Identification of the origin of Portuguese Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] provenances

Douglas-fir was introduced to Portugal in the 19(th) century and the first plantations were established at the beginning of the 20(th) century. Since then, it has been planted in the mountainous areas of the centre and north of Portugal. The Portuguese Forestry Service has generally accepted that the establishment of younger plantations has been carried out mainly using seed from existing plantations. Unfortunately, the native North American sources of seeds used for establishment of the older plantations are unknown. Isozyme analysis (seven loci) of megagametophyte tissue, from 10 Portuguese provenances sampled from across their introduced range (277 trees) and 17 native provenances, was used to investigate genetic variation: (i) among Portuguese Douglas-fir provenances; and (ii) between Portuguese and North American provenances of the 'coastal' variety, with the aim of identifying the putative source provenances for exotic Portuguese provenances. Among the Portuguese provenances, the expected heterozygosity (H-e) was 0.254, which was similar to previous investigations which sampled a wider range of the natural distribution. Therefore, these results reflect a considerable level of genetic diversity within Portuguese Douglas-fir provenances and may be evidence that the Portuguese material has come from more than one source. UPGMA clustering of Nei's genetic distances for Portuguese and native provenances showed the majority of Portuguese Douglas-fir provenances fell into a single, poorly resolved group together with provenances from across the native range of Douglas-fir. Whether all the Portuguese provenances in this group are the product of a single introduction from the native range and then separate establishment in different parts of Portugal or represent separate introductions cannot be resolved using the current data. Vila Flor, the only Portuguese stand of known native provenance (California), grouped as a distinct group with Soajo suggesting it may also have been derived from California but as a separate, earlier, introduction. The provenances from Lousa and Leomil form a distinct group, suggesting that the latter may have been derived from the former. This group is most similar to provenances originating from between Oregon and British Columbia and suggests that provenances from this region may have been introduced into Portugal. Overall these data suggest that at least three separate North American introductions of Douglas-fir seed may have been used to establish plantations in Portugal, two from California and one from Oregon, Washington or British Columbia. For future investigations of the origin of Portuguese Douglas-fir provenances in the native range, sampling of provenances in the native range must be much denser than presently undertaken and high resolution markers are likely to yield better results over the identities of the originating native provenances.