Electronic Noses and Forests

Diagnosing tree diseases is useful in forest industry. This cottonwood log has bacterial wetwood, which damages wood fibers. An e-nose can detect the condition, which otherwise would not show up until after the wood was kiln dried. Photo courtesy of Dan Wilson.

What if a machine could detect insects and diseases in living trees or help prevent log theft and illegal logging by tracking individual logs from the forest to the lumberyard? What about a machine that researchers could use to identify and understand the ecological roles of microorganisms, insects and other invertebrates that live in and on trees?

It may sound like the stuff of science fiction, but such machines do exist, and theyre called electronic noses, or e-noses. Dan Wilson, a U.S. Forest Service research plant pathologist with the Southern Research Station Center for Bottomland Hardwoods Research, recently published a 2013 review article on the uses of e-nose devices in agriculture and forestry in Sensors, a leading international journal on the science and technology of sensors and biosensors. Wilson recently received the 2013 Sensors Best Paper Award for his 2009 review article, “Applications and Advances in Electronic-Nose Technologies.”

E-noses mimic the mammal sense of smell, and while they are not as complex as the human olfactory system, they can provide real-time information about the chemical and physical nature and quality of plants, and┬áplant and animal products. E-noses “smell” with sensors, and recognize mixtures of gases rather than individual gases. Gas emissions at lumber mills and forest-product manufacturing facilities are often complex mixtures of gases, and e-noses are widely used to monitor, detect, and control hazardous waste emissions from these industries.

Plants make a wide range of chemical compounds, and many of these compounds boil at low temperatures, easily becoming airborne as gases. These compounds are called volatile organic compounds, and e-noses are especially useful for detecting them. Stressed plants, whether insect-infested or diseased, emit abnormal chemicals that e-noses can detect. This information can provide land managers and researchers important clues about whats happening below the bark. Wilson pioneered the use of e-noses in diagnosing tree diseases and identifying damaging insects like termites and microbial pests that cause vascular wilt, wetwood, and wood decay. Detecting wood decay early is especially important in urban forests, as falling trees or branches could injure people and damage property.

To find out the type of tree disease present in a living tree and which microbes are involved, an increment borer (the blue tool) is used to take a wood core sample to be placed in the e-nose instrument and analyzed. Photo courtesy of Dan Wilson.

E-noses can also be used to study the role of microbes, insects and other invertebrates in forests. These small creatures have a big influence on forests, causing trees to die and decompose, cycling nutrients and changing forest structure and ecosystem functions. “E-noses can help researchers determine the biological activities, interactions, and ecological roles of these creatures,” explains Wilson.

“E-noses are so precise that they can be used to track individual logs,” says Wilson. Forest Service managers can use e-nose devices to track high-value logs harvested on public lands from the forest to the lumber yard. This capability helps to prevent log theft. Similar methods potentially could be used on a broader scale to identify lumber milled from logs that had been taken illegally. Tracking bar codes on logs can be removed by thieves, but the aroma signature of individual logs can be used as a fingerprint to identify individual logs regardless of tree species or external markings.

E-noses are poised to become even more useful and accessible. “Engineers are beginning to design e-noses solely for use in specific industries,” says Wilson. “The needs and requirements of various industries are so vastly different and specific that more generalized (broad-based) e-nose instruments are often unusable due to their inflexibility. As e-noses become more customized for single applications, they require fewer sensors and will become more portable, affordable, and widely used in forestry, forest industries, and research.”

For more information, email Dan Wilson at dwilson02@fs.fed.us

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