If less than 30% of the stover is available from bad weather or farmers unwilling to sell more for reasons covered above, the average one-way trip becomes 100 miles and the biorefinery is economically and energetically impossible.

There is also a shortage of truck drivers, the rail system can't handle any new capacity, trains are designed to operate between hubs, not intermodally (i.e. truck to train to truck), and it's not economical to transport biomass, ethanol, or byproduct to barges. The existing transportation system has not changed much for 30 years yet this congested, inadequate infrastructure somehow has to be used to transport large amounts of ethanol, biomass, and byproducts (Haney 2006).

Preprocessing. Residues need to be cleaned of dirt, stones, metal, before yet-to-be-invented instruments measure yet-to-be-determined physical and biomechanical properties, and undergo grinding, densification, or blending.

Cellulosic Biorefineries

There are over 60 barriers to be overcome in making cellulosic ethanol in Section III of the DOE "Roadmap for Agriculture Biomass Feedstock Supply in the United States" (DOE Feedstock Roadmap 2003). For example:

"Enzyme Biochemistry. Enzymes that exhibit high thermostability and substantial resistance to sugar end-product inhibition will be essential to fully realize enzyme-based sugar platform technology. The ability to develop such enzymes and consequently very low cost enzymatic hydrolysis technology requires increasing our understanding of the fundamental mechanisms underlying the biochemistry of enzymatic cellulose hydrolysis, including the impact of biomass structure on enzymatic cellulose decrystallization. Additional efforts aimed at understanding the role of cellulases and their interaction not only with cellulose but also the process environment is needed to affect further reductions in cellulase cost through improved production".

No wonder many of the issues with cellulosic ethanol aren't being discussed – there's no way to express the difficulties in a sound bite. But I'll try. Before cellulosic plants can be built:

• We need to be sure there's enough land and water to provide sustainable biomass • Residues can be harvested without soil erosion or compaction

• There's enough biomass despite bad weather, a short harvesting season, and competing industries

• Residues can be stored in widely varying climates without rotting or combusting • Biomass can be transported economically to a large bio-refinery.

• Better and cheaper ways must be found to remove impurities in all steps, cheap pretreatment reactors that resist acid and alkali attack built, biomass recalcitrance to hydrolysis (breaking down) overcome; inexpensive cellulose enzymes, catalysts, and fermentation organisms invented; biomass variation detected with yet-to-be invented process sensors and controls and coped with in all steps, all of this integrated, and markets for byproducts found.

• Delivery of ethanol and byproducts despite limited rail, trucks, and barges, All of the above needs to be done with a positive EROEI before a plant can be built. Scientists have been trying to solve these issues for over thirty years now.

Nevertheless, this area is worthy of research money, but not public funds for demonstration or commercial refineries. This is the best hope for replacing the half million products made by and with fossil fuels now.

Subsidies and Politics

How come there are over 116 ethanol plants with 79 under construction and 200 more planned? Subsidies and tax breaks.

Federal and state ethanol subsidies add up to 79 cents per liter (McCain 2003), with most of that going to the four large companies that control 71% of ethanol supplies. There is also a tax break of 5.3 cents per gallon for ethanol (Wall Street Journal 2002). An additional 51 cents per gallon goes mainly to the oil industry to get them to blend ethanol with gasoline.

In addition to the $8.4 billion per year subsidies for corn and ethanol production, the consumer pays an additional amount for beef, milk, and eggs, because corn diverted to ethanol raises the price of corn for the livestock industry.

Worst of all, the subsidies may never end, because Iowa plays a leading role in who's selected to be the next president. John McCain has softened his stand on ethanol (Birger 2006). All four senators in California and New York have pointed out that "ethanol subsidies are nothing but a way to funnel money to agribusiness and corn states at the expense of the rest of the country". (Washington Post, 2002).

"Once we have a corn-based technology up and running the political system will protect it," said Lawrence J. Goldstein, a board member at the Energy Policy Research Foundation. "We cannot afford to have 15 billion gallons of corn-based ethanol in 2015, and that's exactly where we are headed" (Barrionuevo 2007).

Let's stop the subsidies and see if ethanol can fly.

Conclusion

Soil is the bedrock of civilization (Perlin 1991, Ponting 1993). Biofuels are not renewable. Why would we destroy our topsoil, increase global warming, deplete and pollute groundwater, destroy fisheries, and use more energy than what's gained to make ethanol? Why would we do this to our children and grandchildren?

Perhaps it's a combination of pork barrel politics, an uninformed public, greedy agribusiness corporations, jobs for the Midwest, campaign money for politicians (Lavelle 2007), and desperation to provide liquid transportation fuels (Bucknell 1981, Hirsch 2005).

But this madness puts our national security at risk. Destruction of topsoil and collateral damage to water, fisheries, and food production will result in less food to eat or sell for petroleum and natural gas imports. Diversion of precious dwindling energy and money to impossible solutions is a threat to our nations' future.

Some good could come out of the ethanol fiasco if attention were paid to fixing the unsustainable and destructive aspects of industrial agriculture. Since part of what's driving the ethanol insanity is job creation, divert the subsidies and pork barrel money to erosion control and sustainable agriculture. Maybe Iowa will emerge from its makeover looking like Provence, and volunteers won't be needed to hand out free coffee at rest areas along I-80.

Continue to fund cellulosic research, focusing on how to make 500,000 fossil-fuel-based products (i.e. medicine, chemicals, plastics, etc). But don't use taxpayer money to build demonstration or commercial plants until most of the research problems have been resolved, especially finding enough sustainable biomass.

California and other states trying to implement global warming measures should not adopt the E10 ethanol blend. Biofuels are at best neutral and at worst contribute to global warming. A better early action item would be to favor low-emission vehicle sales and require all new cars to have energy efficient tires.

Take away the E85 loophole that allows the Big Three automakers to ignore café standards and get away with selling even more gas guzzling vehicles (Consumer Reports 2006).

Responsible politicians need to tell Americans why their love affair with the car can't continue. Leaders need to make the public understand that there are limits to growth, and an increasing population leads to the "Tragedy of the Commons". Even if it means they won't be re-elected. Arguing this amidst the church of development that prevails this is like walking into a Baptist church in Georgia and telling the congregation there is no God, but it must be done.

There are far better, faster, easier ways to stretch out petroleum than adding ethanol to it. Just keeping tires inflated properly would save more energy than all the ethanol produced today. Reducing the speed limit to 55, consumer driving tips, truck stop electrification, and many other measures can save far more fuel in a shorter time than biofuels ever will, far less destructively. Better yet, Americans can bike or walk, which will save energy used in the health care system.

Here are just a few possibilities for reforming the current, non-sustainable, agricultural system:

• The National Resources Conservation Service (NCRS) and other conservation agencies have done a superb job of lowering the erosion rate since the dustbowl of the 1930's. Give these agencies a larger budget to further the effort.

• The worst aquifer depletion and erosion are taking place on rented farmland. Tax and zoning laws need to be changed to support small and medium family farms. This will make possible the "social, economic, and environmental diversity necessary for agricultural and ecosystem stability" (Opie 2000).

• Make the land grant universities follow the directive of the Hatch Act of 1887 to improve the lives of family farms, rather than mechanize agriculture and chemical warfare for the benefit of the largest farms (Hightower 1978).

• Immediately begin well-funded sustainable agriculture programs at universities and community colleges across America to train a new generation of farmers.

• Integrate livestock into the crop rotation.

• Teach urban and suburban homeowners how to grow the most food in limited space with biointensive techniques.

• Fund the many institutions and agencies that have sustainable agriculture and "green ticket" plans to improve current methods of agriculture.

We are still betting the farm on making cellulosic ethanol work at a time when our energy and financial resources are diminishing. Living in the moment might be enlightenment for individuals, but for a nation, only looking to the next quarter is disastrous. Is there a Plan B if biofuels don't work out? Liquefied coal is not an option given the effects of global warming, and we don't know how to sequester the carbon dioxide, which could trigger a Permian extinction level event (Ward 2006, Benton 2003).

There need to be plans for de-mechanization of the farm economy if liquid alternative energy sources aren't found. There are less than four million horses, donkeys, and mules in America today. According to Bucknell, if the farm economy were de-mechanized, you'd need at least 31 million farm workers and 61 million horses. (Bucknell 1981)

The population of the United States has grown over 25 percent since Bucknell published Energy and the National Defense. To de-mechanize now, we'd need 39 million farm workers and 76 million horses. The horsepower represented by just farm tractors only is the equivalent of 400 million horses.

We need to transition from petroleum power to muscle power gracefully if we want to preserve democracy. What is the carrying capacity of the nation? Is it 100 million (Pimentel 1991) or 250 million (Smil 2000)?

Do you want to eat or drive? Even without growing food for biofuels, crop production per capita is going to go down as population increases, fossil fuel energy decreases, topsoil loss continues, and aquifers deplete, especially the Ogallala (Opie 2000). Where will the money come from to buy imported oil and natural gas if we don't have food to export?

There is no such thing as "waste" biomass. As we go down the energy ladder, plants will increasingly be needed to stabilize climate, provide food, medicine, shelter, furniture, heat, light, cooking fuel, clothing, etc.

Biofuels are a threat to the long-term national security of our nation. Is Dr. Strangelove in charge, with a plan to solve defense worries by creating a country that's such a salty polluted desert, no one would want to invade us? Why is Dr. Strangelove spending the last bits of energy in Uncle Sam's pocket on moonshine? Perhaps he's thinking that we're all going to need a lot, and the way things are going, he may be right.

Appendix A: Department of Energy Roadmap Barriers

I'm not the only one who finds ethanol problematic. This is a partial summary of biofuel problems from Department of Energy roadmaps that detail barriers to using biomass as a fuel. Unless otherwise footnoted, the problems with biomass fuel production are from the Multi Year Program Plan DOE Biomass Plan or Roadmap for Agriculture Biomass Feedstock Supply in the United States. (DOE Biomass Plan, DOE Feedstock Roadmap).

Resource and Sustainability Barriers 1) Biomass feedstock will ultimately be limited by finite amounts of land and water 2) Biomass production may not be sustainable because of impacts on soil compaction, erosion, carbon, and nutrition. 3) Nor is it clear that perennial energy crops are sustainable, since not enough is known about their water and fertilizer needs, harvesting impacts on the soil, etc. 4) Farmers are concerned about the long-term effects on soil, crop productivity, and the return on investment when collecting residues. 5) The effects of biomass feedstock production on water flows and water quality are unknown 6) The risks of impact on biodiversity and public lands haven't been assessed.

Economic Barriers (or Investors Aren't Stupid) 1) Biomass can't compete economically with fossil fuels in transportation, chemicals, or electrical generation. 2) There aren't any credible data on price, location, quality and quantity of biomass. 3) Genetically-modified energy crops worry investors because they may create risks to native populations of related species and affect the value of the grain. 4) Biomass is inherently more expensive than fossil fuel refineries because a) Biomass is of such low density that it can't be transported over large distances economically. Yet analysis has shown that biomass plants need to be large to be economically attractive – it will be difficult to find near enough biomass close to be delivered economically. b) Biomass feedstock amounts are unpredictable since unknown quantities will be lost to extreme weather, sold to non-biofuel businesses, rot or combust in storage, or by used by farmers to improve their soil. c) Ethanol can't be delivered in pipelines due to likely water contamination. Delivery by truck, barge, and rail is more expensive. Ethanol is a hazardous commodity which adds to its transportation cost and handling. d) Biomass varies so widely in physical and chemical composition, size, shape, moisture levels, and density that it's difficult and expensive to supply, store, and process. e) The capital and operating costs are high to bale, stack, palletize, and transport residues f) Biomass is more geographically dispersed, and in much more ecologically sensitive areas than fossil resources. g) The synthesis gas produced has potentially higher levels of tars and particulates than fossil fuels. h) Biomass plants can't benefit from the same large-scale cost savings because biomass is too dispersed and of low density. 5) Consumers won't buy ethanol because it costs more than gasoline and contains 34% less energy per gallon. Consumer reports wrote they got the lowest fuel mileage in recent years from ethanol due to its low energy content compared to gasoline, effectively making ethanol $3.99 per gallon. Worse yet, automakers are getting fuel-economy credits for every E85 burning vehicle they sell, which lowers the overall mileage of auto fleets, which increases the amount of oil used and lessens energy independence. (Consumer Reports)

Equipment and Storage Barriers 1) There are no harvesting machines to harvest the wide range of residue from different crops, or to selectively harvest components of corn stover. 2) Current biomass harvesting and collection methods can't handle the many millions of tons of biomass that need to be collected. 3) How to store huge amounts of dry biomass hasn't been figured out. 4) No one knows how to store and handle vast quantities of different kinds of wet biomass. You can lose it all since it's prone to spoiling, rotting, and spontaneous combustion

Preprocessing Barriers 1) We don't even know what the optimum properties of biomass to produce biofuels are, let alone have instruments to measure these unknown qualities. 2) Incoming biomass has impurities that have to be gotten out before grinding, compacting, and blending, or you may damage equipment and foul chemical and biological processes downstream. 3) Harvest season for crops can be so short that it will be difficult to find the time to harvest cellulosic biomass and pre-process and store a year of feedstock stably. 4) Cellulosic biomass needs to be pretreated so that it's easier for enzymes to break down. Biomass has evolved for hundreds of millions of years to avoid chemical and biological degradation. How to overcome this reluctance isn't well enough understood yet to design efficient and cost-effective pre-treatments. 5) Pretreatment reactors are made of expensive materials to resist acid and alkalis at high temperatures for long periods. Cheaper reactors or low acid/alkali biomass is needed. 6) To create value added products, ways to biologically, chemically, and mechanically split components off (fractionate) need to be figured out. 7) Corn mash needs to be thoroughly sterilized before microorganisms are added, or a bad batch may ensue. Bad batches pollute waterways if improperly disposed of. (Patzek Dec 2006).

Cellulosic Ethanol Showstoppers 1) The enzymes used in cellulosic biomass production are too expensive. 2) An enzyme that breaks down cellulose must be found that isn't disabled by high heat or ethanol and other end-products, and other low cost enzymes for specific tasks in other processes are needed. 3) If these enzymes are found, then cheap methods to remove the impurities generated are needed. Impurities like acids, phenols, alkalis, and salts inhibit fermentation and can poison chemical catalysts. 4) Catalysts for hydrogenation, hydrgenolysis, dehydration, upgrading pyrolysis oils, and oxidation steps are essential to succeeding in producing chemicals, materials, and transportation fuels. These catalysts must be cheap, long-lasting, work well in fouled environments, and be 90% selective. 5) Ethanol production needs major improvements in finding robust organisms that utilize all sugars efficiently in impure environments. 6) Cheap, efficient fermentation organisms that can produce chemicals and materials is key to making the process economic. Wald writes that the bacteria scientists are trying to tame come from the guts of termites, and they're much harder to domesticate than yeast was. Nor have we yet convinced "them to multiply inside the unfamiliar confines of a 2,000-gallon stainless-steel tank" or "controlling their activity in the industrial-scale quantities needed" (Wald 2007). 7) Efficient aerobic fermentation organisms to lower capital fermentation costs. 8) Fermentation organisms that can make 95% pure fermentation products. 9) Cheap ways of removing impurities generated in fermentation and other steps are essential since the costs now are far too high.

Appendix B: Energy from Combustion of Biomass

Because biomass has absorbed heavy metals and other pollutants from sources like coal power plants, industry, and treated wood, combustion releases chlorinated dioxins, benzofurans, polycyclic aromatic hydrocarbons, cadmium, mercury, arsenic, lead, nickel, and zinc, which are energetically and monetarily expensive to control. Combustion contributes to global warming by adding nitrogen oxides and the carbon stored in plants back into the atmosphere, as well as removes agriculturally essential nitrogen and phosphate. (Reijnders 2006)

Problems that biomass combustion plants have to contend with are many, from producing, transporting, preparing, drying, burning, to toxic emissions. They are competing with companies that want this material for construction, mulch, compost, paper, and other profitable ventures, often driving the price of wood higher than a wood-burning biomass plant can afford. Much of the forest wood that could be burned is inaccessible due to a lack of roads.

Collecting it is very energy intensive, requiring some combination of bunchers, skidders, whole-tree choppers, or tub grinders, and then hauling it to the biomass plant.

Efficiency is lowered if material with a high water content is burned, like fresh wood, and the different physical and chemical characteristics of the fuel can lead to control problems (Badger 2002). When you burn wet substances, so much energy goes into vaporizing the water that very little energy emerges as heat, and drying takes time and energy.

Even more energy is used to chop feedstock into similar sizes and placed on a conveyor belt to be fed to the plant. Any alkali or chlorine released in combustion gets deposited on the equipment, reducing overall plant efficiencies, as well as accelerating corrosion and erosion of plant components, requiring high replacement and maintenance energy.

If biomass is co-fired with coal, it needs to be reduced to ¼ inch or less, and the resulting fly ash may not be marketable to the concrete industry. (Bain 2003)

Processing all materials with different physical properties is energy intensive, requiring sorting, handling, drying, and chopping. It's hard to optimize the pyrolysis, gasification, and combustion processes if different combustible fuels are used. Urban waste requires a lot of sorting, since it often has material that must be removed, like rocks and dirt, construction wallboard, concrete, metal, etc. The type of incoming material ranges from yard trimmings with high moisture content to chemically treated wood, cardboard, pallets, and so on.

California biomass plants weren't able to use crop residues because they had such low bulk density that they weren't viable In 2000, the viability of California biomass enterprise was in serious doubt because the energy to produce biomass was so high due to the small facilities and high cost of collecting and transporting material to the plants. . (Bain 2003)

Ethanol production using wood biomass required 57% more fossil energy than the ethanol fuel produced (Pimentel 2005).

Wood is a nonrenewable resource. Old-growth forests had very dense wood with a high energy content, but wood from fast-growing plantations is so low-density and low calorie it's not even good to burn in a fireplace. These plantations require energy to plant, fertilize, weed, thin, cut, and deliver. The trees are finally available for use after 20 to 90 years – too long for them to be considered a renewable fuel (Odum 1996).

There's not enough wood to fuel a civilization of 300 million people. Over half of North America was deforested by 1900, at a time when there were only 75 million people (Williams 2003). Most of this was from home use. In the 18th century the average Northeastern family used 20 to 60 cords of wood per year, and 10 to 20 cords when wood stoves became available. At least one acre of woods is required to sustainably harvest one cord of wood. (Whitney 1994)

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