Extractives are present in much larger amounts in knotwood than in heartwood in the 12 tested hardwood and softwood species. The chemical identity of the extractives varies largely among species, lignans being only present in softwood species. Extractives from knotwood may constitute an important source of new chemicals and remain still poorly known. The content of extractives (and particularly lignans) in knots was compared to that of heartwood in a number of different European softwood and hardwood species.

Twelve species characteristic of European forests were sampled. Extractions were carried out with four solvents of increasing polarity (dichloromethane, acetone, toluene/ethanol and water). Gas chromatography-mass spectrometry (GC-MS) was used for the identification of the compounds present in acetone extracts which are expected to contain lignans.

In all tested species, knotwood presented larger contents of extractives than heartwood. The main compounds were lignans, stilbenes and flavonoids, lignans being present only in softwood species. With the exception of oak, knotwood in softwood species contain larger amounts of extractives than that in hardwood species.

The chemical nature of extractives present in knotwood varies with species. Their amount is generally much higher in softwood than heartwood species.

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