Clonal structure and recruitment in British wild cherry (Prunus avium L.)

The extent of clonal reproduction may significantly influence the genetic structure and reproductive ability of wild cherry (Prunus avium L.) populations. In this study we used simple sequence repeat (SSR) variation to examine the relative frequency and distribution of vegetatively derived wild cherry in two ancient woodlands subject to contrasting management regimes. The probability of identical genotypes arising through sexual reproduction was determined to be negligible, both statistically and through screening a large population of known full-siblings. Only 246 genotypes were identified in the 551 trees examined from the natural populations. Thus, asexual recruitment accounted for a significant proportion of trees. Forty-five genets with multiple clonal trees (clonal groups) were identified. Clonal trees accounted for approximately 48% and 65% of all trees in the managed and unmanaged sites, respectively. Wild cherry trees were distributed in an aggregated manner, but to a stronger degree in the unmanaged woodland which was characterised by a disrupted canopy layer created by storm damage. However, clonal groups were generally non-exclusive in their distribution and displayed a ‘guerrilla’ strategy where further single and multi-ramet genotypes commonly shared the territory of the dominant clone. The clonal groups at the managed site were more exclusive than those in the unmanaged site. Evidence of somatic mutation occurring within clonal groups (i.e. where neighbouring trees matched at all except one locus and the disparity between groups was restricted to a single SSR repeat unit) was also observed, adding further complexity to the clonal structure of wild cherry. Natural disturbance and woodland management appear to influence clonal structure at this study site. Clonal genets in the unmanaged site contained significantly higher numbers of significantly smaller ramets and, on average, covered less than half the area of clonal groups at the managed site. Recruitment, both asexual and sexual, was also markedly higher at the unmanaged site and disproportionately high in years following major winter storms and attendant disturbance of the canopy. Whilst high levels of clonality were observed in both sites it is likely that self-incompatibility and the ‘guerrilla’ strategy of clonal growth adopted by wild cherry enable relatively high levels of genetic diversity to be maintained. Our study suggests that a policy of non-management, especially following winter storms, may help maintain genetic diversity through increased levels of both sexual and asexual recruitment in wild cherry.