Long‐term variation in, and effects of fertiliser addition on, flower, fruit and seed production in the tree Sorbus aucuparia (Rosaceae)

In this paper, I present long‐term data on reproduction for the tree Sorbus aucuparia Variation in fruit‐set (6 yr) m 22 trees in one population is described and related to flower predation, climate and floral display size Fruit production is described for 7 yr m eight trees in each of four populations and related to climate An additional study, application of a mineral fertiliser, was conducted to test if nutrient availability affected flower, fruit and seed production The descriptive study showed that mean fruit‐set differed significantly between individuals and years The ranges of yearly mean proportion of initiated fruit/flower, mature fruit/initiated fruit and mature fruit/flower were large (12‐41%, 2‐72% and 0 3‐23%, respectively) Predation of flowers was low, 1% on average (range 0 3‐2%) Between‐year variations in fruit‐set were positively correlated (though not significant) with precipitation during the phase of initiation and maturation of fruits, respectively Fruit‐set was independent of floral display size when expressed as number of inflorescences per tree However, when floral display size was expressed as number of flowers per inflorescence, there was a tendency for large inflorescences to have a smaller proportion of initiated fruit/flower and mature fruit/flower than small inflorescences The number of fruits produced by the four populations studied varied significantly among years, populations and individuals Individual fruit production varied considerably between the worst and the best fruiting year (range = 10 1 ‐10 3 'x) Annual average fruit production m the populations was found to be in general positively correlated with precipitation the preceding year and negatively correlated with temperature, irradiance and fruit production the preceding year However, none of these correlations reached statistical significance In the fertilisation experiment, experimental trees produced significantly more flowers, fruits and seeds per tree, compared with control trees This increase was due to an increased number of inflorescences per tree and number of flowers per inflorescence In none of the years, irrespective of flowering, did experimental trees produce proportionally more fruits (i e larger fruit‐flower ratio) and more seeds per fruit than control trees Furthermore, experimental and control trees showed similar inter‐annual variation m flower and fruit production