Use of the N2-fixing grey alder,Alnus incana(L.) Moench, as a short-rotation crop for energy production is currently being explored. To evaluate the need for inoculation of alders, the distribution of infective propagules ofFrankiain the soil at potential sites for alder plantations was examined. Uninoculated grey alder seedlings were grown in three types of soil. Frequent nodulation was found in a meadow soil which had been free from actinorhizal plants for nearly 60 years, but the alder seedlings failed to nodulate in peat soil from two different bog sites. One of these bogs had been exploited for peat and the surface layer of the peat had been removed, so that the soil samples were taken from deep layers of the peat. At the other site, an area of cultivated peat, there were no infective propagules ofFrankiain plots without alders; the infectiveFrankiawas present in plots only where it had been introduced by inoculated alders. There was no detectable air-borne dispersal ofFrankia. Instead, water movement might account for the dispersal ofFrankiain peat. Although the apparent absence ofFrankiain these peat soils necessitates inoculation of alder seedlings before planting out, this makes it possible to introduce and maintainFrankiastrains with selected beneficial characteristics, since there is no competition from an indigenousFrankiaflora.
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