Reproductive strategy of a temperate canopy tree Tilia cordata Mill. (Malvaceae) is related to temperature during flowering and density of recent recruits

Facultative clonality is extremely common in plants, but the relative emphasis on sexual versus asexual reproduction varies both between and within species, which in turn may influence individual fitness and population persistence. Tilia cordata is a temperate, entomophilous canopy tree that is partially clonal. Favourably warm climatic conditions have been linked with successful sexual reproduction in the species with clonality being suggested as the reason for population persistence in colder periods. Despite this the extent, character and structure of asexual reproduction in the species have never been described, nor has its relationship with climate. Fine-scale spatial genetic structure was assessed in 23 stands across a latitudinal gradient. The proportion of individuals that are of clonal origin has a wide range with a mean of ~43%. Genetic diversity is high, with even mostly clonal stand possessing several distinct genotypes. A beta regression model shows that historic summer temperatures and density of recent recruits are predictors of the proportion of clonal recruitment. Clonal reproduction is less important in stands that experience higher temperatures during flowering while stands with more saplings have more clones. Additional factors likely affect the balance between the two reproductive modes. The climatic relationship suggests a trend towards a higher proportion of recruitment from seed in a warming climate, although factors such as herbivory may prevent this.