Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on I I ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2-0.7%) was low compared to the ash content in the bark tissues (1.9-6.4%) and the foliage (2.4-7.7%). The woods' content of ash-forming elements was consequently low; the highest contents were of Ca (410-1340 ppm) and K (200-1310), followed by Mg (70-290), Mn (15-240) and P (0-350). Present in the wood was also Si (50-190), S (50-200) and Cl (30-110). The bark tissues showed much higher element contents; Ca (4800-19,100ppm) and K (1600-6400) were the dominating elements, followed by Mg (210-2400), P (210-1200), Mn (110-1100) and S (310-750), but the Cl contents (40-330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100-25,000ppm), P (1600-5300) and S (1100-2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820-1360) and its needles the highest Si content (5000-11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden. (c) 2005 Elsevier Ltd. All rights reserved.