Processing forest residuas
Processing forest residuas

Typically when trees are harvested for lumber and pulp, the limbs and branches (commonly termed “forest residuals”) are left on the forest floor or collected in slash piles and burned. If these forest residuals were used instead to produce products such as biojet fuel, what effect would that have on our environment and how can we manage the resource to ensure environmental sustainability?

NARA (Northwest Advanced Renewables Alliance) is currently providing research to help answer this question. NARA is one of seven coordinated agricultural projects (CAPS) within the sustainable energy challenge area funded by the USDA National Institute of Food and Agriculture (NIFA) Agriculture and Food Research Initiative (AFRI). It is tasked with facilitating the development of a Pacific Northwest industry that uses forest residues to make chemical products such as biojet fuel.

This industry is anticipated to provide numerous benefits to society. As biofuels displace fossil fuels, U.S. energy independence is strengthened and net carbon emissions to the atmosphere are potentially reduced. A novel use for forest residuals can stimulate rural economic development and provide new ways to approach forest management that reduce fuel loads and improve forest health. And unlike corn-based ethanol that can create a financial stress on food markets, products such as bio-jet fuel, derived from forest residuals, do not compete with food production.

There are, of course, legitimate concerns to how this industry will affect forest ecosystems, water and air quality. The NARA project funds research to investigate these concerns and provide research-based analyses and conclusions so that regional stakeholders and society can make informed decisions. The purpose of this article is to describe the research within NARA that evaluates the potential impacts of forest residual harvest on forest ecosystems and the environment.

How are forest soils affected?

Forest vegetation and soil microbes need nutrients in the soil for healthy growth. When forest residuals decay, they can release stored nutrients back to the soil. NARA is funding research that develops effective models and methods to ensure that soil nutrient pools remain sustainable in working forests when limited forest residuals are removed.

Initially, NARA researchers measured the amount of carbon and nitrogen in soils at Douglas-fir plantation sites throughout the Pacific Northwest. Their measurements, when compared to the harvest history and soil type, provide a rough prediction tool to measure a site’s capacity to retain productive nutrient levels when residuals are removed.

Review of NARA publication on predicting nitrogen depletion risk here.

NARA research posters on soil carbon here

For a more detailed understanding of how removing forest residual can affect soil nutrient levels, NARA researchers have established long-term experiments at numerous sites in the Pacific Northwest. At one experimental site located on Weyerhaeuser land near Springfield Oregon, seeding growth and soil nutrient content will be measured over years from multiple plots subjected to various levels of forest residual harvest. Over time, these results will provide a clearer picture to how forest residual removal affect soil nutrient levels.

NARA research poster on NARA Long Term Soil Productivity Site here.

NARA research posters on soil carbon here and here

Test plot at the LTSP site in Springfield, OR: full residual removal
Test plot at the LTSP site in Springfield, OR: full residual removal
Test plot at LTSP site in Springfield, OR: no residual removal
Test plot at LTSP site in Springfield, OR: no residual removal








How is water quality and retention affected?

There is a need to investigate forest residual harvesting impacts on water movement, retention and quality at scales ranging from field scale to regional scale.

At the field scale level, water runoff, nutrient export, sediment erosion and microbial populations will be examined under various residual harvest options. These experiments are being conducted at the Springfield Oregon Long Term Productivity Site.

Based on this data, predictive models will be developed to determine water quality, quantity, and the effects on stream channels under various residual harvest scenarios at a regional scale. These models should provide a real impact to how residual harvest is managed so that water resources are protected.

NARA research poster on soil erosion here

What is the effect on wildlife?

A large body of experimental work is available that describes how wildlife interacts with downed woody material and snags. This existing information will be used to generate regional models designed to estimate the potential impact of forest residual removal on vertebrate abundance. In summer 2014, NARA researchers will produce a more detailed study that examines the relationship between white-crowned sparrow fledglings and forest residual slash piles. Casual observation suggests that fledglings are using slash as cover between the times that they leave the nest and gain the ability to fly. Data derived from this research combined with earlier studies will be used to model bird responses to forest biomass use.

NARA research poster on impacts to biodiversity here

How would this industry affect the atmosphere?

NARA is comparing the amount of greenhouse gas emissions, ozone depletion, and smog that would occur when a bio-jet fuel blend, using forest residuals as feedstock, is produced compared to jet fuel production from petroleum. The results from this assessment, called a comparative Life Cycle Assessment (LCA), are not only critical to determine environmental sustainability of the process, but also important to determine whether the products derived from forest residuals qualify as “renewable” under the Renewable Fuels Standard (RFS). Qualifying under these guidelines is critical to the economic success of the process.

The LCA traces the environmental impacts at all stages of development from forest residual extraction and transportation through to the finished product.

There is more work to be done to verify all the inputs and outputs of the process, but preliminary results show that producing jet fuel from forest residuals reduces global warming potential, measured in kilograms of CO2 emissions, by over 60% and ozone depletion by nearly 90% when compared to jet fuel production from petroleum. Contributing significantly to these results is that the practice of burning forest residuals in slash piles would be reduced, thus reducing the amount of smoke, ash and CO2 emitted to the air.

NARA research poster on air impacts here

NARA research posters on LCA here and here

NARA presentation on Life Cycle Assessment here

Private and public Lands

The supply chains being developed are influenced by the sustainable availability of forest residuals. Currently, the forest residuals considered are located on private, tribal and state lands. Due to access limitations and policy, the forest residuals from federal lands are not being considered in the analysis.

One area of public debate over federal forest management is forest fire mitigation. To provide science-based information for this debate, NARA researchers are working with regional forest managers to develop models and experiments that determine the impact of forest thinning on forest fire intensity. If these management prescriptions are implemented, a market for the residuals may help alleviate the cost of thinning programs.

NARA research poster on fire reduction treatments here.

Plenty of work to do

Generating biojet fuel and co-products from forest residuals places a new dynamic on forest practices and environmental impacts. The research funded by NARA will provide tools and analysis useful to determine these impacts. Now is the time to identify environmental concerns and opportunities associated with this emerging industry. Included in NARA’s outreach efforts, we will participate in the Public Interest Environmental Law Conference (PIEIC) in Eugene, Oregon this February. In addition, NARA is sponsoring a “Northwest Wood-Based Biofuels + Co-Products Conference” in Seattle April 28-30. This conference will feature speakers who will address the environmental issues surrounding woody biomass utilization for biofuels and value-added co-products. To engaged with NARA and receive information as research and analysis develops, connect at

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