Regions of provenance are a necessary tool: they are used as seed zones and they help determine which provenances are to be used in reforestation or afforestation to avoid the risk of using unsuitable ones. However, the delineation does not follow a standard method used in every country. A single delineation in regions is mostly used for all species concerned, while a more species-specific one would be more useful. This is mainly because of practical reasons and because of a lack of information on the population ecology of many species. This information can be obtained through provenance trails and/or from genetic research. The first is an effective but time consuming method, the second however is a more rapid source of information. Research like this can result in the delineation of new regions of provenance. We demonstrate this by a case study on Alnus glutinosa (L.) Gaertn in Flanders. This common species is often used in forestation projects. We gathered seed in 22 autochthonous populations. Leaves of 10 seedlings per population were used in an AFLP analysis, a marker technique that was not employed before on this species. Preliminary results show that the population differentiation was low, but not unusual for wind-pollinated tree species. Also, mainly one population was slightly different from the rest, which might be explained by hybridisation with Alnus incana. These findings however have to be further investigated. If future analysis and research corroborate these results, there will be a practical implication: Flanders will become the region of provenance for this species instead of the official delineation. This will be translated in a few guidelines for use in the field. Different channels will be used to communicate these findings to all parties involved.