Renewable Forests

By Scott Miller — March 2011

Forest Energy

Perspective is something one gains from understanding a diverse range of views. Unfortunately, forests and their potential for energy is something most people, particularly Americans, have a very narrow perspective of. Fully 75% of the U.S. population lives in major urban areas which are generally void of all forests. Yes, there are trees, but the role of forests in the survival and advancement of humans, as well as their potential for future advancements goes largely unmentioned in this nation.

In general, a forest is an area with a high density of trees. These collections of trees serve a variety of purposes for the environment. While most people understand the role of trees in cleaning the air, what is less recognized is the role of trees in cleaning water, improving soil, and capturing solar energy. Over their lifetimes, trees collect solar energy on a daily basis and convert this energy into their mass through photosynthesis. This process occurs with all plants but with forests, this energy conversion is occurring on a massive scale.

In total, the United States has slightly over 650 million acres of forests. Using existing technology and tree breeds, this land is capable of producing roughly 4.5 billion tons of biomass annually on a sustainable basis. This mass can be directly converted with existing technology into a total of about 11 billion barrels of synthetic fuels. Additionally, there are over 580 million other acres of land in the US currently used for grazing and open range areas that would be suitable for growing energy forests for biomass conversion. Obviously, it wouldn’t be prudent or wise to convert the entire forest and rangeland inventories of the US over to energy production. The point is that the forest and open range areas of the United States represent an area more than three and a half times the size of the agricultural cropland areas of the United States.
Land use in the United States size: 110 Kb - 4 pages

Logically, if we’re going to start “growing” energy, this is the place to begin due to the quantity of land available and the fact that this land has limited other uses today. Certainly there needs to be care taken to avoid major disruptions to large areas but we also need to keep in mind that nature itself often purges forests and rangelands by wildfires. Using current technology, forests are capable of providing energy by three distinct methods: forest residual biomass processing, biomass harvesting of the complete trees on a rotational basis and harvesting of the seeds/fruits of the trees only.

Forest Residual Biomass

Forest residuals are the materials left behind when forests are processed for other products. When trees are processed for wood and paper, significant portions of the tree such as the crown, small branches, bark and stump are not useable for the desired products. Currently these wastes are often burned on site or left to decay into nutrients for the soil. More waste materials (sawdust, dirty chips and black liquor) are generated at the mills where the trees are sawed into logs or converted to pulp. In some cases, entire trees may be wasted due to growth defects or disease depending on the breed.

A USDA study* suggesting potential biomass production in the U.S. came up with some surprisingly large estimates about how much waste is available from the existing forest products industries. Starting within the forests themselves, the study found 60 million tons of material available annually from operations to reduce fire hazards. Another 64 million tons is estimated for the residues from normal harvesting operations of existing forests. Still another 145 million tons is estimated for processing wastes at the various mills that convert the trees into products. In the final waste stage, an estimated 47 million tons of wood wastes are generated in urban areas from construction debris and various other wood sources. That’s a total estimate of 316 million dry tons of waste per year that basically gets landfilled or left to decay.
* Billion Ton Annual Supply size: 2.8 Mb - 75 pages

Using a technology called gasification, all of this waste material can be converted into various forms of energy. Many modern paper mills already incorporate older technologies for burning this biomass to reduce the electrical and steam requirements of the mills. Based on the USDA estimates, this is enough biomass to produce over 2.1 million barrels per day of synthetic fuels using nothing more than wastes. For some perspective, consider that only sixteen nations in the world produce a higher daily average of crude oil than 2.1 million barrels. If all of this was converted directly to synthetic oil, this one step would increase US oil production by 25% - I wouldn’t recommend converting it to oil, but that shows just how big of an impact this could make.

Biomass Harvesting

Trees grow at different rates depending on the breed of the tree. Some breeds grow at a steady rate throughout their life spans while others grow very rapidly early on. It is these early fast growing varieties that are the focus of biomass harvesting. In this process, trees are grown in large area plantations, much like agricultural crops but with dramatic reductions in the need for fertilizers and irrigation. As the trees grow, some are thinned out and processed while the rest of left to allow for more rapid growth. This thinning continues until the final stage when the remaining stands are cleared.
— Biomass Fuel from Woody Crops for Electric Power Generation

Biomass trees can also be processed using a method called coppicing. In this process, young trees are cut down cleanly near ground level. In following years, the stumps will produce new growth that is typically narrower, straighter and grows more vertically than natural tree growth. This method also allows for easier harvesting that can be automated. This method only works with certain species of tree, however most trees being considered for biomass fall within this category.

A key advantage of this approach compared to other energy crops is that fast growing varieties of trees are available for most climate and soil conditions. Trees like the poplar, willow, cottonwood, pawlonia and eucalyptus are all currently being studied for biomass potential. These breeds collectively can be grown in plantations in all Lower 48 states as well as Alaska. There are native species in all of these areas and most are capable of producing an average of 5-7 tons of biomass per year. Under optimum conditions, the right hybrids from these species can produce over 10 tons per year of biomass.

Seed/Fruit Harvesting

The above calculations assume harvesting and processing the trees through a process such as gasification. The beauty of the forests is that this isn’t the only option. Many types of trees produce non-edible oils in their seeds and pods. While the output isn’t huge on a per tree basis, when considered from the perspective of millions of acres of forests, the output can be substantial. In India, China and Brazil, active programs are harvesting fuel from breeds like the Honge and Jatropha trees. The Honge tree in particular is claimed to be capable of producing enough seeds when mature to produce nearly 50 barrels of honge oil per acre of trees. Honge oil can be converted relatively easily to a product comparable to biodiesel.

Where this technique could really get interesting is in ongoing research in genetically modified Chinese Tallow trees. The Tallow is an invasive species that has been cultivated in China for hundreds of years to harvest waxes and oil for candles and soaps. Originally introduced into the United States during the Colonial period, the Chinese Tallow is pervasive throughout the Carolinas, the Deep South and California. In some areas such as Houston Texas, the Tallow is the dominant tree found, outnumbering all other species.

The cultivation work of the Chinese with the Tallow was intended to optimize production of the waxy seeds – seeds which together with the waxes can be directly and efficiently converted into biodiesel fuel. Unlike other biomass plants that are currently in the research phase, the Chinese Tallow has been in commercial production outside the US for many years and has a documented record of average production of over 6 tons per acre per year of seed biomass – enough to produce about 645 gallons of biodiesel. From this same process, an additional 1400 lbs of protein rich meal (animal feed) and 5000lbs of additional biomass are generated. Gasification of the waste biomass makes another 260+ gallons of synthetic fuels available from the same acre giving us a total of over 900 gallons of renewable fuels per acre per year.

The only obvious downside today comes from the invasive nature of the species. In order to use this species for fuel production, it would be necessary to develop infertile breeds that could be cultivated plantation style in order to prevent the Tallow from overtaking existing plant breeds in the area. For some perspective, consider that an estimated 100,000 acres of land in Louisiana alone are estimated to be dominated by Tallow without any existing cultivation efforts.

Forestry Benefits to Agriculture

Unlike most ethanol feedstocks, which compete for available cropland with existing food and feed resources, growing additional forests specifically for synthetic fuel production would improve available agricultural lands in a variety of ways. Some of the trees being considered for biomass production have characteristics that make them beneficial to crops. For example, the paulownia and the tallow, as well as others, produce significant amounts of nectar to support beekeeping and assist in the pollination of other crops in the area. The hedge-row style planting typically used in tree plantations also makes an ideal habitat for raising free-range foul and small game. As noted previously, forests provide many vital services to the environment.

Trees in general neutralize the pH of the soils they reside in. In some applications today, trees are actually being used to remediate soils from toxic contamination. In particular, hybrid poplar plantations are being used today to clean areas contaminated by petroleum hydrocarbons, chlorinated solvents, pesticides, explosives and animal wastes. Tree plantations are also being studied for their abilities to assist in mining reclamation projects. Besides cleaning the soil, the root system of the trees loosens the surrounding soil to enhance the flows of moisture and oxygen through the soil. Moreover, when the trees are harvested, the root system is left behind to decay, adding nutrients to the soil to improve fertility.

It is not a coincidence that much of the existing cropland in the United States and elsewhere was originally forests – trees make the soil productive. So why not use tree plantations to help in improving the many fields that have gone fallow in the US from overuse and poor farming practices? Studies have shown that a 10-12 year cycle of tree growth can rehabilitate most soils including those with heavy contamination.

Tree plantations can also be integrated into many types of existing agricultural operations. Trees, especially those planted in high densities as is practice for energy purposes, can be vital in reducing farm run-off pollution in lakes and streams as well as limiting erosion in existing cropland. An estimated 140 million acres of grazing land in the US also happens to be forested as the animals feed on the grasses and other plants that naturally grow in areas where trees are prominent. In many cases, small tree plantations can be added to existing farms without using the existing cropland and because the harvesting is not time-specific, the equipment for harvesting can be co-op’d between numerous farms.

Forest Energy Objectives and Goals

The goal of energy independence should not be looked at as a short-term issue of economics – yes, the economics matter but if the “fix” isn’t sustainable, then we aren’t solving the problem at hand, we’re merely delaying it. Regardless of one’s stance on issues like Global Warming and Peak Oil, the one thing virtually all Americans can agree on is that the status quo for energy fuels cannot be maintained over the long term. When we will run out of oil is a matter of great scientific debate – THAT we will run out of conventional oil is generally accepted as fact. As shown, forests can play a vital role in achieving energy independence as well as achieving long-term sustainability in energy. But just how much area would need to be converted to energy tree plantations in order to effect this desired change?

Using existing conversion technology and tree breeds, 150 million acres in total would be sufficient to permanently alter the status quo. Depending on a variety of factors, this would be sufficient land to sustainably produce between 750 million and 1.05 billion tons of biomass per year, enough to displace about 50% of oil currently used for transportation fuels in the US. And many of the same systems that would be processing this biomass into fuels can also be used to process a variety of existing waste streams to further decrease our oil needs.

Now that may sound like a lot of land but one has to keep things in perspective. In a typical year, the farmers of the US will plant about 80 million acres of feeder corn and about 75 million acres of soybeans. Right now, there are over 40 million acres of cropland either already laying fallow or failing, much of which would be suitable for planting tree plantations. In Alaska, where food doesn’t grow well but trees grow just fine, there are tens of millions of acres suitable for tree plantations. Currently, there are roughly 788 million acres of land being grazed by livestock in the US, of which about 140 million acres are forested. And this doesn’t even include the over 500 million acres of existing forests.

Forests have played a unique role in the development of Man. When Man learned fire, he used materials from the forest. When Man needed shelter, he built it using materials from the forests. When Man needed protection and tools, he built them using materials from the forest. Much of what we know about all of the sciences was learned using materials from the forest. If we are serious about developing an independent, sustainable energy future, it might make sense to look where the answers to so many previous questions were found.