Variation in male and female sex allocation and how environmental factors control this variation among individuals are important life history issues that are not often studied in long-lived perennial plant species. Here we report on 40 trees of three California oak species in which we measured aboveground annual net primary productivity (ANPP), female, and male allocation over a five year period.

Results/Conclusions

ANPP varied from 400 to 1600 g biomass m-2 canopy area, and differed significantly among the three species. We found that ANPP increased with higher water availability and higher soil nitrogen for each of the three species. Reproductive allocation varied between 5% and 40% of ANPP. Long-term acorn productivity (measured from 1980 to 2007 of each individual tree) increased linearly with ANPP. Not surprisingly, both total absolute reproductive allocation and absolute female allocation increased linearly in individuals that had higher average long term acorn productivity. However, absolute male allocation was not related to acorn productivity.  Higher absolute female allocation in conjunction with constant absolute male allocation in trees with higher acorn productivity leads to a pattern of decreasing relative male allocation in trees that have higher acorn production and higher relative female allocation. Variation among male and female sex allocation was high, with individuals at sites with poor productivity allocating up to 80% of total reproductive biomass in male catkins and individuals at the most fertile sites with the highest ANPP allocating up to 95% in female reproduction. These reproductive patterns were significantly different among species but showed the same general patterns. We conclude that there is fixed male sex allocation in these species of California oaks independent of site fertility. In contrast, increased site fertility corresponds with higher female sex allocation, leading to increased total reproductive allocation. Thus, female, but not male sex allocation is environmentally controlled in these three oak species.