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Three elm species are native to Poland: wych elm (Scots elm) (Ulmus glabra Huds.), field elm (U. minor Mill.), and European white elm (fluttering elm) (U. laevis Pall.). The epidemic of Dutch elm disease (DED) has led to a decrease in the popularity of elm cultivation. An analysis of forestry data was the first step in the assessment of elm resources. The area of forest stands where elms are dominant has more than doubled since 1978. Lowland alluvial forests rank first in regards to the number of elm localities per unit area of a given forest site type. While this site type is clearly preferred by elms, the majority of elm trees are actually scattered among sites of oak-hornbeam or closely related forests (of the alliance Carpinion betuli). Field research revealed a clear dominance of U. laevis, a species which in the past was predominantly located out of woodland and rarely cultivated. Data analysis indicated that all trees greater than 70 cm in diameter belonged to this species. Data from plots surveyed directly also suggest that the three elm species have slightly different habitat preferences. U. laevis prefers riparian habitats, although the major part of its resources is now on potential sites of oak-hornbeam or closely related forests. U. minor even more often than U. laevis occurs at less humid sites (mostly potential sites of oak-hornbeam or closely related forests), while U. glabra prefers moist slopes. In general, it appears that the impact of DED in the last 20–30 years has been smaller than in the preceding period, however, the disappearance of the disease has not been established. Undoubtedly, U. laevis is the elm species that is least impacted by DED
Wych elm (Ulmus glabra Huds.) is a rare scattered forest tree species in Poland. First studies on genetic diversity of the species in its natural range in Poland give a good basis for the management and conservation of its genetic resources. In the present study, we determined the level of genetic variation and genetic differentiation of seventeen natural Wych elm populations in Poland using nine nuclear microsatellite loci. The number of analyzed individuals was 601. The level of genetic diversity of Polish populations of Wych elm corresponded with the results of the previous studies on this species in Europe. The populations show quite low level of genetic diversity of the species on the population level and quite high diversity on the interpopulation level. A total of 119 alleles was found, with average number per locus (A) equal 6.0 and allelic richness at medium high level (AR10=4.7). Observed (Ho) and expected (He) heterozygosity reached 0.583 and 0.602 respectively. The genetic differentiation between Polish populations of Wych elm occurred at a low level (Fst=0.089). Inbreeding depression may occur in the next generations (Fis=0.031). Genetic diversity between Wych elm populations in Poland may be the result of unfavorable random processes related to the reduction of population size resulting from elm disease. To better understand the processes related to the genetic diversity of Wych elm populations, research on field elm variation should be undertaken. Such studies may give an answer to the potential influence of introgression between these species on the genetic structure of the Wych elm. Both in situ as well as ex situ conservation measures are highly recommended to preserve genetic resources of this valuable noble hardwood species in Polish landscape.
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