The role of nutrients, productivity and climate in determining tree fruit production in European forests.

Fruit production (NPPf ), the amount of photosynthates allocated to reproduction (%GPPf ) and their controls for spatial and species-specific variability (e.g. nutrient availability, climate) have been poorly studied in forest ecosystems. We characterized fruit production and its temporal behaviour for several tree species and resolved the effects of gross primary production (GPP), climate and foliar nutrient concentrations. We used data for litterfall and foliar nutrient concentration from 126 European forests and related them to climatic data. GPP was estimated for each forest using a regression model. Mean NPPf ranged from c. 10 to 40 g C m-2  yr-1 and accounted for 0.5-3% of GPP. Forests with higher GPPs produced larger fruit crops. Foliar zinc (Zn) and phosphorus (P) concentrations were associated positively with NPPf , whereas foliar Zn and potassium (K) were negatively related to its temporal variability. Maximum NPPf and interannual variability of NPPf were higher in Fagaceae than in Pinaceae species. NPPf and %GPPf were similar amongst the studied species despite the different reproductive temporal behaviour of Fagaceae and Pinaceae species. We report that foliar concentrations of P and Zn are associated with %GPPf , NPPf and its temporal behaviour.