Human impact on the genetic diversity of Dutch field elm (Ulmus minor) populations in the Netherlands: implications for conservation

Background and aims – Field elms (Ulmus minor Mill.) can easily reproduce vegetatively by root suckers or sprouting. They also have a long history of propagation and planting in the Netherlands. Both natural vegetative reproduction and cultivation may significantly influence the genetic structure of U. minor populations and insight in these phenomena is of utmost importance for appropriate conservation management of this species. In this study we examined the presence and extent of clonality and patterns of genetic variability within and among field elm populations in the Netherlands.

Methods – We used microsatellites (SSRs) to describe the clonal diversity and structure and to calculate genetic diversity parameters in the Dutch U. minor populations. Additionally, we compared Dutch populations with two U. minor reference collections from Belgium and France.

Key results – We found high levels of clonality in the Dutch field elm populations. Out of the 159 Dutch trees analysed for clonal structure only 66 multilocus genotypes were identified. Clonal richness (R = 0.06–0.96) and diversity (D = 0.44–1.0) varied considerably among locations. Six genotypes were shared between locations indicating human-mediated translocations. We revealed a low to moderate genetic diversity in the populations (He = 0.483–0.628 and Ar = 2.4–2.9). At four locations some individuals were found that differed in assignment probabilities based on the STRUCTURE clustering analysis including parental species, suggesting that these might be hybrids or at least not pure U. minor specimens. This also indicates that morphological identification is difficult. When omitting these individuals genetic structure analyses still indicated the presence of two genetic clusters.

Conclusions – However artificial establishment has played a major role in the distribution of the species and its current genetic diversity in the Netherlands. These findings help facilitate Dutch gene conservation management programs for U. minor, in particular, the identification of high priority clones for ex situ conservation and efforts to restore remnant populations and hedgerows.