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Experimental studies have been performed in order to alder trees (Alnus incana (L.) Moench.). Alder can grow rapidly owing to nitrogen fixation bacteria. The dead leaves of alder have a high nitrogen content. Nitrogen fixation was high even when the plants had moderate access to nitrogen in the form of ammonium nitrate. The nitrogen fixation activity was decreased by the treatment with occasional high amounts of nitrogen to the plants which were grown in the nitrogen of the air. Different clones of alnus exhibited a variety of growth, nitrogen fixation and biomass production. The length of cuttings could be used as an indicator of the activity of nitrogen fixation. The frequency of the plants which survived 2 to 3 years, was 72-100 %. The alnus has favourable qualifications for energy forestry, owing to : (1) Good nitrogen fixation (2) Good productivity in young plantation (3) Simple reproduction by cuttings and rooting (4) Possible genetical improvement (5) Not being consumed by the deers.