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Forestry resources

Vegetable identification

Beam of light recognizes the chemical composition of species

Signey / WikicommonsA new identification method for tropical wood based on the spectroscopy technique, which measures the absorption of light energy by materials, is going to help in the recognition of forest species extracted illegally from the Amazon. Currently, the supervision of wood is based on a visual examination of the trunks that are being transported. “Mahogany, for example, can be confused with species like crabwood [Carapa guianensis],” says researcher Tereza Cristina Pastore, coordinator of the study that resulted in the new system at the Laboratory of Forest Products of the Brazilian Forestry Service, which is part of the Ministry of the Environment. By the new method, a beam of near-infrared light – a segment in the electromagnetic spectrum between 800 and 2,500 nanometers – coupled with a statistical model identifies precisely the vegetable species being analyzed in just a few seconds. “When the energy strikes the material the molecules vibrate,” explains Professor Jez Willian Braga, from the University of Brasília, who took part in the study. These are the molecules that supply the spectrum that is directly related to the chemical composition of a particular wood.

The response of the spectrometer is processed with the help of a database of spectra of certain forest species, which must be highly diversified and contain a large number of sample trees, from the sample of mahogany that grows in the State of Rondônia to that of Maranhão. “The more samples we have the easier it is to evaluate the spectra, because in the same species of tree there is a great variation in the chemical composition,” says Braga. When an unknown sample arrives, the researchers take the spectrum of the sample and analyze it using the statistical model constructed with the spectra database. The response is immediate. Previously, the chemical analysis of wood taken to the laboratory took at least a week. Near-infrared spectroscopy is already used to evaluate varieties of coffee that enter the blend of coffee bean roasters and also by the pharmaceutical industry, to find out the exact chemical composition of medication.

The model created by the researchers began with the choice of three tree species, which by the appearance and macroscopic characteristics of the wood can be mistaken for mahogany. These are crabwood, cedar and curupixá. Mahogany, sales of which are controlled worldwide, is one of the most valuable woods found in the Amazon Region. Its exploitation without criteria is a threat to the survival of this species, causing destruction of most of its genetic variability. “Mahogany populations may be damaged by the selective extraction process and by the destruction of its habitat,” says Tereza. In Brazil it can only be exploited with a forestry management plan to reduce impact, since it is a species considered to be in danger of extinction. “When a tree is standing it’s easier to identify it, based on an evaluation of its leaves, flowers and fruit,” says researcher, Vera Teresinha Coradin, from the Brazilian Forestry Service and a participant in the research. Analysis of cut wood, on the other hand, depends not only on the knowledge of whoever is making the identification but also on the state of the wood.

In the first phase of the work, the researchers ground the wood and then took it to the laboratory to prepare the samples that were to be analyzed by the spectrometer. The chemical responses associated with the statistical analysis of the data showed that it was possible to differentiate the species and this motivated a second stage in the research, an evaluation of samples of intact wood. Analysis was carried out for 111 samples, of which 66 were used to put together the information database of the species in the spectrometer, a process known as calibration. From the data obtained and from statistical analysis, models were created for classifying each species. The remaining samples served for validating the models. “We’re now entering a third phase, with analysis of the wood in a commercially available and portable device,” says Tereza.

Brazilian Forestry Service Microscopic images of mahogany (left) and crabwood: similaritiesBrazilian Forestry Service

Similar results
As the cost of this device is around – 20,000 and the researchers have not managed to buy it yet, the preliminary tests were carried out in France. The same samples tested in Brazil were taken there and produced similar, promising results. The portable device is going to facilitate the work of the inspector, who will be able to take the spectrum of the sample in the field and take it to the laboratory for analysis. “It’s also possible to set up a model, with adjoining laboratories and distribute it at certain ports, like Santarém, in Pará, and Paranaguá, in Paraná, from where a lot of wood leaves,” says Vera.

One of the spin-offs from the research is the use of the technology for differentiating the coal from native and from planted forests, which is bought by steel mills. “The coal used by steel mills has to come from a planted area or one authorized for exploitation,” says Tereza. However, this does not always happen. Laboratory studies managed to separate coal from wood that had been planted with that of native wood. An identification system must still be developed, similar to the one for wood. The problem is that the coal production process comprises different systems, as adopted by the coal producers. “The processes may have chemical differences that compromise identification,” says Braga.

Scientific articles
BRAGA, J.W.B. et al. The use of near infrared spectroscopy to identify solid wood specimens of Swietenia macrophylla. IAWA Journal. v. 32, n. 2, p. 285-96. 2011.
PASTORE, T.C.M. et al. Near infrared spectroscopy (NIRS) as a potential tool for monitoring trade of similar woods: discrimination of true mahogany, cedar, andiroba, and curupixá. Holzforschung. v. 65, p. 73-80. 2011.